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Looking under the street lamp again

Freeman Dyson recounts an anecdote in his memoirs from the second world war, during which he worked as an analyst for RAF Bomber Command. Part of his job was to work out what parts of RAF heavy bombers were critically vulnerable to damage and needed extra armour. To do this, he and his colleagues examined aircraft that had returned to base after being badly damaged. They'd map out the areas that were most frequently holed ... and apply armour everywhere else. (The point being that, for a given chunk of airframe, if no bombers made it home with damage to that area, then damage to that area was very probably fatal.)

To identify the most lethal risks you must identify the situations where nobody has survived to deliver a warning ...

Here's another similar puzzle: myocardial infarctions (heart attacks) in Scotland. The last figures I saw suggested that a first heart attack is fatal to about 48% of men who experience one. (Subsequent heart attacks are less likely to kill, although they're still serious.) However, among men who presented at a hospital within three hours of onset of symptoms the survival rate for a first heart attack was around 90%. Which leaves us with a dilemma. Are first heart attacks in Scotland instantly fatal to nearly half their victims? Or could it be that around half the patients mistake their symptoms for bad indigestion, or an asthma attack, or just don't want to complain about the chest pains?

My money is on the latter — that most of the lethality of first heart attacks is down to the victims not being familiar with the symptoms and understanding their urgency — but of course we can't be sure: the people who could tell us are all dead. (We could run a health education program targeting the most vulnerable demographic, then see what happens to the survival rate, but that doesn't tell us about the people who have already been affected, or the bombers that never came back.)

It seems to me that space colonization and especially interstellar colonization missions using a generation ship may pose an extreme version of this paradox, which is a thinly veiled variant on the old anecdote about the scientist who has dropped his front door keys at night. (A neighbour finds him on hands and knees, hunting the sidewalk, and joins in. But there' s no sign of any keys. "Well, do you know where you dropped them?" asks the neighbour. "Oh, over there!" The scientist waves at the darkness down the street, between lamps. "Well, why are you searching here then?" "Because I can't see in the dark ...")

In previous discussions, I've looked at the minimum complexity of a biosphere necessary to support human life indefinitely (hint: blue-green algae and tilapia and soy is not sufficient). And asked what minimum population size is needed to support the skills and knowledge needed to maintain a modern technological civilization — as a proxy for the skills and knowledge needed to maintain a generation ship or space colony. I'm not even going to start asking what tools and techniques we'd need to colonize a terrestrial planet lacking an Earthlike biosphere — let's just say that it's obviously non-trivial and move swiftly on.

It seems to me that we don't currently know the extent of our own ignorance of the obstacles to interstellar flight. But by the same token there are some things we could do to start probing the blind spots. Assuming we ever get cheap-enough access to Earth orbit that asking these questions makes any kind of sense, then it follows that we should try and probe the extent of our ignorance before we get too far from home to evacuate.

So, proposal: before actually sending out a generation starship, a necessary first step is to assemble the habitat section, populate and provision it, and boost it out to the Earth-Sun L2 point (a stable solar orbit in Earth's shadow, about 1.5 million Km further out from the sun). L2 is a good proxy for interstellar space — it's in perpetual shadow and very cold — and if we can run a self-contained and unreprovisioned habitat there for a century, then we can probably strap a propulsion system to it and run it for a century-long interstellar cruise. On the other hand, it's close enough to home that if the biosphere crashes due to some obscure micronutrient cycle going nuts, it (and its inhabitants) can be brought back to Earth orbit.

In the absence of such an experiment, sending out a generation ship would be wasteful: not only would we be sending it out in ignorance of all the risk factors, but if it failed it would not return any useful information about the cause of failure. Just as the pilots of a stricken airliner seldom know exactly what's gone wrong (much less take the time to explain it to the flight voice recorder), we can't rely on the crew of a generation ship to diagnose a problem that they've allowed to arise. If they knew what caused the crisis, then almost by definition it wouldn't have arisen in the first place. They're having a first heart attack and they don't know what the symptoms are.

Those who're sending out the starships need to know where to bulletproof the design. And I doubt that starships will ever be cheap enough (or go missing frequently enough) to apply Freeman Dyson's world war two statistical methods successfully.

580 Comments

1:

Reminds me of JG Ballard's early story "13 For Centaurus", which involved a similar dry-run, but one focusing on the psychological problems.

A real starship could tell us about its failure if it were sending back continuous data -- more than telemetry, it'd have to include video of the interior and such. The bandwidth needed would probably be infeasible over such a distance, but if you ignore that it could be an interesting story hook -- watching the grand experiment go down in flames, with all lives lost, from a light-year away and many years after the fact, with nothing one can do about it. It'd be like a very macabre reality show.

2:

This seems like the (totally valid) interstellar equivalent of the "Hudson Bay start," whereby trappers in Canada would make camp for one night just outside of civilization, and ensure that they hadn't forgotten anything or brought anything bogus and unnecessary.

3:

Why would the bandwidth be infeasible? Unless the disaster strikes instantly, the crew ought to have a few hours (or weeks or months) to summarize their thoughts on the problem and send them out via tiny textual emails.

And on the other hand, even our ancient small space probes still manage to send back pictures and other telemetry; hopefully a few centuries advanced asteroid-sized generation ship could manage to broadcast back a few MB/sec. A few gigs a day can go pretty far.

4:

I'm in essential agreement with you, but I think that just one space colony is an infeasible approach. You need *lots* of them. And people who like to live in them. So they need to be economically profitable. (Which means they won't be truly isolated, but at least you can carefully track imports and exports.)

Eventually you build some to mine the Oort clouds. Pretty thin resources there, so they need a built-in drive and they have almost total isolation. Then a political or religious disagreement will send colonies dispersing.

The colony isn't likely to leave for the sake of exploring. You're talking about people's HOMES. When families leave to pioneer, it's always in search of "greener grass". It's never just to explore. But if they already make their living mining asteroids and cometary heads, then it's a lot easier to move on to somewhere else. And these would be groups that had already reduced their imports and exports to nearly nothing.

P.S.: This would clearly require controlled fusion, or something better, to be possible.

P.P.S.: I'm not sure what the density of condensed matter is in interstellar space, but I'm assuming that it falls off in a steady manner with the distance from a star. The last time I checked there wasn't any existing way to measure such things as "loose planetesimals", or even "loose planets", but to me it seems intuitively obvious that the law of "the bigger, the fewer, the smaller, the more numerous" should be presumed to be continuous from SuperGiant stars to dust motes. It might not be, but presuming that something isn't there just because you have no way to measure it is...unreasonable.

5:

Your anecdote about Dyson reminds me of another I heard about Henry Ford: how when he was seeking to lower the costs of the Model T in order to make it more affordable to the masses, he had his engineers examine each report from the mechanics and search for the pieces that never broke. He then ordered them to cheapen the quality of those very pieces, stating that they were being produced to too high a standard. Ha!

6:

The assumption is that the risks can be mitigated and that these were the dominant risks.

If it turned out the dominant risks were purely random, e.g. hitting a very small rock at relativistic speed, then the approach wouldn't work.

Following the same theme, if the risks were due to the environment associated with relativistic speed (even your slow generation ship speed), then a solar space colony will not be tested appropriately.

Dyson's approach reminded me of a small item I once read about there being "null DNA sequences", i.e. short sequences of nucleotides that never seem to occur in the data sets. It was speculated that these could be lethal. These sequences were short enough that they couldn't be interpreted as simply statistically unlikely.

7:

For an interstellar ship, bandwidth isn't the problem, it's latency. (cf Our Host's quantum workaround in the Eschaton books)

8:

Not just latency, although if you've sent out Ship #3 before you get the info on what killed Ships #1 and #2 that's a problem The other thing is that sensor/telemetry tech is still no substitute for hands-on postmortem examination. If your test colony in the Oort Cloud goes pear-shaped, you've got a much better chance of getting another ship out there to take a look at it than if the thing were halfway to Tau Ceti.

9:

This L2 habitat is a great setting for a novel.
Any specific reason why Accelerando lobsters were at L5?

10:

If the crew manages to work out what the problem is, then it's likely not fatal, so any report you do get will likely be inconclusive.

11:
I'm not sure what the density of condensed matter is in interstellar space, but I'm assuming that it falls off in a steady manner with the distance from a star.

IIRC the Voyager data from out near the Heliopause contradicts this assumption. While the standard model for frequency of a given size object in interstellar space is a power law, this hasn't been checked for substellar masses as far as I know, and I would not be surprised to find that for very small objects (e.g., pebble-size and down) the frequency varies quite a bit over long distances, depending on gas and dust currents, solar winds, differences in the temperature of the interstellar medium, etc. Given our lack of knowledge it would be prudent to send probes out in the directions we intend to send generation ships later; luckily the probes don't need to be complicated, they need only be mockups that approximate the collision cross-section and velocity of the ships to come later.

We might find after testing long-duration biosphere maintenance that it would be simpler to colonize the Kuiper Belt, or even the Oort Cloud than to send out generation ships to the nearer stars. We might even do both. I suspect that a lot more colonists could be sent out to the edges of our own solar system than to others. This of course would require cheap fusion for a power source as there's not enough sunlight out there to make solar power practical.

12:

This of course would require cheap fusion for a power source as there's not enough sunlight out there to make solar power practical

AhaHAHAHA(cough) ...

"Cheap fusion" is of course fifty years away. (Just like it has been for the past fifty years.)

I'm not saying it's impossible, but I think a reality check is in order at this point: it's safe to say that achieving exothermic fusion is non-trivial, and doing so with a viable fuel cycle and without it weighing a lot is going to be difficult.

13:

Charlie, I'm sure you're familiar with this:

https://secure.wikimedia.org/wikipedia/en/wiki/Non-Stop

What you're talking about is quite a bit more intentional and I'm sure any story you'd hang on it would be wildly different.

14:

So, being in near perpetual shadow, are we talking RTGs for power, if we assume that practical fusion never arrives?

15:

If practical fusion never arrives, then interstellar colonization by unmodified mark one humans is probably off the agenda, permanently. (You can travel fast, which takes a buttload of energy, or you can travel slow, which takes less ... except you've got to carry an energy source in order to stay warm and grow crops. Oops. I'm not sure any of the literature on generation ships has ever really looked into the energy budget such a ship would need, summed over the long term, and examined how much fuel it takes to keep such a biosphere running.)

16:

"Why would the bandwidth be infeasible?"

Because you don't know what information would be relevant, so you have to measure everything.

"Everything" of course actually meaning "everything you thought of specifying beforehand" which is congruent with the original problem.

17:

Irksome. I suppose tethering the habitat to the sun with a mirror and a laser Star Wisp-style would probably be too inefficient. But like you said, there doesn't seem to be much data on total energy throughput.

And even if the smallest naturally occurring star is, say, 0.08 solar masses, that's still really big and awkward.

18:

Apollo 13 -- the first inkling of the problem was a bus undervolt i.e. they had lost one of their main power supplies. What nearly killed the crew was CO2 buildup and it took a miracle of improvisation to keep them alive long enough for them to make it home. All the time they were relaying information about their situation to Houston. If they hadn't been able to duct-tape a CO2 scrubber together from parts in the Lunar Lander they could well have died knowing exactly what was killing them and having told Houston all about it.

19:

On a smaller scale, one (of many) ways in which the ISS is a bit of a waste is that it could at least have been a prototype for a Mars or general Solar System ship but is specifically designed for relatively short duration crew missions and continuous resupply. One (of many) advantages of getting rid of the Shuttle is that it has at least put some pressure on them to reduce the amount of supplies needed - in particular, they've got the water recycling sorted out to some extent in the absence of the Shuttle's fuel-cell water transfers.

20:

Note, however, that they didn't design the duct-taped CO2 scrubber themselves; that happened down on Earth, where Mission Control grabbed the backup astronaut team, a bunch of engineers who'd worked on the LEM and CM, and actual units of every item available to the crew and said "you have six hours to make an airtight fit between square cartridge A and round socket B or your mates die".

Once they'd brainstormed a viable design CAPCOM then talked the Apollo 13 crew through assembling it.

(How this might work when "Apollo 13" is a generation ship two centuries and a light year or so out-bound from home, "CAPCOM" is whatever civilization is still bothering to listen to the antique receivers, and the minimum reply time is two years or more is left as an exercise for the imagination, but my guess is "badly".)

21:

The last figures I saw suggested that a first heart attack is fatal to about 48% of men who experience one. However, among men who presented at a hospital within three hours of onset of symptoms the survival rate for a first heart attack was around 90%.

This depends on what your time related criteria for survival and fatality are. Perhaps 90% of those who reach hospital within three hours (or, more accurately, are thrombolysed ASAP) survive to make it out of hospital, but perhaps only 48% are alive at five years because of a lack of secondary prevention.

Sorry, but your analogy has awoke my Inner Ben Goldacre.

22:

If the Polywell fusor scales at r^7 as Bussard thought and it gets a tithe of the funding that is being wasted on ITER (~$25B), it might only be 5 years for the first reactor with net power output, 15 to making it commercial and perhaps not much more to aneutronic H-B11 demonstration at net power output.

Since most of the weight is in the vacuum containment and larger reactors are less dense, space reactors could be reasonably light for their output, particularly with aneutronic direct-conversion (fast charged particles-> electricity) and a proportionally smaller heat engine.

Waste heat is still a big problem, though, especially in space. Even most hard SF doesn't really deal with this fundamental problem of all energy sources.

23:

However, the message "we're dying of CO2 poisoning" may not have been all that helpfull, what would really have been usefull would be "the saftey valve on tank b was faulty, leading to an explosion". It's not clear whether the proximate cause or non-proximate cause is wanted.

24:

I have this dreadful feeling we're going need gravity control to make any of this work.

That might just be seasonal affective disorder talking, though.

25:

This is why we need to build on Mars, build on asteroids, and yeah, L2 is a good idea. Not to mention undersea habitats and Antarctica and the Gobi Desert - we're not even close to understanding real life support without a planet and most of the goods parts of the planet.

26:

The self sufficient space colony isn't the first step, the first step is set up a totally self sufficient self contained habitat on Earth. It's cheaper to set up and if things go really wrong there is a breathable atmosphere just outside. Get that working first then try it in microgravity.

27:

how come noones mentioned the dyson sphere? i remember reading somewhere where they said if extraterrestrials were here they would come by nanotechnology,
first we have to figure out where where is we might be in the middle of a unvirsal nexus for all we know, we haven't progressed to the technological point yet where well see that if you can see billions of years into the past why can't we se billions of years into the future, i think humans will succeed to explore and setup outposts in interstellar place but myths is where it really is at, we wouldn't be here if it wasn't for myths.

28:

I think mister Stross talked about putting a spaceship in L3 orbit in one of his previous blogs. And someone mentioned, that no-one would want to stay in a ship that's not going anywhere. I though about it and got a solution. You tell those people that it's a spacestation and it's doing a secret work on faster than light drive. You could put people in there for 15 years, before they figure it out. After that you could just put engine section on it and off they go.

This gave me an idea for a short story. After couple of generations, something goes wrong in the engine section. Those that are sent there do not come back. After two more generations they sent another young man in, like they have done in every 10 years or so, to do something... Like in an ritual, without remembering the real reason.

About energy on generation ship, it's not necessarily the energy source that is the limiting factor, it could be the amount of heat that radiates out of the ship.

29:

Thorium fluoride salt reactors might be able to provide the power needed for a generation ship, too. Here's a back-of-the-envelope calculation:

Since Thorium can be burned nearly completely, the net usable electrical energy equivalent after losses is over 30 TJ/kg. Enthusiast sites quote $2/W reactor costs (vs. $4 for conventional PWR). One can adjust that by whatever fuge factors one chooses, but assuming a conservative $4/W and $80/kg that's:

20W/kg, (= 50M kg/GW) plus a negligible 1 tonne fuel/GW-year.

(The dollars divide out and are just for estimating mass - the actual costs would be much greater.)

Assuming on the order of 100,000 people at 100 tonnes habitat each, thus 10B kg total habitat mass, a power plant on the order of 10GW or a bit more (500M kg, 5% of total mass) with output up to 1000 years should be feasible (with spare raw materials on the order of 1M kg/yr and remanufacturing of components every 30-50 years).

Assuming 8 GW to propulsion and perfect conversion of electricity to habitat kinetic energy, that gives a theoretical acceleration limit of ~1.25 m/s^2, which is over 1.5 orders of magnitude more than needed to get to 0.1c in 25 years, indicating that a generation ship could potentially be able to be engineered with this density of power source.

30:

I'd suggest that parking a generation ship at L2 only addresses the easy part of the problem. Unless they are going out for a never ending drive, they are going to need to land/terraform/survive/thrive on an alien world. With only what they can take with them.

As such, I'd suggest a Mars colony, and a Venus one, would be more practically useful in gaining applicable knowledge.

Mind, I still think mine host's 'lets all live in a software simulation' is more practical - although I've never been sure why you wouldn't just store the data 'turned off'?

31:

I'm with Vivtek on this one. We've got to be able to settle everything out to Sedna before interstellar generation ships are worth the trouble. And yes, sustainable, technological civilization on Earth is a *really, really good* first step.

This is actually points to the biggest problem with all generation ship stories: the culture that would support interstellar colonization on a slow ship won't look much like ours, any more than ours looks like, say, the Victorian era. Making the story both accessible and sympathetic is a huge issue, because the author has to both figure out what the technology will look like, then design the culture to fit it. As a starting exercise, try making Danger Mouse's Grey Album understandable to the 1880s readers of penny dreadfuls.

32:

Just because it's "the easy part" does not mean running the experiment is invalid or pointless, surely?

33:

take a look at sea turtles, and see how they fare, out in the deep, thats what there looking at and then some

34:

Can I just add my vote to: "sensor/telemetry tech is still no substitute for hands-on postmortem examination" coz I'm one of the people who has done that postmortem.

When several hundred million dollars worth of rocket went bang and they picked the mangled bits of metal out of the ocean, they sent it to our lab. The telemetry just suggested a major, sudden thrust diversion which, frankly, could have been bloody anything. Once we got the six-inch square remains into the lab, the cause was obvious - creep-fatigue in a engine part that was getting far hotter than the models said it would. They thought the models were good enough, but the only way to find out is to fly the bugger.

Yes, you could have had more sensors and more telemetry (discounting the immense vibration & temperature ranges that this part was under), but frankly, if you don't know what you're looking for, then you don't know where to look. If you know the failure mode, then you can engineer to stop it failing. It's the new failure modes you don't know that kill you.

35:

Before even thinking of trying out an habitat at L2 or on Mars or on the Moon I would like very much to see some long term experiments in Earth orbit in three different wheels spun for Lunar gravity, Mars gravity, and Earth gravity. We don't know if humans can survive Moon gravity for long. Same thing with Mars gravity. We don't even know if giving a spin to an habitat wheel is healthy for simulating 1g. And how about fish, goats, poultry? Can they thrive in three spinning wheels?

We're not even sure just how much radiation shielding is necessary over the years, for a space faring society which actually wants to have healthy children out there. You can get all those answers in low Earth orbit. You don't even have to reach high orbit, much less L2.

36:

I'm not sure about the gravity thing, all the studies about the negative effects of gravity deprivation are about how those effects manifest when people return to 1G. If you never plan to return to Earth low gravity might not be an issue even now.

It would be interesting to conduct experiments to see if children can be born and develop normal intelligence in freefall. Maybe those can be done with chimps(to be able to test intelligence).

One problem that might be interesting is children growing into giants under freefall conditions, to the extent that they might not fit into their parents habs. Perhaps some kind artificially induced dwarfism might be in order.

37:

Development in free fall might be quite interesting with values unpleasant to the afflicted of interesting; even if there is not that much of a direcr effect on intelligence, there might be subtle differences in some neurocognitive domains, e.g. the development of our spatial orientation with some nonstandard input from the vestibular organ should be interesting.

Another interesting area opens with the circulatory system, see orthostatic tolerance, especially if some of the signal molecules involved play part in the development of e.g. the heart.

Problem is, as you learn early when you're into genetic knock-outs, there are multiple back-up systems for many developmental pathways. But then, if all of these back-ups are prone to gravity, we are into problems; and diminuished (why not enhanced? better blood supply with lower blood pressure...) intelligence is of limited interest, when our jury-rigged quadruped cardiovascular system meets unexpected problems not seen in real quadrupeds like mice, and people die with 30 thanks to heart valve problems...

38:

Ignore that kinetic energy/acceleration calculation at the end, it's off by a few orders of magnitude. Power-wise, it's plausible, (10 GJ/s = 0.5(10^10kg)*((delta.v)/s)^2, delta.v/s=1.26 m/s^2 but taking the overall KE of the ship at 0.1c it's wrong by nearly 6 orders of magnitude. (4.5E24J vs. 6.3E18J) The fuel alone at 3E13J/kg would mass 15 times the assumed weight of the whole habitat. It looks like fission wouldn't work for velocities greater than about 0.0001c and fusion wouldn't be much better.

40:

[1] Thorium-uranium nuclear fission generation for internal power systems and fission pulse drive -- as in Dyson's Project Orion -- are the obvious candidates for power systems.

Dyson's preliminary calculations on the feasibility of fission pulse drive for reaching Alpha Centauri --

http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

"At 0.1c, Orion thermonuclear starships would require a flight time of at least 44 years to reach Alpha Centauri, not counting time needed to reach that speed (about 36 days at constant acceleration of 1g or 9.8 m/s2). At 0.1c, an Orion starship would require 100 years to travel 10 light years."


[2] Charlie writes: 'If practical fusion never arrives, then interstellar colonization by unmodified mark one humans is probably off the agenda.'

Orion-style speeds put interstellar flight notionally within unmodified lifespans. But free-range humans are probably still not fit for purpose. Low-gee conditions mean deconditioned cardiovascular and vestibular systems, and also repositioned internal organs, all requiring somatic and germline engineering to stabilize metabolisms.

[3] Given that gene modding is a necessary part of your interstellar trip, then, why not just go the whole hog and strap a fission pulse drive to a Dyson tree?

http://en.wikipedia.org/wiki/Dyson_tree

This approach might obviate some of those problems that Charlie mentions about powering your biosphere. Thorium-uranium fusion piles could do the rest.


41:
You can travel fast, which takes a buttload of energy, or you can travel slow, which takes less

Traveling fast (comparatively high acceleration == high thrust) takes a buttload2 of power, which bumps the mass of the power source up at the same exponent. Frankly, I don't think a generation ship is going to be practical at less than 0.01 c; it'll take so long that 2 rounds of long-term testing followed by one real flight (which is the minimum that sounds reasonable to me, figuring something's going to go wrong on the first test) would take 2 to 3,000 years for a trip to Tau Ceti. I can't see any human civilization putting that kind of long-term effort into something with that risky a return until the average human lifetime is at least 1/4 of the one-way trip time.

RTG's won't cut it over that sort of time frame; isotopes with long enough half-lives to be useful at the end of the trip probably won't have enough average power. I don't have any clue if we can even theoretically build a fission pile with a high enough reliability to be fully-functional over more than 1,000 years. Fusion has similar problems, but at least we know we can store deuterium for long periods of time safely.

42:

Err, IMHO the vestibular and the cardiovascular system might not be so much deconditioned, but just plain different, with unpredictable consequences.

E.g. there are some reports of anosognosia or the inability to sense illness getting better after vestibular stimulation.

http://www.ncbi.nlm.nih.gov/pubmed/3501552

I don't know how the current state of affair is in this, but if this holds up, it might imply that the vestibular system is implicated in body image in relation to self and enviroment.

On the other hand, baroreceptor or related signaling might have unexpected roles in the cardiovascular system.

http://www.ncbi.nlm.nih.gov/pubmed/11458701

One of the things that seems interesting is 'blunted baroreflex-mediated activation of both renal and lumbar sympathetic nerve activity'. If this generalises to other kinds of renal sympathetic nerve activity, that might have interesting results.

http://en.wikipedia.org/wiki/Misattribution_of_arousal

43:

At the risk of becoming even more tiresome, here is a design for a H-B11 fusion rocket with: 100MW total, 51MW thrust, 1.4E6s Isp (1.37E7 m/s effective exhaust v), 33 tonne mass, 28N (2.87 kgf, 6.3 lbf) thrust, 2mg/s mass flow rate (64.6 kg/yr) (assuming I haven't messed up the math again).

Using the rocket equation, given a v_e of 1.37E7 and a mass ratio of 1.5 (1/3 fuel, 2/3 craft; v_0 = v_f = 0) the top speed is a bit under 0.01c. With a mass ratio of 10 it's a bit over 0.05c. A moderate v of 0.03336c (1E7 m/s) is possible with a mass ratio of 2.08 (52% fuel, 48% craft). If 28% of the dry craft mass is engines, then this speed should be achieved in about 1000 years. The engine needs a thrust/weight ratio at least 10x higher with the same Isp to make a generation ship plausible.

44:

Of course, on a multigenerational flight, the cultural effects of this might be very interesting, let's get a little bit biologically deterministic; the changed experience of body and emotions could change the general way this society would look at these things; some people might keep to the old way and use exercises or drugs to achieve that, if the colonists accept the changes, they might keep to the 'spacer' way by related measures when they finally reach a one-g-planet.

There is a theory that some high-risk sports, loud music and like (and some kinds of speculative fiction) owe their popularity to the fact they give a excitement rare in our modern society. Maybe our colonists have similar ideas. ColonPunk, anyone?

45:

Well, one year, as given, no?

46:

The crew were still able to tell the ground staff what was wrong -- they had lost power and CO2 buildup was going to kill them. They were going to die. The fact they were comunicating with the ground staff meant they could tell them what had happened, if not the exact proximate cause. As a bonus the ground staff found a solution to the killing problem, the CO2. They couldn't fix the exploded oxygen tank (it was a spark from the wiring to the stirrer unit, not a defective safety valve) but the crew being able to tell the ground staff what was killing them led to a solution.

Your original comment suggesting that a starship suffering a lethal problem in flight and being in communication with home wasn't going to be of much help. The one similar case we know of in the history of spaceflight the death of the crew was actually averted by communication with home.

47:

how come noones mentioned the dyson sphere?

Because we're discussing the feasibility of a steam engine for raising water from flooded mine-shafts by means of a fire, and you're jumping straight to asking about nuclear powered submarines.

48:

More likely a "standard" gigawatt fission reactor similar to the ones we ought to be building more of here.

Possibly a Thorium pile, possibly a fast reactor, and perhaps with a certain amount of cleverness around gravity involved. Submarine reactors are expected to stay the right way up AFAIK, but the AGR is presumably less dependent on gravity than a PWR or boiling water reactor.

49:

BTW, are there any design of standard or more exotic fission reactors working in zero-g around?

One problem I can think of is that safety measures like free falling cadmium rods to stop runaway nuclear reactions might not work there. The Comstar design looks nice, though if other designs work is up to question.

50:

The Soviets flew radar observation satellites with small fission reactors on board. The design allowed for the reactor to be detached and boosted into a higher safe orbit at end-of-life. This didn't work for one of them, Kosmos 954 and the reactor re-entered with the rest of the craft over Canada in 1978. Bits were found in various places in northern Canada, most of them still quite radioactive.

51:

I remember this, though I was not that sure if it was not a more conventional RTG.

http://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

Think I will have to go through some of the literature about the reasons behind some of the specifics.

52:

Interesting, was reading about "Schrage Musik" recently:
http://en.wikipedia.org/wiki/Schr%C3%A4ge_Musik

and here is the Dyson quote:
Freeman Dyson, who was an analyst for Operations research of RAF Bomber Command in World War II, commented on the effectiveness of Schräge Musik: "The cause of losses... killed novice and expert crews impartially. This result contradicted the official dogma... I blame the ORS and I blame myself in particular, for not taking this result seriously enough... If we had taken the evidence more seriously, we might have discovered Schräge Musik in time to respond with effective countermeasures

53:

No, it was a fission reactor. An RTG is great for long-duration deep-space probes providing one or two hundred watts continuously but the RORSATs needed several kW of electrical power to run their radar transmitters and for various reasons the Soviets couldn't fit them with enough solar panels to provide that level of power.

The Wikipedia article on Kosmos 954 has some crap diagrams of the satellite and its reactor but it doesn't go into much detail. It's feasible to use a fission reactor to generate thermoelectric power the way an RTG does and obviate the need for coolant loops, steam generators and turbines or Stirling engines to convert the heat to electrical power but I don't know exactly how the RORSAT system worked. As far as I know they were the only fission reactors to fly in space.

54:

Well, there are terrestial RTG in the low KW region, adding to my uncertainty.

http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Terrestrial

If I ever go hippie, one of these for my trailer...

There were other nuclear reactors in space, notably the American SNAP-10A. There may be some info here:

http://www-pub.iaea.org/MTCD/publications/PDF/Pub1197_web.pdf

Concerning experimental reactor types, I especially like the Energy Amplifier...

http://en.wikipedia.org/wiki/Energy_amplifier

55:

This best description I've seen of the bone mass loss and other effects in orbit is that it appears that people age faster in free fall. Or at least, aging is similar to the stresses placed on a free-falling body.

The real problem is that evolution is the universe's worst spaghetti programmer. Systems get copied and mutated and fit together piecemeal until the kludge works in the system it evolved in. Take the kludge out of that system (for instance by putting it in free-fall, or shipping it to another planet) and (like any kludge) if you're lucky, it's partially functional. Trying to make it fully functional isn't a matter of swapping out modules. You've got to re-kludge the whole damn thing.

In other words, I think that it's going to be hard to get humans and other species adapted to free fall. We might be able to do it with some complex prescription of drugs, diet, and exercise, but we're going to need a separate set of these for every species we take with us. That's a lot to haul along.

56:

If we ever do decide to populate space with habitats and the like the lessons we learn doing that will go some way to helping design a generation ship. Such a vessel is pretty much a huge self sufficient habitat with a destination in mind.

57:

Such a vessel is pretty much a huge self sufficient habitat with a destination in mind.

Close, but not quite on target.

A space habitat in our solar system can count on trade -- there are other people to talk to and buy stuff from and sell stuff to. Physical manufactured product sales are problematic even at interplanetary ranges, but IP and brainpower is a lot more fungible.

A generation ship, in contrast, is going somewhere where there's no technical support and no fallback position and no-one to answer an SOS call. It has to take its entire manufacturing and research and development tail along for the ride.

So our minimal assumption is that a generation ship needs to be a bit more complex than a mere in-system space colony. (And that's hard enough to begin with.)

58:

@ 15:

If practical fusion never arrives, then interstellar colonization by unmodified mark one humans is probably off the agenda, permanently. (You can travel fast, which takes a buttload of energy, or you can travel slow, which takes less ... except you've got to carry an energy source in order to stay warm and grow crops.

So what's nuclear fission, chopped liver? I've always wondered why Blish had his Okie cities powered by fission, given that he had no problem positing what we would consider extremely advanced tech like gravity control, ftl, practical immortatility, etc. He had to have known about the speculations of controlled fusion when these stories were written (iirc, he had something called a Bethe blaster which induced some sort of fusion reaction deployed at least once and considered an immoral use of weapons); it would be interesting to know if he was an early adopter of the Real Soon Now jeer.

Anyway, let's do a few BOTEC calculations. As I said, while fission doesn't liberate quite the amount of energy per unit mass that fusion does, it's no slouch either. In fact, fusion is no more than an order of magnitude better at this than fission (more like five or six times rather than ten, but this is just noodling.)

But that's not the end of the story. "Energy density" is a tricky thing, you've usually got to specify some sort of measure it's dense in for the term to have meaning. And while it's true that fusion is ten times better than fission by mass, by volume the reverse is true: 19.1 gm/cm^3 for uranium vs 0.0763 gm/cm^3 for hydrogen. Plug these numbers in, and by volume, a power metal (I love that old anachronism) has over 20 times the energy content that a fusible isotope of hydrogen of hydrogen does; call it 10 times the energy by volume since this is all order of magnitude.

But that's not the whole story, of course. You also have issues such as storage, and while I don't know how easy it would be to store large quantities of hydrogen in space, I'd be willing to bet that something like uranium is far easier to handle (given that it has a not-inconsiderable tensile strength, it can even be used for support.) And uranium makes a dandy shield against garden variety cosmic rays; in general, the effectiveness of a material as a radiation shield goes up with density[1]. Also, it's not enough to look at just the energy liberated, you've got to look at the far more relevant usable energy[2]. In fission, less than five percent of the energy goes into those pesky neutrons; wheras fusion, well, let's look at the wiki:


(1) ^2_1D + ^3_1T → ^4_2He(3.5 MeV) + n^0(14.1 MeV)

(2i) ^2_1D + ^2_1D → ^3_1T(1.01 MeV) + p^+(3.02 MeV) 50%

(2ii) ^2_1D + ^2_1D → ^3_2He(0.82 MeV) + n^0(2.45 MeV) 50%


Unless you're willing to go with something more exotic than D-D or D-T, a lot of the energy is expressed in the kinetic energy of the neutron fragments. Not good.

There are lots of other pros and cons in there of course which can be researched or ad-glibbed to your heart's content, but it looks to me like good old fission would work perfectly fine for an interstellar ark type of vehicle. The biggest penalty fission suffers is in the direct mass of the fuel, which I would imagine to be a rather unimportant fraction of the total mass - without any more attempts at calculations (they're effectively meaningless without a lot more inputs), I'd say maybe 10^7 kg of uranium figured into a ship massing at least 10^12 kg. An admittedly WAG, but not completely implausible, and which makes the point that a difference by a factor of ten in the amount of fuel carried is lost in the noise.


[1]IIRC depleted uranium is a much better radiation shield than lead, something like a factor of five. Of course, this isn't depleted uranium, so you'd better check this one out very carefully . . .


[2] Using yet another criterion for energy density while the reaction products for fusion are more energetic per unit mass, individual fission reactions are more energetic per reaction. And of course, the observation is frequently made that even the center of stars like the sun, the amount of energy produced per cubic centimeter by fusion is rather less than what is generated by the human metabolism. One writer noted that a Roman galley full of slaves would produce more energy just by sitting still at their posts.

59:

I really don't think its at all likely that mark one humans will ever go interstellar. Even intersolar colonisation looks dubious but is more likely to happen.
If you want to go to the next Star along then I feel that strapping an AI to a great big rocket and firing THAT into space is probably more feasible. I'm aware there are several can's of worms with that one, but I think it's probably the best chance of getting terrestrial intelligence ou that far

60:

Depleted uranium is perfectly usable as fuel for a fission cycle -- just as long as you use it as cladding around a fast breeder and have the infrastructure to reprocess it, extract the Pu, and use that as your primary fuel. Hmm.

61:

@ 60:

Depleted uranium is perfectly usable as fuel for a fission cycle -- just as long as you use it as cladding around a fast breeder and have the infrastructure to reprocess it, extract the Pu, and use that as your primary fuel.

In the light of something I've read recently, I was thinking more about it's efficacy as a shield, given the ambient radiation levels travelling at one percent of C. Unintentional activation your fuel could be nasty.

The other point about fission tech is that compared with it's competitors, it's likely to be a relatively simpler system and easier to maintain as well. I don't imagine that you necessarily want advanced tech for these sorts of missions, what you want is reliable, rugged, easily serviced tech. Also, given the size of the crew, you've only got so many skill sets available and it's not immediately obvious to me that a working knowledge of practical nuclear fusion will be needed at journey's end.

62:

Maybe I should be a little clearer on my concerns about using uranium - depleted or otherwise - or thorium, etc if you're going to use these kind of materials as shielding from the interstellar environment:

What happens when these metals are activated by the sorts of radiation you are apt to find (or are unlikely to find but still possible to encounter?) Because you don't want your technology to just be rugged, reliable, and easily maintained; above all, you want it to be safe. It strikes me that using water/ammonia/methane ice (as one way to store the necessary hydrogen and keep an elemental reserve on hand) would be a lot safer in this respect since it would be made out of low-Z, nonfissile elements.

63:

@ 43:

Using the rocket equation, given a v_e of 1.37E7 and a mass ratio of 1.5 (1/3 fuel, 2/3 craft; v_0 = v_f = 0) the top speed is a bit under 0.01c. With a mass ratio of 10 it's a bit over 0.05c. A moderate v of 0.03336c (1E7 m/s) is possible with a mass ratio of 2.08 (52% fuel, 48% craft). If 28% of the dry craft mass is engines, then this speed should be achieved in about 1000 years. The engine needs a thrust/weight ratio at least 10x higher with the same Isp to make a generation ship plausible.

Since this is a generation ship, why would you want to go faster than ~0.01 c anyway? You still have to worry about maintaining a closed, viable ecology anyway (it's not like the crew are going to just hop out of the landers and start planting crops when they reach their destination), and with higher speed comes more headaches associated with the interstellar environment as well as less room for Other Stuff. How much more of a problem high speed will be and how much less stuff you can carry is debatable, of course.

64:

One problem I have with all these comments is that they assume that the people who like to live in the space habitat are going to want to leave when they "get to the end". To me this seems unlikely.

Because of this I'm quite happy with very low speeds (gravity by spin). And *more-than-happy* because I think they're going to want to move slowly enough to get from rock to rock, and mine as they go. This, of course, means that they need to be able to use the things they find on those rocks (methane, largely, I'd guess) as fuel. So they'll need some way to run fusion. I can believe in super-capacitors of sufficient quality that they won't need to cart the fusion generators around as they explore, so they won't need much of things like cadmium. CHON atoms are easy to come by in comet heads, but the others are scarcer. Eventually they'll need to find a rocky planet so they can build another habitat, and expand their population.

I don't know WHAT social system would be stable with this kind of life. I can list a few characteristics:
1) There isn't that much benefit in being at the top. But there's some. You don't want too much social tension, but you need enough to maintain quality.
2) Except when building a new habitat, the population is going to be rigidly static. This will be enforced in a way that makes China seem liberal.
3) Political dissent will be thoroughly suppressed. (Not necessarily strongly suppressed. Free speech is quite likely...but even there there will be limits that cannot be transgressed, even in "private".
4) What Charlie has called "sparrow fart security" will be in place.

This doesn't fit with ANY social system that people have so far devised.

Additionally I'll speculate that longevity treatments will be available and widely used. Older people are generally more in favor of maintaining the current social system, so a more elderly population decreases political upheaval.

65:

Slowing down a generations ship is also problematic. The ship is very old, it's low on fuel and it's suffering from radiation damage. One way to fail this mission is that you start to stop your ship and it snaps in two. You need spare parts and structural support for the vessel, increasing ship's mass even more.

66:

Additionally I'll speculate that longevity treatments will be available and widely used. Older people are generally more in favor of maintaining the current social system, so a more elderly population decreases political upheaval.

That's changing one of the parameters; it's not a generation ship any more if the crew who were young at launch are alive when it arrives at the destination 500 years later. (We humans tend not to be able to build social structures that endure for much longer than our own life expectancy. But building ones that need to endure for less than a human lifespan is fairly common.)

Confession time: changing the parameters for humanity makes solving the starship problem relatively easy (or at least "less difficult"). On my to-do list for 2011-12 is the space opera set in the universe of Saturn's Children, some thousands of years later, by which time it's a genuine interstellar civilization -- albeit limited to fractional-c velocities. That's because those folks don't suffer from most of our problems wrt. vacuum exposure ...

67:

@ 64:

One problem I have with all these comments is that they assume that the people who like to live in the space habitat are going to want to leave when they "get to the end". To me this seems unlikely.

For me, the biggest problem is one of ethics. It's perfectly okay if you want to board the ship; that's your choice. But bear in mind you're also making the choice for your children and in all probability your children's children's children.

Speaking as someone who was under considerable pressure to conform to parental expectations, this is most definitely Not Cool.

68:

A molten cloride-salts reactor and a fairly modest inventory of plutonium should allow you to get total burnup of abritiary amounts of DU, but of course at this point you are slowly cannibalizing your radiation shielding for power, and the part where you have to strip down the reactor core every couple of centuries and recondition the materials due to neutron poisoning should be.. Exciting. (and likely to apply in spades to a fusion plant as well!)

Honestly, I am not at all sure that a generation ship is, in fact, any easier to build than a dyson swarm. At least at no point during the building a dyson swarm are you asking people to run off and try to replicate your technosphere in miniature

I would say that the most technically reasonable way to power a starship is probably by beamed power from home, of course, this assumes a power supplier stable over centuries, but the ability to sustain projects over the long term is a prerequisite for /any/ generation ship design, so this presents no difficulties that dont need solving regardless.
..there is, however the slight catch that a laser array capable of moving generation ships around at reasonable velocities and distances starts to look a heck of a lot like an embryonic nicol-dyson beam, so there is a non-zero chance of getting a strongly worded cease and desist from the ISSNWA (Inter Stellar Solar Non-Weaponization Agency) >,)

69:

But then, of course, there is the case of these nice fishes that had fleshy extremities and a way to survive in low oxygen concentrations by way of a certain protrusion of the intestine; both not really that obvious for marine dwellers, but in some rivers in the Devonian...

http://en.wikipedia.org/wiki/Sarcopterygii

And then, there are those mice gaining trichromatic color vision in one generation.

http://www.ncbi.nlm.nih.gov/pubmed/17379811

Though it may have happened before...

http://en.wikipedia.org/wiki/Evolution_of_color_vision_in_primates

In some ways, as reformed treehugging monkey I think we're quite well suited for zero-g, though I somehow miss my manipulating tail. If some of the less extreme ideas about aquatic apes apply, that's another thing, though I'm thinking more along the walking on the shore than about the swimming on the high seas line.
Oh, and my opposable big toes on my feet, concerning the things I miss. Problem is, we will only know afterwards how we're adapted for space.

70:

Well, there have been some experiments...

http://en.wikipedia.org/wiki/Moriori

Two things strike me as especially interesting; first of, it took quite little time, like about a few hundred years, to establish the two very different cultures of Maori and Moriori, which are in terms of violence on the two extremes of human populations.

Second of, the notorious bad ending...

71:

"It's perfectly okay if you want to board the ship; that's your choice. But bear in mind you're also making the choice for your children and in all probability your children's children's children."

You could probably make the same argument about living in N. Korea.

72:

So we need a new version of BioSphere 2, in space.
The history of that project is fascinating, not just what happened to the Oxygen and Carbon Dioxide balance, but the psychological effects. Jayne Poynter talks about it at TEDxUSC:
http://www.ted.com/talks/lang/eng/jane_poynter_life_in_biosphere_2.html

73:

You've got to build a generation ship that is a place that people would want to live in even if it was just sitting around at L2. This solves the problems of getting people to volunteer to test it and the moral issue of not giving the next generation a choice (they don't ever get a choice anyway, but maybe the ship is a better place to live than an overcrowded Earth?) And then you get to say that the star you're aiming at isn't your destination - just your first port of call.

74:

@ 72:

This solves the problems of getting people to volunteer to test it and the moral issue of not giving the next generation a choice (they don't ever get a choice anyway, but maybe the ship is a better place to live than an overcrowded Earth?) And then you get to say that the star you're aiming at isn't your destination - just your first port of call.

That strikes me as solving the ethical problems of AI by labeling whatever machines do as "not really thinking".

No matter how complex the task these machines perform, say being an effective Jeeves to humanity at large's Wooster. "Sir, might I suggest having that much plutonium in a single location would be couterproductive to Aunt Dahlia's Midsummer Auction for Charity? I also have it on good authority from Spode's man that the jacket you have selected for the event - the silver one with the gold convector fins - is precisely of the cut and style that gentleman will wearing."

75:

Having a trip take several thousand years rather than several hundred greatly increases the chances of something bad happening (social, biological or mechanical) that kills the colony.

It also makes it more difficult to stock enough of certain consumables that either can't be effectively recycled or for which recycling is less than 100% efficient. These latter items tend to be lost exponentially, so a 10x longer trip would have an 1/n^10 larger initial supply requirement. If n is 0.9999, it's not a problem, but for some things n is likely much lower: helium, rare elements, or thermosetting polymer feedstocks for gaskets, for instance.

76:

Define "overcrowded earth".

If we populate the whole damn surface of the planet to the same density as Manhattan or Hong Kong, we'll have on the order of 0.5-2 trillion people -- but it's still possible to have a good quality of life in Manhattan or Hong Kong.

People are very compressible; while folks one generation away from tilling the soil might consider megacity living densities to be abhorrent, those of us who didn't grow up down on the farm often like city living.

Whereas a generation ship is most likely to resemble small town living -- unless it's big enough to support a population of over half a million people.

77:

SoV - In case you didn't catch it, I responded to your request for history books here.

78:

I'd strongly suggest that

a) you go back and look at the time scales associated with those adaptations you are talking about. I'd suggest reading Peter Ward's Out of Thin Air as a start.
b) especially look at the evolution of lungs with more care. Swim bladders in modern fish are former lungs, and rather than being adaptations for a riverine environment, they were adaptations for an ocean that was largely anoxic (as is today's Black Sea). Sea oxygen levels varied widely in the paleozoic and mesozoic, and low oceanic [O2] is probably why there were more air-breathing aquatic reptiles and far fewer sharks and big fish than there are today. As I said, go back and look at the time scales involved, if you think these adaptations are trivial.

b) go back and reacquaint yourself with the fundamentals of space medicine (check Wikipedia). They cite a 1.5% loss of bone mass per month of freefall (in agreement with at least one other reference I have), especially from pelvis, femur, and lower vertebrae, and the calcium outflow is sufficient to make kidney stones a real hazard. It's not clear whether any exercise regimen is sufficient to halt the decline, nor is it clear whether any osteoporosis treatments are effective. Pelvis and lower vertebrae, incidentally, don't simply hold you up under gravity: they are near your center of mass, and any full-body motion is going to involve those bones. Breaking them isn't a good option.

And that doesn't deal with the non-trivial problem of radiation that the others are talking about.

So no, I don't believe that humans will adapt to long term free fall automatically.

79:

Biosphere 2 is a pretty strong argument for not bothering at all. The messed up situation with Biosphere 2 is also revealed here:

http://en.wikipedia.org/wiki/Biosphere_2

Instead of L2, Charlie, I'd suggest dropping the thing in the ocean. Lots of good science can happen down there, and getting the test subjects back to terra firma when things go pear shaped would be easier.

Of course, no space nut will ever go for that. The Abyss just isn't as sexy as Star Trek.

80:

Or some people reproducing in general...

http://en.wikipedia.org/wiki/Rainer_Schaller

http://de.wikipedia.org/wiki/Siegfried_Borchardt

Well, one of them is an inhuman asshole, and the other one gets my vomit, err, just who's who...

SCNR.

81:

Eh, for saturns children, it should possible to travel to anyplace where you trust the natives at light speed - tough, given the tendencies of said civilization towards enslaving people, I can see why communication-laser star travel might be *much less* popular there than in other settings where it is an option.

82:

Shh! No spoilers, please (especially for a book I haven't written yet ...)

83:

u know i was browsing through a book about extreme environments at a book store,
once and i read that astronauts after spending a certain amount of time in space
can't stand up for long periods of time right upon their return, is this true?

84:

@ 75:

Having a trip take several thousand years rather than several hundred greatly increases the chances of something bad happening (social, biological or mechanical) that kills the colony.

Could you elaborate? I don't see this as a given, but perhaps my assumptions are different from yours.

It also makes it more difficult to stock enough of certain consumables that either can't be effectively recycled or for which recycling is less than 100% efficient. These latter items tend to be lost exponentially, so a 10x longer trip would have an 1/n^10 larger initial supply requirement.

As a mathematical statement, this simply isn't true(assuming I'm understanding you correctly.) Let me work an example. Suppose you need, say, Carbon-14 which you will lose over the course of the journey by exponential decay (per your claim) even if it is never taken out of it's original container. Now, Carbon-14 has a half-life of about 5,000 years, so over the course of a 100-year journey, if you're carrying 100 tons of the stuff, you'll still have more than 98 tons when you get to your destination. Now suppose that the journey takes ten times longer; at the end of that time, you'll still have better than 87 tons left. Make that ten times longer still and then you'll only have 25 tons left.

Iow, while your general comment about exponential losses is true in some sense, it matters very much both what the characteristic time is for the losses, and where you are on the specific curve determined by that characteristic time.

If n is 0.9999, it's not a problem, but for some things n is likely much lower: helium, rare elements, or thermosetting polymer feedstocks for gaskets, for instance.

See above. Also, you've used an invalid argument form, that is, you're not saying that "we know X will be needed, it has characteristic time Y which means the trip can't take any longer than T", you're saying what if that is true. While apparently similar in form, they are in actuality far different. See my usual rant about burden of proof requirements for why this form is invalid.

85:
So no, I don't believe that humans will adapt to long term free fall automatically.

Neither do I, I just think that even if we haven't evolved in a free fall environ, we might have a better
chance at adapting to it than some other organisms; the main problem is to avoid unwanted optimism, but then, excessive pessimism might be unrealistic, too.

That's why I mentioned preadaption, or, to avoid any teleological implications, co-option.

http://en.wikipedia.org/wiki/Preadaptation

First of, there are some structures on a species level that can be co-opted, second of, who says that some people, like those suffering from orthostatic intolerance on earth, won't fare better than others.

In some areas, it could be worse for humans, e.g. we could use geotropism in some systems we don't.

On another level, even though developmental biology is THE area of genetic determinism, some of those systems are quite adaptable; the neuronal system of mice learned to interpret the signals from an additional cone in one generation, there were no other modifications involved, just ONE mutant protein.

I agree that evolution normally works on a much grander time-scale, though sometimes also in the space of a few generations; note also that even with a long evoltuion, there are no 'perfect' organisms, in some way birds are better adapted for living on land than us, see breathing and excretion.

In retrospection, I think we might be in for some pleasant surprises, though how this relates to the shitload of trouble we're about to get is up to question. According to some, Drosophilas may be quite apt at adapting to gliding in microgravity, that doesn't change they die like, well, the flies in microgravity...

86:

Solve the propulsion/energy source issues and there is still another issue.
You have a minimal ecosystem. Also a minimal number of colonists (well, ancestors of the prospective colonists). Let's say you treated the original generation to kill all harmful bacteria and accessible viruses before boarding. It isn't going to take long before some commensal bacteria mutate to fill now-empty niches and some of these will be pathogenic. Ditto potentially for the viruses carried in our genomes.
Drugs are a product of a rich and varied ecology. Our ship's small stock of antibiotics is going to become useless soon after the start of the voyage (bacterial evolution) and there aren't going to be new drugs (no raw material). Since the pathogens will be on the ship and any potential treatments back on earth, there won't be a way of testing alternative drugs for efficacy.
Result: plague ripping through a small gene-pool. All we need is a new form of VD causing eventual sterility to end the grand experiment early. Don't forget, TV/movies are unlikely to appeal (after a while ship culture will have diverged to the point where Earth-based references are too much like hard work) so guess what the most popular "entertainment" is likely to be once again?

87:

That's why the folks on the space station spend so much time each day exercising. They don't have gravity to work against and if they came home without exercising at all, they would have to be carried. With the exercising, they may need help, but it's not as bad.

88:

The more I think about the engineering (physical and social) problems of interstellar voyages longer than a century or so, the more I think that we're looking at the wrong model for colonization if we want to send Mark 1 humans. Instead of trying to go from Star A to Star B in one shot and colonizing only the inner solar systems of those stars (think of the colonization of North America by European nations by going all the way across the Atlantic on each trip), we should take the model of the settlement of the Pacific by island hopping instead.

For this to work, we have to assume that the Kuiper Belt, the Scattered Disk objects, and the Oort Cloud have approximately the positions and composition of the current theory (only a few candidate Oort Cloud objects have been observed as yet). The Kuiper Belt is a torus extending from about 30 AU (the orbit of Neptune) to 55 AU from the sun and over 10° above and below the Ecliptic. There may be as many as 70,000 Kuiper Belt Objects (KBOs) of greater than 100 km diameter. Total mass is predicted to be 20-200 x the mass of the asteroid belt, primarily frozen ices such as water, methane, and ammonia.

The Scattered Disk is much less dense volume beyond the Kuiper Belt out to about 100 AU (these objects are theorized to be KBOs whose orbits were modified by interaction with Neptune or one of the other outer giant planets. They have highly eccentric orbits which may also be highly-tilted to the Ecliptic.

The Oort Cloud consists of an inner torus (called the Hills Cloud) lying between 2,000 and 20,000 AU and an outer sphere lying between 20,000 and (between 50,000 and 200,000 AU). The edge of the outer cloud is at the surface where galactic tidal forces and the gravitational fields of other stars can perturb orbits away from the sun's gravity. It is estimated that there are as many as 1 trillion Oort Cloud Objects (OCOs) larger than 1 km in diameter, and many billions with diameters of 20 km (on average the latter are 10s of millions of km apart). OCOs are apt to be largely frozen ices, but there may also be rocky objects as well.

What do we need to colonize these objects, assuming that we intend to "live off the land", getting all consumables and energy locally? The good news is that there are a lot of volatiles out there, so air, water, and CHON elements for food are available. The bad news is that there are a lot of volatiles, and probably not a lot of fissionables, so we'll need to have practical fusion reactors. On the other hand, we don't have the long time-scales that are required for generation ships, so maybe rebuilding reactors every so often isn't a problem.

The best strategy I can think of for long-term colonization is to stage the travel by sending large groups of people and equipment on something as big as the generation ships but for much shorter travel times. Start with the KBOS: send a ship out to Pluto or Eris (perhaps eventually one to each). Given something like a VASIMR drive it should be possible to get there in 2 or 3 years1. Carry enough equipment to construct smaller ships for the colonists to use to get to other KBOs in the immediate vicinity (with VASIMR again they can go from Pluto near aphelion to either edge of the belt in less than a year). After a few widely separated base areas are colonized the rest of the Belt can be colonized stepwise from existing colonies.

Getting into the Oort Cloud takes longer, even starting from the outer edge of the Kuiper Belt (assume the Scattered Disk is too thin to bother with initially; it might be colonized when the Belt is thickly settled). But if we can build a ship that can achieve 0.01c, which we assumed could be done in order to send a generation ship to another star, then getting to the inner cloud takes about 3 to 4 years, and then we can do the same stepwise colonization.

1. I'm assuming optimal specific impulse of 5,000 (current target for operational VASIMR drives) to 10,000 seconds. Propulsion systems that can do better obviously take less time.

89:

I disagree.

A spaceship can be throughly sterilized with hard radiation before setting off and the people that come on board can be ascertained to have nothing but essential gut bacteria. I suppose something could mutate from that, but consider that hunter gatherer groups have hardly any epidemic desease, it takes large groups of humans living in close proximity to animals to produce the necessary desease incubator. Also, if you think about it, we didn't have antibiotics till the 1940's but didn't die out. There are always ongoing cleanlinessprecautions. Eg. all air is zapped with high energy UV rays before it's recirculated.

As to the entertainment, Romance of the Three Kingdoms was written by another race on the other side of the world, half a millenium ago and espouses a pretty ailien(to most westerners) cultural mindset, but it's still a damn good read. The colonists would not be bored.

90:

To be fair, Charlie, there may be some very large diseconomies of scale in building cities that large. Not to mention the loss of the supporting ecosystems.

I don't think Mike meant "overcrowded" in the literal sense of "no living space."

91:

There are two arguments here.
1.) longer journey = greater probability of colony-killing things happening. Obvious. Otherwise one would have to claim that the odds of catastrophic failure are non-monotonic. (i.e. a 5000 year mission is less likely to fail than a 500 year mission.)

2.) Exponential decay of consumables. I'm not saying "what if". The journey length is known in advance. "you're not saying that 'we know X will be needed, it has characteristic time Y which means the trip can't take any longer than T'" No, that's exactly what I'm saying, combined with the error bars in the projections of consumable needs, multiplied by the count of characteristic times (with their own, larger and compounded error bars) over the journey period for the critical path supplies and the finite load-carrying capacity of the craft, these taken together imply a maximum practical journey length for a given acceptable probability of failure. That just allows for "known unknowns". "Unknown unknowns" add to the risk.

92:

Readers thinking, readers extrapolating. In blog comments, forsooth. No good can come from that.

93:

@ 91:

1.) longer journey = greater probability of colony-killing things happening. Obvious. Otherwise one would have to claim that the odds of catastrophic failure are non-monotonic. (i.e. a 5000 year mission is less likely to fail than a 500 year mission.)

I find this to be incomplete. You can also argue that shorter journey = higher speeds = greater chance per unit time of catastrophic failure. Does the smaller total time spent justify taking the higher risk per unit time? I don't know. But I do know that it's not automatically a given for each and every scenario of fast/slow pairs.

There is also the untrivial point that the possibility of failure does not end just because the ship finally reaches the target system. If your colony fails because instead of including necessary item A you opted for extra engine and propellant mass, you're just as dead either way. Please bear in mind that this is a one-way trip.

So it does not seem to me that you can automatically assume that faster = better/safer. Me? Until the nature of the interstellar medium is a lot better known, my personal feeling is you don't want to run into anything too fast. And until we get the procedure down pat, I'll also opt for More Stuff over Bigger Engines.

2.) Exponential decay of consumables. I'm not saying "what if". The journey length is known in advance. "you're not saying that 'we know X will be needed, it has characteristic time Y which means the trip can't take any longer than T'" No, that's exactly what I'm saying, combined with the error bars in the projections of consumable needs, multiplied by the count of characteristic times (with their own, larger and compounded error bars) over the journey period for the critical path supplies and the finite load-carrying capacity of the craft, these taken together imply a maximum practical journey length for a given acceptable probability of failure. That just allows for "known unknowns". "Unknown unknowns" add to the risk.

With respect, no, you haven't said that. Go look up at what you wrote again. You have simply said in language that I have made more precise that the characteristic times for the loss of irreplaceable reserves (and you seem to be assuming they can be replaced at the end of the voyage, which is far from certain) can't be much less than the length of the voyage. And certainly I agree.

But noting that this condition must hold is not showing what specific nonrenewables necessitate (much) higher speeds. Using your figures for going five times as fast as 0.01 c, for example, you need six times the mass budget of the entire original colony. Could you please tell me what specific resource you're thinking of that would last 200 years in the smaller, faster ship, but wouldn't last for 1,000 in the slower, but much, much larger one?

That's the question you've got to answer. Specifically :-)

94:

Sorry, but this is not about children conforming to parents expectations. Children were taken on the Mayflower,the Oregon Trail, they were processed through Eilis Island in the millions. It is estimated that 100 million people in the United Stats, 1/3 of the population, descend from some one who was processed through Ellis Island. In effect, each one was a child of someone who made a major decision that effected not just their life but the life of everyone of their descendent's. For ever and ever, Amen.

Ask yourself this, how fair is it to your future children that the decision you are making today, as you fight with your parents over whatever it is you are fighting over, how fair is it to them that their life is going to be profoundly effected by what you decide?

It is called life, you pays your dollar, you takes your chances, and everyone after you lives with the results.

95:

The kicker seems to be the problem of keeping meat alive between the stars.
How about not bothering with that bit? Send starships that are able to set up infrastructure on the target location and then assemble the colonists "from scratch"-- whether the genetic information is stored onboard or transmitted later, along with the information for whatever robo-creche is supposed to raise them.
Sure, the kids'll be a little odd...

96:

@Sacha

No, it's really true. About 50% of first heart attacks are fatal more or less immediately, but 90% of people who reach hospital alive will survive for at least 30 days.

There are at least two contributing reasons. Firstly, some heart attacks cause immediate cardiac arrest, which is typically fatal in real life (in contrast to TV). Properly done CPR within two minutes and defibrillation within ten minutes still only gives you about a 50% chance of surviving to hospital entry.

Secondly, as Charlie suggests, quite a lot of people with survivable heart attacks think they have heart pain or muscle strain and don't go in for treatment. Quite a lot of them end up dead. Don't be like them.

97:

Since this comment has somehow segued into both Saturn's Children and inevitable bacterial colonisation, has Charlie ever explained how they managed to sterilise the Earth in that book? Or was it a case of the remaining humans isolating themselves into pre-sterilised habitats while the robots napalmed the soil and vented the atmosphere?

98:

General comment:
No, it isn't just religious/political dissent that drives people out, nor the desire for greener pastures.
Here is a selected quote from a poem:
"Till a voice, as bad as Conscience,
rang interminable changes
In one everlasting Whisper
day and night repeated -- so:
"Something hidden. Go and find it.

Go and look behind the Ranges --
Something lost behind the Ranges.
Lost and waiting for you. Go!"

So I went, worn out of patience;
never told my nearest neighbours --
Stole away with pack and ponies --
left 'em drinking in the town;
And the faith that moveth mountains
didn't seem to help my labours
As I faced the sheer main-ranges,
whipping up and leading down.

March by march I puzzled through 'em,
turning flanks and dodging shoulders,
Hurried on in hope of water,
headed back for lack of grass;
Till I camped above the tree-line --
drifted snow and naked boulders --
Felt free air astir to windward --
knew I'd stumbled on the Pass.

'Thought to name it for the finder;
but that night the Norther found me --
Froze and killed the plains-bred ponies;
so I called the camp Despair.
(It's the Railway Cap today, though.)
Then my whisper waked to hound me:
"Something lost behind the Ranges.
Over yonder! Go you there!"

The author's initials are R.K.

@21 & Charlie
Heart attacks - remember, you are probably talking abour Glaswegians, who are "aw reet, Jimmie!", wouldn't DREAM if going near a doctor unless they actually BROKE something, and are probably (ahem) living on deep-fired Mars Bars. US readers should ignore this section of the post, as it contains unique local cultural references.

SoV @ 67
BUT
ALL the choices all of us make, all the time, are not just for us, but for our children and their descendants.
It was always this.
What's new?

@ 70 Maori / Moriori
My wife comes from NZ.
When the Maori "activists" start going on about the "unequal" treaty of Waitangi, the way to shut them up is just to say; "Moriori". They don't like it up 'em Captain!

Charlie @ 76
Nice try - I saw you palm that card!
You've still got to FEED them, you've still got to have a suitable area for food-production, and that must be varied.

@ 97
It was a MacGuffin (I think)

99:

Hi Guys
Of course if we're robo-creche raising babies we might as well go the whole hog and tissue-engineer new bodies for adults scanned to a (yet to be determined) sufficient fidelity. I am sure many would happily volunteer to be beamed in such a fashion between the stars - even if the scanned "original" (says who?) stays at home.

100:

Eh? It was explicitly stated that after the extinction of biological humankind the robots stopped paying any attention to enviormental laws, burned every scrap of coal, gas and oil available and tipped global warming into "oceans start boiling" territory. I am not sure if this was deliberate malice or just carelessness, because nobody onstage in the book was in a position to know.

101:

Very true, but perhaps thats part of the answer as well? If we develop a sizable amount of habitats in various places around the system (different orbits, lagrange points, around different planets) then over a long enough time (perhaps hundreds of years) we could map how the habitats interact and survive. The lessons we learn could result in us essentially taking the best bits of each habitat and how they support each other and bolting them together at a considerably closer distance (i.e. attached together) before cracking a champagne bottle and sending it off.

What i've always wondered about generation ships though is how popular they would actually be? It strikes me that confining yourself to one place for the rest of your life on the understanding that your childrens, childrens, childrens.....child will eventually get somewhere is eccentric to the extreme. Im not saying that people won't do it but what happens if the 4th generation recieving reports from Earth and watching old Earth media decide they want to turn the ship around and head for home?

Then there's the unsettling idea of setting off at 1% C and arriving at your destination 2000 years later only to find that that 1000 years after you left a better ship travelling at 40%C set off. It would arrive in just 50 years and have had over 900 to build up a society in your promised land

102:

1. Radiation sterilization at a level that will eliminate all bacteria is likely to affect organic compounds including plastics and other materials used in the construction of our hypothetical generation ship.

2. "Essential gut bacteria" -- we don't know what the minimum set of gut bacteria required to healthy digestion looks like, but going by the range of gastrointestinal commensals we carry, it's going to involve several thousand different species, including fungi and protozoa as well as bacteria. There's some work that indicates many modern autoimmune problems -- from asthma to multiple sclerosis -- can be mitigated by exposure to antigens in childhood, or even by parasitic worms; and then again, some of the commensal gut bacteria we carry can become pathogens under the right conditions. (For example, E. Coli is ubiquitous and harmless -- most of the time: but some strains cause violent diarrhoea, and it's not immediately obvious how to prevent these from re-emerging.)

3. You missed out on our skin culture, which -- again -- interacts with our immune system and may well have some useful functions we're unfamiliar with; if nothing else, the presence of a stable skin microecosystem means that alien heterotrophs landing on an otherwise free buffet lunch table (the human epidermis) are going to have competition that has already learned not to eat the table cloth.

4. You also missed out the full range of stable gut bacteria carried by the worms that aerate the soil in the on-board farms, or the other mammalian species on board (if you're planning on colonizing a planet you want to be able to seed a stable terrestrial biosphere, which means more stuff than just H. Sapiens Sapiens).

5. You also missed out the human endogenous retroviruses that are hitching a ride on our chromosomes but which, under the right conditions, may get shaken out, produce capsids, and go walkabout.

6. As for your point about antibiotics and our lack of them prior to the 1940s, are you aware that circa 1940 infectious disease killed roughly 30% of us, about the same as cancer in the developed world today? (Would you like fries with that fulminating wound that is beginning to stink up the isolation ward?)

Here's the point: viewed at a cellular level, human beings are ensemble superorganisms composed of collectives of specialized tissue composed of eukaryotic clones, operating within a complex biosphere that they've coevolved in. Bits of the biosphere interpenetrate these superorganism collectives, moving in and out via the external or internal interfaces (the epidermis or the gastrointestinal tract). The superorganisms are nourished by -- and provide nourishment for -- other components of the larger biosphere.

The ensemble can continue to function normally for a while when removed from the biosphere if its nutritional requirements are abstracted along with it and the environment mimics the biosphere -- correct gas composition and pressure, correct temperature range -- and it is given access to food and waste products are removed. But all this amounts to is a transient buffer; the organism can't function in isolation without a supporting biosphere for any extended length of time.

103:

The kicker seems to be the problem of keeping meat alive between the stars. How about not bothering with that bit? Send starships that are able to set up infrastructure on the target location and then assemble the colonists "from scratch"

That may actually be harder than keeping the meat alive. Doing it properly requires the whole mind uploading (and then downloading) shtick to be worked out; alternatively, raising and socializing a human child from scratch -- even if you can ship frozen fertilized ova and have the medical tech to run an artificial uterus for nine months without a hitch -- would appear to require a human equivalent artificial intelligence for the child to interact with; learning isn't a deterministic or mechanical process.

In the terms of my earlier discussion of interstellar colonization, I classify all these technologies as "magic wands": FTL propulsion, mind uploading, true general AI. Any one of them radically alters the picture for interstellar colonization, and makes it a lot easier. On the other hand, I find easy questions less interesting ...

104:

Actually, it was authorial fiat: I just wanted a sterile Earth. However, runaway heat pollution will do that. C3 and C4 plants tend to stop photosynthesizing somewhere between 36 and 50 celsius. Mammalian metabolism relies on enzymes that denature somewhere above 45 celsius. (We're already looking at a late 21st century where heat waves will push large areas of the planet above 42 celsius for protracted periods, which is unsurvivable for an unprotected human. (Note unprotected.))

If you add "cheap(ish) fusion" on top of a planetary greenhouse, you also get waste heat. A robot civilization isn't really affected by rising temperatures the way humans are. So if we go for global warming of 20 degrees celsius by the 23rd century, the planet is going to be -- for the most part -- uninhabitable and we'll kill off most land-dwelling life and most of the life in the surface waters of the tropics.

That's not going to kill off the thermophilic chemoautotrophs colonizing the black smokers, but a radical shift away from a photosynthesis-driven ecology combined with rising temperatures could well have hideous effects in the ocean. I'm particularly thinking of the Permian-Triassic methane event; heating the oceans may cause most of the methane clathrates to decompose, upping atmospheric methane levels by a factor of a hundred, and driving further uncontrollable greenhouse warming. Given a reduction in oxygen in the upper waters (once we've shut down photosynthesis) we may have conditions conducive to a bloom in sulfate-reducing bacteria; that's going to poison everything else (and irradiate land dwellers with UV due to the screwed ozone layer).

Finally, the robots keep dumping waste heat from their reactors into the Gulf of Mexico until it comes to a rolling boil (ha ha, only kidding). By which time there's not a lot of viable DNA or enzyme-based chemistry left except in the deep oceanic trenches and the lithosphere ...

105:

It strikes me that confining yourself to one place for the rest of your life on the understanding that your childrens, childrens, childrens.....child will eventually get somewhere is eccentric to the extreme.

Au contraire: it's how the majority of humanity has lived, all along. The ones who up sticks and move are unusual -- most everywhere on Earth that's inhabitable has had human inhabitants for many thousands of years, so if you want to move, you have to fight the incumbents off their land or bring a way of working the land that permits a higher population density. American foundation myths are an aberration: most people have been born, worked, married, had kids, and died within ten miles of the same spot.

Then there's the unsettling idea of setting off at 1% C and arriving at your destination 2000 years later only to find that that 1000 years after you left a better ship travelling at 40%C set off.

Nonsense on stilts, and easily solved: before you set off you publicize your destination widely so everyone else knows where you're going, and you pack (a) a fast breeder reactor, (b) lots of U238 cladding for it, and (c) blueprints for H-bombs to assemble if, on approach, you spot signs of prior occupation. Anyone who claim-jumps your destination had better be looking over their shoulder for the warheads incoming at 0.1-1% of c ...

106:

Nonsense on stilts, and easily solved: before you set off you publicize your destination widely so everyone else knows where you're going, and you pack (a) a fast breeder reactor, (b) lots of U238 cladding for it, and (c) blueprints for H-bombs to assemble if, on approach, you spot signs of prior occupation. Anyone who claim-jumps your destination had better be looking over their shoulder for the warheads incoming at 0.1-1% of c ...

Just shoot the other ship down with your superior starfaring technology, while it's still 500 years out.

107:

We humans tend not to be able to build social structures that endure for much longer than our own life expectancy.

I'm not sure about this one at all. I live in a social structure that's endured for multiples of my own life expectancy; so do a lot of other readers here. I've worked, studied, socialised and worshipped in social structures which have endured for the same period of time.
And one of the main reasons for social structures not enduring is their being invaded by other social structures, which obviously wouldn't be an option for an isolated generation ship.

108:

So many red herrings there it's hard to know where to start, or whether to bother.

The issue isn't the chance of failure per unit time, but the integral. The chance of failure never goes down, although the chance per unit time likely will. Going from 0.01 to 0.03c should not affect the risks per unit time substantially since collision risk is a minor part of risk, and whether it's 1 ton or 10 tons of TNT equivalent per gram, running into stuff is still catastrophic. Radiation risk shouldn't be too different, either. Nor will going faster require vastly more fuel (~50% of initial mass vs. 33% at Isp of 1.4Ms, as I said earlier).

By having more power density, a higher thrust/mass ratio and thus fewer centuries spent in acceleration, one gets to whatever chosen speed more rapidly and to the destination more rapidly. (That was the only point I had in remarking that 10x better thrust/weight ratio was needed.) If you don't want to get there faster, why do you want to get there at all?

Your last couple of paragraphs are a bit of a straw man- I gave the figure for 0.05c just to show it was unfeasible. I said 1E7 m/s is fast enough for me, but 2000 years of acceleration is not - that was the point of my post. You seem to be saying that 32 micro-g to 3.3E6 m/s is enough acceleration for you, and an average v of half that for 667 years of the trip isn't anything worth trying to improve. OK, but I'd personally rather see if I can get up to a slightly less arthritic 0.3 milli-g and reduce the time to 67 - 200 years acceleration.

I also already gave reasonably specific examples of things that could be depleted over time (light and rare elements, thermoplastic feedstocks.) Genetic diversity for some of the species in the canned biosphere, water loss and soil salinity could also become problems over this span, as could radiator fluid for droplet radiators. There are many things that could be expected to run out or degrade, and addressing one problem will limit the mass available to address all the others. Going 3x slower doesn't help the mass budget much - just 16% of the total.

I'm not going to argue further about this side issue, nor am I going to identify and quantify each of the tens of thousands of types of supplies needed for a starship voyage to be successful which might be expected to have an additional risk of running out because the trip takes 3.3 times as long. What you're demanding seems to amount to asserting that it is fallacious for me to say that that the Earth-price of some unspecified vital commodity or other is quite likely to go up dramatically at some point in the long term, because I haven't specified an absolutely complete model of the world economy which would allow precise definition of the term "vital".

109:

#105 and #106 - Are habitable planets actually rare enough for this to be an issue? Note that "absense of evidence" is a comment on "quality/range of detectors" rather than "evidence of absense" per se.

110:

>You could probably make the same argument about living in N. Korea.

I can't imagine how you could describe being trapped in that dystopian hellhole a choice for anyone but a handful of upper echelon apparatchiks and the occasional western deserter.

Uncertainty over what life may be like on earth in the mid or long term is one of the reasons I am something of an antinatalist, I have no guarantee my great grandchildren won't be living under tyrant director Pecking Pa the eight.

I don't suppose a generation ship would take antinatalist crewmembers, it sort of defeats the point.

111:

>Anyone who claim-jumps your destination had better be looking over their shoulder for the warheads incoming at 0.1-1% of c ...

This scenario sounds similar to the match up between a certain imperial Navy and the festival in Singularity Sky. The claims jumpers are likely to be more technologically advanced than the slowboaters, and ready for them too. Not a pretty picture.

112:

Sorry for the triple, I just recalled another variation on the theme from one of Terry Pratchett's early sci-fi novels, after FTL is invented, the hilariously outdated interstellar ship full of frozen crewmembers is maintained and monitored in it's journey by the spacefaring equivalent of a historical society.

Rather humiliating for the pioneers once they wake up, I imagine.

113:

Charlie @ 104
It's stil a MacGuffin - given the appalling scale of the Permian-Triassic event(s) .....

@ 107
Long-lived social structures.
Universities?

114:

Is L2 in perpetual shadow? I thought that any stable orbit there was a halo with few or no eclipses by the earth, which in any case would have an apparent radius asnearasdammit to that of the Sun.

As for the idea, my money's on reality TV as the driving force. "I'm a celebrity, get me out of here at 0.1%!". Also, although earth can't feed back about imminent technical problems in real time, two, or five, or even twenty years gives you time to feed back about organisational and sociological ones. Something for everyone. Just don't get voted the weakest link. Or lose the 'who gets to deccelerate?' balloon debate at the end of the journey. Or they will turn off the laser...

That's the plot, and anyone's welcome to it. But plots are easy: dialogue is hard.

PS - a recent study on the Deepwater Horizon methane plume implied that (in the Gulf, which might be very different from other seas) it must have been eaten by a massive bloom in the local methane-eating algae. So the runaway clathrates might not be what kills my kids: they (and I) still have to worry about a whole bunch of other positive feedback loops, such as permafrost melt.

115:

Chris Williams @114: You're right: Sun-Earth L2 is not in perpetual shadow - Earth's umbra cone doesn't reach that far. The penumbra does, just about, but that leads to an annular ring eclipse. With the eclipse L2 gets roughly 15% of sunlight the Earth does, so it's equivalent to being between Mars and Jupiter. Halo and lissajous paths around L2 get even more sunlight; the space observatory spacecraft positioned near L2 are solar-powered. Which means it's not a good proxy for interstellar space, either, as it'sha not that cold. The spacecraft have to cool their instruments.

And that's why they call it science fiction. Carry on, all.

116:

Long-lived social structures.
Universities?

Well, yes. But you don't even have to go that far: what Charlie said was that "humans tend not to be able to build social structures that endure for much longer than our own life expectancy". Social structures in Britain alone that have endured for much longer than average life expectancy: a large number of schools, quite a lot of universities, the local governments of most major cities (not London, though), Lloyds of London, several newspapers, the BBC, the John Lewis department store chain, most churches, a fair number of banks, manufacturing companies like ICI and Rolls-Royce... I'm sure that most countries could come up with similar lists.

117:

Put it in the L2 point of the Sun-Jupiter system?

118:

I was watching a show last night about A-10 ground attack aircraft in the first Gulf War. Gen Chuck Horner (who commanded the coalition air forces) was poo-pooing them a bit, commenting that A-10s were something like 5% of aircraft but made up 40% of aircraft losses, and so were too vulnerable to be of much use in the future. That struck me as gobsmackingly stupid, given the inherent danger of their mission.

In this theorizing about habitats/orbitals/ringworlds, has anyone given any thought to the difficulties in getting the water to rotate along with the structure? I imagine you'd have to start with it frozen, or else it wouldn't exactly "stick" to the structure as you started spinning it.

119:

Well, if we're into clondike territory (whoever is on my claim is legit target practive...), to go unwarranted extrapolation here, any society trying extrasolar colonization needs experience with long-term social architectures on their colonization fleet, experience with long-term social architectures implies some of the native society will be modeled along the same lines, long-term social architecture implies sustainability, and sustainability implies ritualization of aggression, both to contain runaway conflicts and to have a way of checking quarrelsome subjects.

If anybody finds this utopian, well, 'ritualized aggression' in this context applies both to Geneva convention and flower wars. And no, flower wars are not some hippie concept from the 60s...

http://en.wikipedia.org/wiki/Flower_war

So, first of, defense against nuclear warheads coming in at a notable fraction of c is nontrivial; second of, shooting of your slowship mates might be an option, it might even be permissable under the term of the faufreluches, it might just be that it is also a nontrivial task (space is huge) and that the legit measures are somewhat limited (using 0.5 c asteroids as grainshot might be legit, fire-and-forget missiles might be debatable); third of, accelerating a nice thermonuclear warhead to 0.5 c is much easier then a accelerating a biosphere, and it is in the vital interest of nearly all parties involved.

This post is dedicated to the buggers on the planet. Their example helped others, there was no way to help them...

120:

True, but are these things relevant to the problem.

They don't provide their own replacements. They all have somewhere for incompatible people to go. They can all do trading with other social units.

121:

Err, and then I meant

any society trying extrasolar colonization needs experience with long-term social architectures on their colonization fleet, experience with long-term social architectures implies some of the native society will be modeled along the same lines, long-term social architecture implies sustainability, and sustainability implies ritualization of aggression, both to contain runaway conflicts and to have a way of checking quarrelsome subjects.

followed bey a

"black is white, and there is a zebra crossing on this motorway at rush hour[1] there...

[1] Yeah, I know, the chances of surviving crossing a motorway at rush hour might be higher than at other times, but let's just assume there is no trafic jam.

122:

While reading through the various comments it occurred to me that it is probably only likely that there will be a major public or private enterprise undertaken when/if a verifiable earth like planet is discovered.
Which leads me to an uncomfortable thought, are humans likely to seize the opportunity of planet hopping as a way of avoiding doing anything about the mess we are making of this one?
If we could move planets would industry/governments care about what they are doing here?

This was in light of what I had been reading about the Kepler mission which was in the news again recently.

http://kepler.nasa.gov/

123:

@114: As for the idea, my money's on reality TV as the driving force. "I'm a celebrity, get me out of here at 0.1%!"

Wonderful idea. Anyone who wants to be on reality TV gets flung out of the solar system at 0.1c. Who cares if the generation ship works or not. :-)

124:

#118 Para 2 - Easy; Put the water in tanks at the hub (you may wish to use spacecraft for this), spin the habitat up a bit faster than you want it, then fill the sumps at the rim, allowing angular momentum to keep the water in place, and minimising the work you have to do to spin up, by not accelerating the water.

125:

#114 and #123 - Can we make that "anyone who has ever been on, or expressed a wish to be on, an artificiality Tv show, including presenters?" ;-)

126:

Despite which, the average corporation has a lifespan of around 30 years; the average national system of government (note: not the nation itself, but a specifically constituted system of control) also turns over fairly often.

What you're looking at -- the universities and Lloyds and so on -- are outliers.

127:

I dunno. If you took the entire population of the world over the whole of human history, I suspect you'd find that the vast majority of them were living under the same system of government as their grandparents. I mean, we're not talking about setting up a 10,000-year Long Now foundation - just building an institution that will last longer than a human lifespan.

128:

If I may au contrair again, I don't think that's an accurate analogy of how people did used to live. I agree thousands of times throughout history people have left to settle other places but the settlement took longer than the journey. People might have spent over a year on a sailing ship but got to spend the rest of their life on a new island/continent. The generation ship is like confining yourself to the travelling part for centuries before you even get to this other island. At 1%C messages from home will catch up easily and those messages might be quite attractive. Whilst you are sitting in a hollowed out asteroid that you will never leave thanks to the whimsy of your great-granddad you can watch and read as the home system behind you progresses in leaps and bounds.

Admittedly an STL deterrent launched before you might work but you may run the risk of bombing the home planet of a system wide civilisation. The rest of them might be a little peeved at the actions of these savage time travellers of the past and decide to teach them a lesson 4th millennium style.

129:

I don't know how rare habitable planets are, or how expensive interstellar spaceships are. I do think that taking old fashioned hydrogen bomb designs and trying to use them to threaten people is an uncertain strategy, as someone may call your bluff, and you've no idea whether they can do so effectively. You can't predict technology that far in advance.

130:
ColonPunk, anyone?

I wince enough when I see a top hat with goggles and brass cogs glued on it, I can't even begin to fathom the millinary indignities you're suggesting :)

131:

@ 94:

It is estimated that 100 million people in the United Stats, 1/3 of the population, descend from some one who was processed through Ellis Island. In effect, each one was a child of someone who made a major decision that effected not just their life but the life of everyone of their descendent's . . .

Ask yourself this, how fair is it to your future children that the decision you are making today . . .

It is called life, you pays your dollar, you takes your chances, and everyone after you lives with the results.

@ 98:

ALL the choices all of us make, all the time, are not just for us, but for our children and their descendants. It was always this. What's new?

Well, I'll certainly admit that what I'm offering is personal opinion, nothing more. But it strikes me that Hannah Connor and her brood passing through the stiles at Ellis Island in 1850 might be consciously making a better choice for her children than Dainial Lynn and his family who she meets as they're going in the opposite direction back to the lands of their ancestors.

Or how about something more science-fictional. You know about some of the crazier plans about an expedition to Mars, right? One of them is that it's a one-way trip - it's cheaper to send a lifetime supply of consumables along with the intrepid explorers than it is to bring them there and back again. Now suppose one of those astronauts becomes pregnant while on Mars and decides to go ahead and have a baby? Are you seriously saying that this is in the best interests of the child? Or that decisions like this should be supported? Because I most emphatically don't (again, I admit that this is a judgment call.)

Now, whether you want to spend the rest of your life on Mars under rather primitive conditions with just seven other people, or whether you think it would be great to seal yourself up in a can with a million times that number and with travel further than 50 kilometers a physical impossibility while living under a totalitarian state (probably with the full panopticon solution implemented), well, it's your life. But I personally can in no way think that these conditions would be superior to the alternative of raising your kids back in the Solar System where they have many, many more options and in all probability vastly greater wealth as well as access to a considerably more sophisticated technological and industrial base.[1]

Iow, and somewhat shorter, immigrating to America out of the ancestral lands is a decision you can make for your children if you have every reason to believe it is a far superior alternative to staying behind. Making decisions for them that suit you but are hugely detrimental to them[2], well, that's just not right. Unethical. And immoral.


[1]Of course, there's always the back story that has to be considered.

[2]I'm wondering if either Jib or Greg thinks it's okay for parents to pray over their children in lieu of conventional medical treatment for diseases like diabetes or for accidents like snake bites? I should probably mention for those that don't already know that I had a personal situation early in life which strongly color my views on the matter.

132:

Charlie @ 126
Outliers, yes, but nonetheless, quite a lot of them, in total nimbers, if not in proportion.
These are the ones you need to study.
Which is part of the question you were asking in the first place, wasn't it?

133:

I find the society question all very interesting - the problem that a generation ship is trying to solve would be comparatively stable, assuming you're not trying to build too many upgrades at once.

134:
...it would be great to seal yourself up in a can with a million times that number and with travel further than 50 kilometers a physical impossibility while living under a totalitarian state (probably with the full panopticon solution implemented), well, it's your life.

Is it just me[1], or does anybody else think about the real world example called 'alternative living in a commune'?

Might be interesting to talk to the parents of your Pippin Galadriel[2] next door. Hilarity ensues.

http://www.18metzger.de/html/letter_II.html

[1] In this context, an mid-thirty biologist with a knack for anthropology, punk and lately appreciating Goa music...

[1] As the man with the hat said, 'your basic hippie is quite predictable'...

135:

@ 101:

It strikes me that confining yourself to one place for the rest of your life on the understanding that your childrens, childrens, childrens.....child will eventually get somewhere is eccentric to the extreme. Im not saying that people won't do it but what happens if the 4th generation recieving reports from Earth and watching old Earth media decide they want to turn the ship around and head for home?

Let me start with your last sentence: not gonna happen. Remember that you start with a certain mass budget (or near-equivalently, a certain dollar amount.) Say you want to take the trip 0.01 c; to get up to speed, your fully fueled vehicle masses perhaps half again it's dry weight. But that's just to get up to speed; to slow down, you need the same multiplicative factor, 1.5, so that the final mass ratio is 1.5^=2.25. Now, if you then want to come back home, you've got to square this as well, 2.25^2 or a final mass ratio of about five. But by allowing for this possibility, your concomitantly replacing Good Stuff with fuel, engines, and extra support. Is that likely? I don't think so. The best bet, imho, is to allow for some sort of reprovisioning and refueling at the destination.

Iow, once they've started, turning back short of their destination is not a physically possible option for the crew or their to-the-nth descendants.

As for you other statement: well, no, for most of history, most people were born, lived, and died without ever traveling further than fifty kilometers from their home. And why would they? Most of the time, such travel was not conducive to your personal health. In fact, it's only been very recently that long-range travel was both desirable in the sense of increasing your (good) options and affordable. Note that wherever these conditions obtained, people were quite content to pick up roots and go.

What would be eccentric would be staying somewhere even when doing so is clearly inferior to the alternative of moving on, or moving somewhere new even though it's not clear why things would be better there and there were some plausible arguments that they would in fact be worse. Iow, the desire to go or stay is situational. Maybe you and yours being stuck in a can 50 kilometers long and 20 in diameter for the next 1,000 years really is the better option.

But that's not the way I'd bet. At least, not without a lot more information.

136:

Im aware of the fuel situation but yes you're right. Unless they had enough fuel to perform two trips (one trip being defined as accelerating and decelerating with a little spare for manoeuvring) they arent stopping short of their destination. But this is another problem for the institution, how would it cope with a subpopulation of people who have decided that the price their ancestors were willing to pay for their descendants (that price being life imprisonment for all generations in between) is too high

I agree with your last point as well, there's not a lot of reason to pay the imprisonment price unless the alternative is far worse.

137:

@ 129:

I don't know how rare habitable planets are, or how expensive interstellar spaceships are.

I'm not sure what you mean by habitable planets, see an earlier discussion on this blog.

I'm not sure on this one either, but the canonical scenario seems to be that the generation ship takes up residence in the local asteroid belt and becomes the nucleus of a new space-based polity. "Habitable" planets don't just have a deep gravity well, they have a rather nasty atmosphere to contend with. Also, an oxygenated atmosphere implies some sort of local life, I would think. Gotta be real careful about contamination . . . both ways.

138:

Why generation ship has to have a stable social structure ? It's just enough that there is not certain social stuctures. So they have a dictatorship every 27 years and priest run goverment every 12 years or so.. And so on... Just make sure there is not a suicide cult ( that will effectively end the mission, others not so)

139:

That's a form of dynamic stability instead of static stability. Party-based representative democracy is itself an attempt at dynamic stability.

(Quite how you get both the dictators and the theocrats to relinquish power is another question, unless you have a distinctly unusual constitution and one that both will actually follow.)

140:

Right...so you have your dictator. What are you going to do when the oppressed masses rise up and throw his ass out of an airlock? In the process fighting and violence kill a healthy proportion of the crew and damage a lot of the ship. The missions a fail because theres not enough crew to repair the ship.

As for your priest idea, well that implies that you are going to get all of the crew to be the same religion. And not just the same religion but the exact same religion, no splits or anything. What happens if the navigators question the faith? Are those heretics marched out of an airlock as well?

141:

No, no, no! It's not a generation ship, it's a *home*. People live there. They expect to continue living there. Planets are places that are uncomfortable, rude, and primitive. "*We* don't live like that anymore."

I'm not proposing immortality, or even lives of thousands of years. 150 or so would be enough. And there is no "destination".

In the scenario I'm proposing these were people who lived on a space habitat in Sol-space, but got into a political or religious disagreement with the current government, so they left. They were pre-adapted because their habitat had already specialized in mining cometary heads etc. out beyond Pluto.

Effectively it's a generation ship, because when they get to a large body of matter with enough different resources, they build a separate habitat and split the "colony" in half. Think of it as a colony organism, but with people rather than slime molds.

But you *do* want extended lifetimes to improve political stability. People (esp. males) in their late teens and twenties tend to be the political dissidents. By extending the lifetimes and rigid population control you effectively limit their influence on the political structure by diluting them. (Yes, of course they will congregate anyway. But consider today's political climate compared with that of the 1960's and 70's, when the bulge of the population was much younger.)

P.S.: It's not out of reason that if they happen to end up at a good planet to colonize, they might do so. But that sure won't be where their intentions are focused. And that would probably only be considered after the population had started swelling in preparation for the split into the new habitat that they were already in the process of building.

However, I consider it extremely unlikely that any uninhabited planet will be suitable to support earth life without extensive terraforming. So they just won't bother.

P.P.S.: This is my development of ideas largely created by George Zebrowski and published as "MacroLife". I think he postulated unreasonably high speeds. (OTOH, some of the roots lie in Olaf Stapledon's "StarMaker".) But don't blame either of them for how I've developed the ideas, or when I've taken seriously what they intended as a plot device.

142:

You imply that religious homogenity is one of the hallmarks of faith, again, that may not have been the norm, with monotheistic faith as possibly just being an extreme.

143:

It occurs to me that the crew who are alive at the end of the trip may not want to colonise a planet. Especially if they have to terraform it. Add that to the wealth of experience they will now have in building sustainable habitats (in both the technological and social sense) its far more likely that they would just stripmine any planets or asteroids and turn the new system into a hive of habitats

144:

I wasnt implying any such thing. I was implying that a variety of faiths on a theocracy led generation ship is a recipe for disaster.

145:

> If you took the entire population of the world over the whole of human history, I suspect you'd find that the vast majority of them were living under the same system of government as their grandparents

Uh, no? The current governments of the two most populous nations, China and India, only date back to the 1940's. Of the top 10, which between them claim 4 billion people, only 2 countries (USA and Brazil, 500 million total population) have governments dating back to before WW2.

146:

Ah, sorry, missed the "over the whole of human history" bit. But that's not really fair, since for most of human history, civilization had basically one form of government: monarchical despotism, with few variations on that theme. And under those conditions, it's not an exaggeration to say that a change of leader can be called a change in government.

147:

I'm amazed because everybody seems to imply a repressive regime has to be either a dictatorship or a theocracy, when even quite egalitarian societies can be nasty to outsiders. Lynch mob, anyone?

Problem is, first of, IMHO HSS is a social animal; we want to apply to our peers. There is one piece by G. K. Chesterton where he mentions that historically, most dissenters'd have taken offence to being labelled heretics, they were the orthodox, the others were the heretics, and is surprised that today 'heretic' has come to be something of a sign of quality. YMMD, but having some rural or traditional relatives makes one agree somewhat.

There are a plethora of ways a majority can press there way on a minority, one of them being ostracism or 'shunning', as our fundamentalistic Christian brethen call it; there is one text about a Hopi experiencing said premodern mobbing, and the result was not pretty, but effective. In a way, this micht mean we wouldn't have to find ways to keep the minority in check, but we'd have to find ways to keep the majority from keeping the minority in check too much.

On a related note, it might be that the people who volunteer on such a mission are not the ones you want to have on such a mission, namely the colonists shouldn't score that high on the novelty-seeking scale. That's already a problem in contemporary space flight, see 'test pilots' vs. 'agreeable crew men', but well, some psychological testing, the right social drugs and some way for sublimation could do.

P.S. If I transgressed some guidelines with a more sarcatic note, could our gracious host please let me know?

148:

You could spin up the structure, then add the water (and other contents)...

149:

Well, it may, and it may not. If you look at the examples, there is also the interpretatio graeca and it's Roman successor, and the Roman empire had some theocratic qualities. E.g. the Roman emperors held the title of pontifex maximus till one of them flipped to the pale nazerenes...

http://en.wikipedia.org/wiki/Pontifex_Maximus

It more depends that most of the different faithes play along; given the Roman example, the notorious exeption were the Xians, refusing sacrifice. And later talibanising the whole thing after Constantine...

150:

One point you're ignoring is the size of the "prison".

Given that 80% of US citizens don't hold passports -- essential for travel outside the USA -- one would assume that 80% of Americans consider the USA to be room enough to live their lives without feeling constrained. That's 300M people in an area of just under 10M km^2, much of it wilderness.

Consider a big generation ship; it's 100Km long, has 100 inhabited cylindrical decks (concentric cylinders), each deck has a surface area of approximately 0.1M Km^2, so it's roughly 300Km in diameter. (This is back-of-an-envelope territory.) This ship has around the same land area as the USA.

It's probably a lot bigger than we need; remember, much of the USA is wilderness, and the overall population density is 30/km^2. In a city like Manhattan the population density is on the order of 30,000/km^2. If we assume our colonists will accept Manhattan levels of density (which is not as dense as it gets; Cairo's densest district in 1994 was around 109,000/km^2, while the walled city in Kowloon -- demolished, and a slum -- was close to 200,000/km^2), then our US population requires 10,000km^2 of land area. Triple it -- to provide for intensive agricultural systems and a wilderness area for vacationing -- and round up to 100,000 km^2, and go for a ship with 50 decks, and you've got 2000 km^2 per deck. Cylindrical, that approximates to 30km diameter by 20km in length.

(This is an attempt at hand-waving a self-propelled nation with a huge, teeming population and enough geographical diversity to give city-dwelling folks the illusion of wilderness to explore.)

151:

I was thinking more along the lines of the original cyber prefix that about the bastard son on uninspired Dickens fanboy/girlship and Carnot's principle, but then, being born into a society that has all the positive and negative aspects of a 18th century mountain community with the scientific and cultural knowledge of the post-21st should be for strange values of fun...

152:

I like living in a city, but the Earth *is* overcrowded. We are rapidly using up non-renewable resources. (More accurately, we are increasing the cost of retrieving them, but without enough energy to extract them from sea-water it's about the same.)

That we are doing so isn't new. Every civilization in Earth's history has done so. And they've all died. Sometimes directly because of resource depletion.

When we are wiping out species to keep ourselves fed, then either the Earth is overcrowded with humans, or we are insane ecological terrorists. Or, of course, both.

I think the proper population for earth is probably around what it was in 1700. This is probably enough to sustain and improve a highly technical civilization without rapidly degrading the environment to such a point that the civilization collapses. As we seem directly headed for. (Just in passing, I'll note that people of 1700 also wiped out species for their convenience. But they did this in a kind of innocence that we no longer have. They tended to believe that species *couldn't* be wiped out, despite the evidence in front of their eyes. This "innocence" is not a good thing. It's a close cousin to idiocy. But it does mean that it's unreasonable to accuse them of evil. [Unlike modern whalers, or tuna fishers.])

And, yes, most people would still choose to live within easy commute distance of their job. (The split between work and home is one of the main reasons many people prefer to live in the city.) I like the idea of Archologies. But I've never seen anything approaching one that I'd like to live in. (OTOH, I've seen a few that I wouldn't mind living in, if they didn't cost extra. But they tend to be *very* pricey.)

153:

Your comments:
The poem is applicable to a single individual (usually male). It's rarely applicable to a family. (US history includes a few examples.) For a sizable group of people??? I can't think of one example in history. And only a few in myth or legend.

In history the reasons sizable groups of people move is either:
1) massive force. Example: forcible relocation of the Jewish people to Babylon, etc.
2) religious arguments. Example: the Mayflower. These people left because they wanted to and could afford to. (It was expensive!) But it wasn't entirely a free choice.
3) hope for better living conditions: Example: Families moving along the Oregon trail. Conditions needed to be pretty bad at the starting end, but people still needed to be wealthy enough to afford the cost of the Conestoga & supplies.

Counterexample, sort of:
Polynesian sailing families would sometimes explore. Many of the island cultures were founded that way. We don't know how often this was intentional, and how often they just took what advantages could be taken of surviving a storm at sea. (IOW, this could be a from of "massive force")
N.B.: The folk-epics will never put this down to a mistake, or happenstance, but that doesn't mean they should be believed. And sometimes even the folk-epics will say that they were fleeing invaders. (Cf. Virgil's The Aeneid.)

154:

True true, i'll give you that. Though the prison thing could also apply in the sense of isolation. Travelling at 0.01C they would still get a lot of communication from Earth. We've have all ready postulated a system wide civilisation with enough energy and labour to launch at least one generation ship, it stands to reason that they are making quite a lot of advances. Confined to one generation ship they have very limited resources, bit like leaving a really cool party and getting texts on all the fun whilst you trek home in the cold

155:

Confined to one generation ship they have very limited resources, bit like leaving a really cool party and getting texts on all the fun whilst you trek home in the cold

I seem to recall an SF novel of a few years ago that made exactly this point, as a possible solution to the Fermi paradox. Ah, what was it called? Accel ... Accelerator ... Accelerant ... something like that ...

156:

Not really. They're not only outliers, but they are also only fragments of a society. Small fragments. Highly dependent upon the rest of the society with which they integrate. And even so....

When I look at records of Oxford from the 1800's and look at recent records, they don't seem to be about the same organization. The name's the same, and some of the locations are the same, but that's about all. O, yes, and they're both schools.

Having the same name doesn't make it the same institution.

OTOH, I also agree that through most of history most people lived very stable lives (in that each decade was like one of the decades their parents lived through). Technological change is very disruptive of that.

In fact, as I consider further this discussion, I consider it less likely. We are talking about things that won't happen for over 50 years, and at the CURRENT rate of change, that means we can't predict what the culture and technologies available will be. We know what we can predict, but the history of the last two centuries tells us that this doesn't give us much likelihood of not missing what the folk of that time will think of as crucial pieces. (Some of this is intentional, of course. Charlie is looking for things that will be a good story. Too high a tech leads to magic-wands.)

E.g.: One thing that exists in prototype today is the three-dimensional printer. Mostly they just print plastic, but a few can also lay down electrical traces. So far they are mainly used for proto-types. This won't always be the case. I'd guess that in five years they'll be used for custom machining that doesn't require much strength, and in 10 years they'll be able to give tensile strength (by embedding, say, carbon fibers. Perhaps compressive strength is another 5 years, and torsion-resistance yet another 5 years. That gets us up to 2037 when 3-d printers are able to replace most things that require lathes and machine shops today. This makes carrying spares much less of a problem. And one thing they'll almost certainly be able to do is build the parts required to make another 3-D printer, only slightly larger. (Or, of course, smaller. But larger is the problem. It may only be able to scale up 10% or 20% per generation.) And this isn't a magic wand. This is a linear development of something that already exists.

But energy *is* a real problem.
Which caused me to wonder:
If you have a SpaceHabitat in Sol-space, but not in orbit, what is the size of solar sail that would be required to support it, assuming that it was also used to run a Stirling Engine to supply electricity to the Habitat? (This means that we are assuming the photons are captured and then emitted in random directions rather than being reflected.)
Naturally this will be different for different distances from the sun, but make the estimate for several different distances. (Would they be different? Gravity falls off as the square, but so does insolation.)
I feel the answer should be a simple proportion to the mass of the station, but to keep things simple say a mass of 10^9 Kg.
And how far out could we get enough electricity out of it to run the station? (I'm totally out of my depth here. Some of these I could try to calculate, some guesstimate, but here I've got no idea. I know neither efficiency nor requirements, and can't even make reasonable guesstimates.)

157:

That`s considerably more swanky than anything I`d imagined. If we can pull those off they`d do nicely as permanent in-system habitats.

Anyway, I`ve been mulling the whole claim jumpers scenario a bit more and it`s actually rather likely, in that the motivation to send a colony ship in the first place would be the detection of a really tempting piece of real estate, say an earthlike planet that had unmistakeable biosphere markers (Oxygen, methane? Whatever)

Say we send the colony ship using fission propulsion, then 50 years later fusion really is discovered for real (Or some other game changing tech), are we going to wait an extra 200 years to place humanity in another solar system out of politeness to those nice folk in transit? Especially given the cost of the mission has now fallen by a couple orders of magnitude and we have telemetry and data from a working example experiment 50 years old.

That said, a whole new planet can probably accommodate several colony ships worth, so it wouldn`t be that hard to give the slowboat folks some assurances that they`d get living space, more than they`re used to.

Though as I said, I was thinking of something rather smaller than "The US in space".

158:

Can't have been that good, if you can't even remember its title.

159:

Memory problems as well as eye sight eh? You want to take a rest charlie!

160:

Just a point: modern whalers aren't anywhere near extinguishing any of the whale populations, and don't particularly want to. Bluefin tuna is another matter but green organisations haven't put much protest effort into fighting the serious overfishing of that particular species, preferring at the moment to continue to concentrate on the ceteceans which are not at risk of extinction due to human predation.

The cod and many other fish species are also on the edge of extinction due to overfishing but they're not cute and cuddly like orca.

161:

Two thoughts:

1) Re the ol' claim jumpers thread - if you are the faster, higher tech, follower who's looking to jump ahead and claim this nice new territory, and you know where the first leavers are (as you will) - then you would be smartest to send a small, fast missile down the path taken by your competitors. At the relative velocity difference between 0.1%c and 0.01%c you'll still remove the problem before it gets there.

2) One good reason for doing any of this is to escape some threat, probably political, behind you. However in that respect its no good just hopping to a nearby star system - before long you'll have threatening visitors turning up from what you were trying to escape (they are at the same tech level, remember?). Nope, you sit in a generation ship and you travel onward as far and as fast as you can - until the ship starts breaking down and you have to stop. Cue novel - "Escape from the Space Nazis".

162:

@161
1) That's a very good reason for the early leavers to _not_ send back any information whatsoever. And to sneak something on board to alter their trajectory even a tiny bit once they are far enough away that the new trajectory would be too difficult to track.
2) If the threat one is escaping is a collapsing civilization, being followed may not be an issue.
Cue "But what if the 'Space Nazis" show up and turn out to be totally different from what was fled. They are all warm and fuzzy. Or they seem like it at first. But are they really?

163:

O'Neill made a similar calc for space colonies. He assumed that the mirror mass was no more than 2x the habitat mass of the colony and no more than 10 light wavelengths thick. That allowed a colony to be placed 3.7 light days out, 10x Pluto's average orbital distance.

164:

If the ship has a land area of the US (probably in safe, Disneyland style) what exactly is the reason to colonize another planet? Aren't we back to O'Neill's point (and Dyson's), that lebensraum is more easily built, with a lot more potential space, than trying to go somewhere else?

And if the Mayflower was a modern luxury cruise ship, one suspects that the colonists would have had to be pried off the railings on arrival.

165:

@ 150:

Consider a big generation ship; it's 100Km long, has 100 inhabited cylindrical decks (concentric cylinders), each deck has a surface area of approximately 0.1M Km^2, so it's roughly 300Km in diameter. (This is back-of-an-envelope territory.) This ship has around the same land area as the USA.

Wow! This wasn't what I was thinking of at all - as someone else said, Swanky! Maybe you should - without giving away any spoiler details of course - give us a few more specifics about this ship of yours.

Me, I was going with a cylindrical hab approximately 50 km long by 20 km in diameter because those are the classic Rama proportions. But that isn't where we really diverge; 100x300 isn't much more than an order of magnitude in difference (actually, a factor of 30), iow, completely negligible ;-)

Where we differ - and I think this assumption is critically important - is the number of decks in place. I was simply assuming you scoop up a big enough piece of the Earth so that with a little hand-waving you can tolerably expect it to perform as a closed ecosystem for maybe 1,000 years, and then you roll it up and cap the ends. Nothing fancy, total area on the order of 3,000 km^2. And while it's big, it's not that big; I could walk the length it in just one day (I'm a really fit, type A, skinny sort of guy :-)

Your boat, otoh, has swelled from maybe one order of magnitude larger than mine to something over 3,000 times the size!

I suspect that this is one of those quantitative changes in parameters that is so large that it becomes a qualitative change.[1] Any other characteristics that make your ship something other than an O'Neill on wheels, er, rockets? It sounds like you can afford not just a really big boat, but an entire fleet of outliers, including a small flotilla of little guys not much more than 2 km in diameter by maybe 5 km long.


[1]Shielding becomes much easier for one thing, as does provisioning.

166:

I too was thinking smaller than Charlie's vision - an O'Neil Island Two/Three (holds the minimum population size in earth like comfort) or a very large building with ag/park areas with a similar size population with very high density living.

IMO, the bigger and more luxurious the ship, the less desire to leave at planet fall. You would almost want the ship to be unpleasant at the trip's end. Planned obsolescence over 1000 years!

167:

"In the terms of my earlier discussion of interstellar colonization, I classify all these technologies as "magic wands": FTL propulsion, mind uploading, true general AI. Any one of them radically alters the picture for interstellar colonization".

I have to question if the only viable (interesting?) alternative in the light of lack of these sorts of technologies is the generation ship.

As these various threads have explored, a hard part of the problem is keeping current humans continuously and consciously alive for generations. No cold sleep allowed. But do we need to? We can certainly encode DNA for millions of species and store it as information. We can create synthetic life, or at least quite nearly, so we cannot be that far from creating new life, and incubating it when needed.

Similarly, we are progressing with matter printers, so again, we have a machine approach to replication that allows us to build with local resources on arrival.

Using this technology, we could at the very least, send out very fast, small ships out to the targets and prepare them for occupation, even as small habitats/colonies, rather than full planetary terraforming.

But supposing we did send the information to construct millions of humans and rear them on site. We only need to do this for a genetically small population. Education by machine could be quite simple, and bootstrap over 10 generations or more to get to at least early C20th level. The hard part is getting the first few generations to survive and supplant the machines at keeping them alive with food. If that was possible, then a ship that used this approach could potentially outstrip the capability of a generation ship at delivering a relatively advanced civilization at a target for a time period t.

While it appears that there is much hand waving, the staged education of children might be a lot simpler than the vision of robot nannies. Children could be reward trained to come to the education facilities and given some form of education (language, food gathering). Each generation could learn something new and leverage off the previous generations. 10 generations might be enough to get a "normal" society working again, able to develop by using the matter printers to create tools.

Even if we could only create simple agricultural city civilizations with post stone age technology using this approach, we could seed the galaxy with such civilizations and await the results of our sowing. Unlike generation ships, we could seed the galaxy as fast as our technology would allow, perhaps at 0.1c or better, with a cost substantially below that of generation ships.

I don't think the technologies involved are classifiable as "magic", certainly not within the time frame that would allow large generation ships with suitable propulsion and life support to be built.

168:

"await the results of our sowing"

Interstellar missiles aimed at us for the crimes against humanity committed against their ancestors?

169:

Who knows what the future holds? :)

170:

I think part of why he was thinking so large was due to that thought experiment a few months ago where he worked out that the size needed to have a independent, stable ecosystem in the biological, social, and technological sense was way larger than generally speculated- US/Europe size was, if I remember correctly, about right due to the immense complexity of modern human society/only moderately understood human biology.

171:

Yes, I know. It seemed to morph from the low 6 figures upward. The problem is that as society gets ever more complex, the minimum size increases. Even O'Neill 3's aren't large enough to support 10's of millions of people. Heinlein had it so much easier when he assumed that colonists would be farmers with barely C19th technology. With that technology level, genetic diversity is likely the constraining factor to minimum population size.

In the post O'Neill era, one really needs a new rationale for interstellar colony ships that solar system space colonies doesn't solve. That seems to be mostly missing in these discussions. Perhaps it is a case that the solar system will fill up, then when resources finally get short, the generation ships start to leave. That could be some time.

If the Asimovian universes didn't have hyperspace flight, then one could see the robots perhaps wanting to get away in slow ships which would be very hard for humans to emulate.

172:

The idea that the robots would flee the humans ("they're so slow, and booooooring! oh, how very boring. Do you know, they can't even understand hyperdimensional chess?") in very slow spaceships is marvellous...

173:

No need to wait, we're already living in the future - production 3-D printers already work with titanium at decent resolution and up to 100% density. They're used for printing artificial hips with much better forms than could be made with traditional methods.

Laser Sintering (LS, a.k.a. "Selective Laser Sintering"(SLS), "Laser Fusing", "Selective Laser Melting (SLM)" and "Direct Metal Laser Sintering" (DMLS)) has good resolution (20-40 micron layers, 100-200 micron spot, 25 micron accuracy) works with titanium alloy (6-4), bronze, Inconel 625 and 718, cobalt-chrome-molybdenum, maraging steel, stainless steel, aluminum alloy (Si10Mg), and - usually on a separate machine - various thermoplastics with or without glass, carbon or aluminum fill, wax, elastomeric thermoplastic, or potentially nearly any powder that melts in a laser beam. You can make a large subset of anything with those materials - ~ 95%+ of a jet engine, for instance.

Electron beam melting (EBM) has about the same capabilities in metals, but with better part properties and due to the vacuum and faster beam slew due to the field-based optics.

The parts are still expensive compared to mass-produced ones (upper bound: a small finished metal part, qty. 1, is roughly on the order of $40/cc of the enclosing box / lower bound: powders start at about $175/kg., ~$50+/hr. for equipment). Parts are generally small (under ~30 cm) and single-material, and usually require post-processing for finish and heat treatment.

174:

What do think that would mass? I figure 1-10 tonnes per m^2, 333 m^2/person, 300M people = 1E14 to 1E15 kg.

At $10,000/m^2 it would cost about a quadrillion dollars, not counting propulsion, but that could be off by orders of magnitude either way, depending on technology.

Also, looking at high-yield gardens 200 kg/m^2/yr of a balanced mix of vegetables is possible. That's nearly enough for one person. Certainly 5 m^2/person would be ample.

175:

Whoops, those were 18" by 30' beds, not 18" by 30". I thought that seemed a little off. Multiply the area required by 12 and carry on.

176:

"American foundation myths are an aberration: most people have been born, worked, married, had kids, and died within ten miles of the same spot."

-- actually, in many cases that's not so.

According to the demographic research I've read, as far back as the 1600's only about a quarter to a third of English people died in the parish in which they were born.

And already by then, 10% of each generation were leaving for London. Not to mention hundreds of thousands leaving for Ireland and the Caribbean and North America.

Judging by the Amesbury Archer and his kids, long-range movement wasn't anything new in the Bronze Age, either.

Although it offends recent archaeological orthodoxy, it's becoming increasingly clear from things like DNA studies and analysis of tooth enamel and bones that both individual and mass migrations are historically as common as dirt.

177:

OTOH wheat is desperately inefficient per acre. Figuring 3x the UK yield for greenhouse conditions, it's still only 2.4 kg/m^2/yr = ~8000 kcal/m^2/yr.

178:

Also, you don't have to know -everything- to do -anything-.

You can just blunder ahead, do the best quick-and-dirty preparation possible within time and money constraints, and accept that shit will happen.

Learn from the mistakes, wave goodbye to the dead, and try again until you succeed.

That's essentially how Europeans colonized the New World; massive ignorance and trying over and over again until something worked, making notes along the way.

"Croatan"... 8-).

You learned by doing and gradually built up the needed toobox; you didn't try to anticipate everything in advance because it was impossible to do that and anyway it would take too long.

Half a million or so people from England migrated to the New World in the 17th century, for example.

Well over half of them met various gruesome forms of death quite soon after they landed, and that's not counting the very substantial number who died on the way.

The number of English colonists living from New England to Barbados by 1700 was roughly 250,000, which was around half total number of emigrants to that date.

And that quarter million included all the natural increase of everyone who'd stepped ashore since 1607. It was a few lucky lottery winners and their descendants.

Emigration was extremely risky; everyone but the very gullible knew it.

Moving to London, a disease sink nearly as deadly as Virginia or Jamaica in that period, was a gamble too, but ten percent of every generation took it.

179:

I would assume that by the time we're up to building a generation starship, producing food by anything resembling conventional (as of now) agriculture will be sort of a quaint hobby for antiquarians.

Direct nanoscale assembly of the necessary molecules, or some sort of genetic manipulation to vat-produce the food would be used instead in closed environments.

We're really in the position of Verne writing FROM THE EARTH TO THE MOON (worse actually) if we try to imagine how interstellar travel will be done 200 or 300 years from now.

He tried to do "hard" science fiction and had his explorers use a giant cannon to shoot themselves to Luna.

It would probably have been smarter, and no less realistic, to think up some dilithium crystal style bafflegab (Cavorite, anyone?) and then just get on with it.

We can't imagine what technology will be used centuries from now; if we could, we'd patent it, not waste our time writing stories about it.

180:

"And if the Mayflower was a modern luxury cruise ship, one suspects that the colonists would have had to be pried off the railings on arrival."

True enough. Most people don't realize that the Mayflower passengers were mostly servants sent ahead to prepare the way for the toffs coming on later ships such as the Anne. They also thought they were going to Virginia, but the Mayflower's captain had other ideas. The relief ship, the Fortune, carried no useful supplies, only 21 adventurers in search of treasure. There's a story in there worth filing off the serial numbers and moving across state lines.

181:

If you are looking for a possible near term viable fusion drive try Plasma Focus Fusion using a Hydrogen- Boron (aneutronic) fuel. This setup is a already virtually a rocket configuration:
http://focusfusion.org/
http://en.wikipedia.org/wiki/Dense_plasma_focus

182:

True enough. Most people don't realize that the Mayflower passengers were mostly servants

-- a minority of the 102 settlers, in fact.

52 were members of the Leiden Congregation and their families; that is, the Pilgrims proper, of whom 13 were family servants.

31 were "Planters" and their families recruited by the London merchants who were financial backers of the enterprise; independent immigrants, with 5 family servants.

The remainder were "servants" proper, under (short) contracts of indenture. Several of them, however, were relatives of the Pilgrims, probably poor relations.

>sent ahead to prepare the way for the toffs coming on later ships such as the Anne.

-- there were no toffs in the Leiden Separatist community, I'm afraid. A solidly lower-middle-class group.

>They also thought they were going to Virginia

-- to be precise, some of them thought they were going to the Hudson Valley, which was on the northern fringe of the Virginia grant as of that date, but of course also claimed by other European powers and companies.

The Leiden Congregation group just wanted some place where they could start farming, preferably a rather isolated one.

183:

"Moving to London, a disease sink nearly as deadly as Virginia or Jamaica in that period, was a gamble too, but ten percent of every generation took it."

What are your thoughts on the reasons for interstellar emigration? Is there an economic driver as there was for those moving to London or the Colonies?

184:

There's always the richard k morgan approach of digitized human consciousness and fast-grown clones. With the right technological advancements, you don't need to ship a biosphere across interstellar distances, you just need to ship a shit-load of machinery. Hell, even a few extreme advances in cold sleep would work.

Every approach here seems to be bottlenecked by the need to sustain a biosphere and a society during the journey.

185:

Actually, the first novel I wrote last year was predicated on an interstellar colony where you don't even get fast-grown clones. If humans are uploaded, a lot of time constraints disappear.

Thing is, in this scenario, making a biosphere complex enough to maintain a population of humans is effectively a display of conspicuous consumption and technological capacity, not a necessity. Politically, a human colony might be a great status symbol, like, say, a space program or a nuclear reactor. It does make for interesting stories, but then again, humans do make great pets.

186:

Every approach here seems to be bottlenecked by the need to sustain a biosphere and a society during the journey.

That's true about Spaceship Earth too. But I don't think of the biosphere as a bottleneck. It's a feature. And I don't think "fire the customers" is quite the right marketing strategy for our spaceship going forward.

187:

@ 140
"Good Eating" - I forget who wrote the story, now.

@ 142
H. Beam Piper, of course, famously disagreed, as evinced by "Lord Kalvan"s speech in the novel.

@ 143 et seq ref: Gneration-ship vs. FTL (and bombing the slowboaters) and settlement vs "the Ship's our HOME!" .. and apart from WHY would anyone want to bomb the slowboaters, there is a little-known novel on this, called: "Mayflies" by one Kevin MacDonnel (jnr) ... worth a read.

@ 152
NO
A stable Earth poulation with decent modern recycling and energy-conversion (as we are approaching) could ealily be as high as 5 billion. Though 1 - 2 billion might be better.

@ 153
Re your comments on the Kipling excerpt... maybe.
But, that exploration has to be done by somebody, even using remote probes. And, at least one of the epics has the "hero" going exploring because he isn't wanted around, because he's killed people - Greenland/Vinland.

R. Sneddon @ 160
Fishing.
Cod are NOT "in danger of extinction" - worldwide, and sustainable fishing schemes are catching on (pun intended) The problem lies with thiose greedy bastards who won't co-operate with the sustainable quota schemes. Very much like the logging problem in tropical forests, in fact, where, in my opinion, the danger is much greater. (Tress and plants can't move around.)

164 & 165
It's called a terraformed asteroid, hollowed, spun up, fitted with motors, etc. And see my comment above about - "but the ship's our HOME!"

@ 170 / 171
Minimum population for diversity/ tech knowledge.
Sorry you need less than a million people PROVIDED you carefully select the input, so that all your tech bases are covered, and your education systems are well set-up.
Remember, people can and do multi-task.

@ 173
How long before this hi-res metal-shaping rep-rap printing tech becomes common, and at what price?
I'm assuming these are prototypes in 1's & 2's at present.

AND ... I'm obviusly going to have to re-read "Accelerando" again (again) as it's obvious I've missed several nasty points. Oops.

188:

Well, my point is this: if you postulate a cylinder hab, then what are you doing with the space between your head and the axis of rotation? Gerard K. O'Neill's colony cylinders had longitudinal windows and reflectors outside to direct sunlight into them, but they were in solar orbit; that's not going to do any good for a generation ship (leaving aside issues of thermal expansion/contraction which apparently make them murderously hard to maintain). Generation ships don't need windows. So ...

Volume is not entirely mass-free; there's some structural weight associated with it. So why not put a slightly smaller cylinder up there? Plate it in LEDs to give daylight-spectrum light and paint clouds or something else that's pretty to look at; it's far enough away that it isn't going to induce claustrophobia. Yes, there'll be an odd bowl-shaped horizon cut-off, but again: you've got control of the lighting system, you can play games with it to avoid the visual effect of a huge rolling cylinder hanging overhead waiting to mash you flat.

Once you decide to build this way, you can have an order of magnitude more habitable surface area.

As for why to build so big? Well, see earlier discussions about the minimum size of society necessary to maintain a technological civilization. My guess is that you can't maintain a starship unless you've got nearly enough specialities to build one in the first place. A population the size of today's USA is probably not necessary, but I think we can safely say that a society that big could in principle build and maintain infrastructure on an epic scale and conduct interplanetary or interstellar exploration. Especially if it's diverting the level of energy into those tasks that the USA currently directs into its military. It may be overkill, but I'm pretty sure a mission on that scale would be up to the task of colonizing a new star system, if not terraforming terrestrial but non-biosphere-infested planets.

If you're going to spend the money to send a generation ship in the first place, there's no point in not sending the very best.

189:

But supposing we did send the information to construct millions of humans and rear them on site. We only need to do this for a genetically small population. Education by machine could be quite simple, and bootstrap over 10 generations or more to get to at least early C20th level. The hard part is getting the first few generations to survive and supplant the machines at keeping them alive with food.

Er, no.

DNA isn't enough to encode a viable organism -- but you can always ship frozen fertilized ova. Building a mechanical uterus is a very difficult job, but not obviously impossible. So it may be possible to manufacture canned babies on site.

The real problem is that you're dead wrong about education by machine being "quite simple". Most of what makes us human is acquired/transmitted cultural traits which are transferred horizontally from other humans; raise a human baby in social isolation (providing nutrition and shelter but no contact with other humans) and you don't get a human being, you get a speechless and badly emotionally damaged naked ape.

It seems to me that the problem of raising properly socialized humans is actually an AI-complete one -- any machine system capable of educating and socializing an infant has just passed a rather sophisticated Turing test: it's demonstrated that it is capable of operating as a fully socialized adult participant in human society (a "parent"). So the "let's just send fertilized ova and raise them on site" colonization plan still relies on a magic wand technology.

Now, you also mentioned cold sleep. That's an interesting topic. Are you familiar with recent work on suspended animation? On its own it's not enough, but if we also develop better medical techniques for treating cancer, and life prolongation (both of which appear to be interdependent and are currently the focus of quite a lot of research), then we might be going somewhere. Literally. (The cancer treatments are going to be necessary because of cumulative cosmic radiation damage over exposure times measured in decades or centuries; longevity treatments ditto because even reducing metabolic rate by an order of magnitude won't stop the ageing process completely. But a combination of these things might allow people to embark on missions with century-plus durations.)

190:

"A population the size of today's USA could in principle build and maintain infrastructure on an epic scale and conduct interplanetary or interstellar exploration."

Imagine what a society that size could do if everyone received all the education they were capable of handling and then were given the opportunity to actually use that knowledge.
Also, how fast would science and technology develop compared to now?
I have no idea, but I would love to find out.

191:

They'd probably all starve and drown in their own waste. Having a whole country of people employed in R&D implies that they import their industrial and service industries.

192:

You can just blunder ahead, do the best quick-and-dirty preparation possible within time and money constraints, and accept that shit will happen.

Learn from the mistakes, wave goodbye to the dead, and try again until you succeed.

I don't think that's practical in terms of space colonization. There's no "there" there -- nothing to breathe, nothing to eat, an environment that will kill you dead in seconds if your isolation procedures fail.

North American colonization was fault tolerant for humans insofar as it had breathable air, drinkable water, there was game that could be hunted and locally available food: it was a human-life-supporting environment.

Going into space is a bit closer to trying to colonize the central Arabian Desert in high summer, if the Desert was first flooded with nerve gas, and if all your supply requisitions had a five year turn-around. (Nerve gas: you can't breathe the air. Arabian Desert in summer: you need climate conditioning or you fry or freeze. Resources: you have plenty of silicon, and you are a drill string away from hydrocarbons and water.)

An immediately-lethal environment is manageable if the supply chain is short -- that's why we have oil rigs in the North Sea or a large research station at the South Pole. And a slowly-lethal environment is manageable with a long supply chain, as witness the North American colonies. It's the combination of the immediately-lethal environment and the long supply chain that's the killer problem here.

193:

Terms of debate: I'm ignoring magic wands (stuff we can't do now and may never be able to do). Specified magic wands so far include: true human-equivalent AI, faster-than-light or other magic space drives, cheap'n'easy fusion, safe and reliable suspended animation, and finally, magic fluffy nanites.

That we'll be able to manufacture molecular-scale components pretty soon is not in question -- but the first generation tech for doing that is emerging from synthetic biology. The sort of things Eric Drexler was writing about in "Engines of Creation" or "Unbounding the Future" is ... optimistic. For values of "optimistic" that may turn out to be equivalent to "energy too cheap to meter" once we have fifty years of hindsight. On the upside: in that case, we don't have to worry about grey goo. On the down side: no magic wands.

I think it's more interesting to examine how far we can get without presupposing the development of "magic wands" that make everything easy. Hence this discussion (and previous ones).

194:

Dude, who do you think you're lecturing here?

(Hint: I'm going to assume you've read some of my novels. If not, start with "Accelerando", then come back to this discussion as a critique of the ideas in it.)

195:

Confined to one generation ship they have very limited resources, bit like leaving a really cool party and getting texts on all the fun whilst you trek home in the cold

Depends where you're starting from and comparing yourself to. "Stuck in a terraformed cylinder 100 km long" may be a bit restrictive if your alternative is "living the good life in California's beautiful San Fernando Valley" but it might be a bit more appealling if the alternative is "dying in a refugee camp on the Thai-Burmese border".

196:

#various on O'Neill / Dyson habs.

None of you thought of (or read) Colin Kapp's "CageWorld" series? In which the Sol system is converted into a series of concentric Dyson spheres, with the planets retained like bearings in a ball race (hence the CageWorld name)?

197:

I read this and thought "that's not true, I got an email from Greenpeace only yesterday about tuna fishing!" But then I went and re-read it, and it was mostly about sharks, turtles and possibly dolphins in the bycatch.

Their campaign website on tuna focuses on the tuna population itself, though.

198:

Indeed - choosing a certain level of life for you and the several generations of your descendants is a no brainer if it's guaranteed better than your current one.

199:

Kapp was a relatively obscure writer, mind, and I for one have not encountered his CageWorld series. I suspect it's been out of print for quite a while now.

(Having said which, the central idea in Kapp's Patterns of Chaos - a guy with the most justified paranoia ever due to being personally targeted by missiles launched 700 million years before he was born - is memorable.)

200:

Very true, very true indeed. But a generation ship on the order that the host has described (100+ km long with 100 decks) capable of surviving a trip of a few thousand years with no back up and then establish a civilisation on the other end is a massive investment of resources. Along the lines of requiring an entire economic block of super powers (think EU/China/US + far better technology) to build and launch. The people on it are unlikely to be refugee escapees. If the solar system falls into a huge internecine war* then escape via generation ship is a non-starter unless you already happen to live in one in all but name (a hab that is already self sufficient for example).

Either way one self sufficient Gship will only have what resources it takes with it. It won't be able to match the potential industrial and R&D resources back in the sol-system so will very likely fall behind on technology.

*If this war is so bad that it looks like only a few humans living in nuclear bunkers miles under a crust might survive then you may as well push yourself out to the kuiper belt and hide til its over. then come back and pick up the pieces, far safer than heading out into the unknown for kiloyears

201:

Along the lines of requiring an entire economic block of super powers (think EU/China/US + far better technology) to build and launch.

No, you're missing the point: it is an economic superpower (at least, in today's terms).

The best model for how it might be launched is for a section of an increasingly successful cis-solar space-based civilization to decide that it makes sense to move out to somewhere where there's less resource competition. If it's an already-existing space-based society, existing largely independently of inputs from Earth, then it's most of the way there (barring the propulsion system which is a separate, containable project).

Think in terms of Japan during the isolationist years of the Tokugawa shogunate -- relatively rich, civilized, populous, and isolated -- discovering that it's actually mobile, and there's an uninhabited and unclaimed continent beckoning thataway.

202:

Oh yeah I didn't consider it to be a ship just built and sent off by another polity. I was just using that example to illustrate how unlikely one is to be built ad hoc and sent off to escape whatever was going on in the solar system.

Im having trouble with seeing why such a powerful and autonomous habitat would decide to push off into interstellar space. Without the sun they would have to rely on bringing fuel with them.

Back of the envelope time again for a 300x100km habitat with 50 concentric decks each 1km above the other.
That's roughly 2.4million km2 of land. If each deck and the hull are 100m thick that makes 240,000 cubic km (plus a little air) of mass. That's trillions of tonnes, to shift that anywhere would require super-cheap fusion or super-cheap antimatter.

But how much wattage will be needed to keep the lights on, the machines wiring and generally keep the primates alive and entertained? I doubt the energy needed isn't going to be less than tonnes of antimatter for a journey of centuries/millennia. Though without knowing the energy budget of such a ship its hard to say

203:

just to add to that IIRC the specific impulse of antimatter is 1,000,000. To boost to even 0.01c would mean one quater of the ship would have to be antimatter/matter fuel. And thats not even to slow down, definitely seeing a need to a magic wand or two for this to ever work.

204:

I suppose one solution is just massive, massive redundancy. Enough repair parts to rebuild anything twice. Several semi- or completely independent biospheres and colonist societies. Things like that.

205:

Get back to me when Sea Shepherd[0] and Greenpeace are sailing Zodiacs around tuna boats trying to disrupt their catches the way they do with the Japanese whaling fleet.

[0] BTW whoever thought that was a good name for an environmental group? Think about what shepherds actually do to their flocks sometime...

206:

I've got the whole CageWorld series, but at my Mum's place, so inaccessible until Easter. Still, I mainly mentioned it for the BDO, which I described adequately for our purposes.

207:

Shepherds cull their flocks, yes - but they keep the SHEEP going.
What's the garuanteed way for an animal species to survive at the moment?
To become "domesticated" in some form or another - food or pets are the two best ways of doing it, especially in the case of the most poular pets - they have other functions.
If we didn't have the furry monsters, for instance, we'd have mice-infestantion - and/or rats.

208:

"DNA isn't enough to encode a viable organism -- but you can always ship frozen fertilized ova."

I'm well aware that we need cells to run the DNA code. That is why I mentioned the synthetic biology (c.f. Venter's achievement last year). I see no fundamental reason why a machine cannot construct the cell and DNA to get started, although we have no idea how to do this non-biologically today. Or we go with fertilized eggs or some synthetic egg construct that is more spore like.

"The real problem is that you're dead wrong about education by machine being "quite simple". Most of what makes us human is acquired/transmitted cultural traits which are transferred horizontally from other humans; raise a human baby in social isolation (providing nutrition and shelter but no contact with other humans) and you don't get a human being, you get a speechless and badly emotionally damaged naked ape."

You are arguing "wolf child" as your model. I agree that this is not a viable model. However, our ship is not raising isolated babies, but whole creches of them. We know babies do socialize with each other, and deaf/dumb children do construct their own languages to communicate with each other without help. We also know that monkeys can be raised with synthetic surrogate mothers, and orphanages are full of kids without nurturing parents. That is why I stipulated a number of generations to bootstrap the education level. The first generation will be mainly educated to talk a particular language and do basic child rearing. Each generation is incrementally educated to a higher level. The hard part is generation 0. Fairly dumb machines have to get babies to stay alive and get very basic language skills. TV programs are shiny enough to attract sufficient attention for language skill development (Sesame Street). I see no reason why operant conditioning won't be sufficient to get babies to get food, be presented for cleaning and watch the programming. A key training is to get the adults to return their babies to the ship/creche areas for further schooling each day. Each generation uses its skills to raise the next generation a level higher. Incrementalism is the key to avoid the need for AI-complete machines and thus avoids the "magic wand".
But let me be clear. I am not claiming that this will result in a Western human social animal. The product may be somewhat different.

"Now, you also mentioned cold sleep. That's an interesting topic. Are you familiar with recent work on suspended animation? On its own it's not enough, but if we also develop better medical techniques for treating cancer, and life prolongation (both of which appear to be interdependent and are currently the focus of quite a lot of research), then we might be going somewhere."

I suspect human hibernation will require genetic engineering to induce this state, despite the tantalizing experimental data. As for longevity, I hope we succeed, but we know humans are exceptionally long lived for our size already. Even with medical repair, we have to find a way to ensure that our brains don't deteriorate, as whole organ replacement isn't an option. Perhaps incremental stem cell neural tissue implants will allow continuity of self.

If we were to throw ethics aside, we could know if artificial raising of (newborn) babies by machines is possible, within a decade. I'd consider a communicating group of 5-10 year old kids without destructive behavior to be a success.


209:

Most of the recipes for stability on the generation ship seem to involve lengthening the "lifespan" of the colonists-- whether by freezing them or slowing aging.

How about trying the opposite direction- if possible, engineer the colonists for fast maturation and a quick senescence and death. Maybe a maximum age of somewhere around forty or so-- that way there's enough time to get trained as an engineer or scientist or politician or whatever, but not so much time that you get intergenerational friction.

Basically, you're increasing the ability of the population to evolve socially, possibly making them better able to adapt to changes (such as slow creeping disasters) as they happen.

Maybe freeze a few of the brightest for future reference.

210:

Shepherding the Sea isn't the aim of Sea Shepherd or Greenpeace -- the idea of sustainable harvesting of whales is definitely not on their agenda. The limited "scientific research" whaling that Japan carries out does not impact the population of most of the whale species including the previously endangered ones such as the blue whale, the fin whale etc. Same goes for the Norwegians ("Intelligent people need intelligent food!") and the Icelandic whalers.

Frankly there are no wild animals left, anywhere. Any "wild" populations exist on our suffrance and only because we wish them to exist -- smallpox got uppity and wham! Even the cute species are under the hammer; polar bears are cute if they stick to rgidly defined areas of the North but if they come south and enter civilised areas they get rounded up and deported or just shot, depending. Elephants get culled when the populations outgrow the reserve areas although it's done in a low-key manner with as little publicity as possible. Etc., etc. Now the chinese have solved the fertility problems of their panda population (at least in captivity) I expect an explosion in numbers followed by eventual control and even culling for the iconic symbol of cuddly wildlife.

That reminds me -- who was it selling fake panda fur hearthrugs, again?

211:

That reminds me -- who was it selling fake panda fur hearthrugs, again?

Don't know, but you might appreciate my way of dealing with people who try and lecture me about not checking that my tuna is dolphin friendly. Sooner or later, they ask a question like "Would you kill Flipper for a tuna sandwich?" I respond "No, but if I want a dophin steak, he's in trouble"!

212:

Its not just DNA and a cell you need but a dynamic environment. If I put a fertilised human egg in a tank of nutrients it wont grow to a baby, it needs a womb and that is a lot more complicated than a cell. You need to build a viable organ that is kept alive through a whole system of other organs.

If you know of any machines that are capable of teaching babies on their own and keeping them alive im all ears, youve presupposed that a ship will arrive around planet X and robots will go out and build everything they need. even if the ship itself just lands and becomes a big city you need machines to keep it going which means pretty advanced intelligent software and very capable machines.

I will give you this though, your idea may work if there was a known habital planet one where our immune system A works and B doesnt react to any super antigens and there is plentiful food for a hunter gatherer society. That way your ship could gestate babies by the thousand and raise them to locomotive children stage then release them into the wild. Perhaps after tens of kiloyears technological civilisations will rise from these offspring and crack the weird languages and codes in the old ship and learn where they came from.

But thats a whole bucket of magic wands in a handwavium shop on unobtainium lane.

213:

so im reading the jennifer morgue, was there a failed 1964 british lunar expedition?

214:

Forgot to mention that that last plan where children are spat out into the wilderness in the hope that some will survive to reproductive age probably counts as a crime against humanity

215:

Your post dovetails with what I thought about generation ships for a long time -- if it happens at all, it will not be representative of the mainstram society of its time, but will consist of people wanting to get away from that society.

A generation ship is essentially a fast-moving self-contained habitat. As you said (not in quite those terms), one can't even think of sending a generation ship until one has mastered self-contained habitats. And once space habitats (not particularly self-contained) become more or less widespread, every kooky cult or separatist movement will want one. In fact, they probably will master the techniques of self-sufficiency -- by dying repeatedly in all bad designs. And sooner or later, some will decide to take the Big Leap and leave "decadent sinful Earth" altogether.

216:

Not sure about magic wands, but a this point in technology general AI is less far away that, say, human habitats on the moon.

And human-like AI is not an interesting target anyway. I don't need your average chav in my computer, thank you very much.

OG.

217:

Charlie, with those terms of debate, I think you've boxed yourself into a corner. It looks like you need (at a minimum) autonomous AI, self-replicating robots or fusion power, plus the nanotechnology sufficient to turn space materials into things we can use, plus really good radiation shielding to protect whatever parts of the system are reproducing themselves at a molecular level (through biology or dry nano).

Without these, it's not clear that anyone (in the widest sense of "person") can live off the materials found outside Earth orbit, and without being able to live off the land, it's effectively impossible to justify something like a generation ship or even a big space habitat. Small to medium space habitats can be justified in the name of displacing national competence and conspicuous consumption, but I can't imagine even a Chinese American consortium building an O'Neill cylinder or equivalent just to demonstrate they can.

On a slightly different tack, the technologies dovetail. Good, light radiation shielding is necessary both to keep a reactor safe and to protect against outside radiation, while either a nanotech beanstalk or some sort of super-powerful/super-safe rocket is necessary to get materials to orbit cheaply.

Yes, I'm all for trying to do design with a minimum amount of hand-waving. But given that the fundamental problem is turning sunlight, rock, and ice into a human-supporting ecosystem in a high radiation vacuum while moving at high speed in freefall...what can I say? I think you need at least two magic wand assumptions to make it doable.

218:

Yes, though it's not well known. The project got as far as making lunar orbit (though not an actual landing) before it was cancelled for much the same reasons as the junking of Bletchley Park Colossus computers in '45/46, and the TSR-2 cancellation in '65 - partly to keep the US (to whom we owed an awful lot) sweet, but mostly because we really, really couldn't afford it.

Possibly the only such wonder-project of that era that did survive was the joint Anglo-French Mach-2 bomber, and that one managed mostly because they could build an SST on the same airframe.

219:

Working without magic wands is a useful exercise in outlining areas that need to be addressed as well as highlighting the difficulties involved. If we allow magic wands I may as well argue that a generation ship would be pointless once we invent ultra-low energy, ultra-long range worm holes cos then I could just step to other worlds.

Its hard to say what magic wands may be likely as well, I work in Nanotech and its nothing like the nanotech you read in most SF, talking about general purpose nanobots or universal constructors at our current level of technology is like talking about an automatic factory at the start of the industrial revolution. With AI we barely know what intelligence is let alone programming software more capable than us.

220:

I'm not lecturing anyone, but you seem to be ruling out digitized consciousness of any kind on a timescale of centuries. Equally, there seems to be an assumption that the biosphere to be carted around would have to be basically a complete food chain instead of heavily modified single-cell organisms in vats. I think someone already mentioned this last point, but so many of the numbers used in people's calculations seem to be based on to many assumptions.

What I think would be more realistic would be a small caretaker crew rotating between some sort of suspended animation to extend their lifespans, coupled with a larger colony population to be decanted on arrival. This larger population could then begin building habitats and agriculture (again, assuming technological advances to the point where farming consists of shoveling hydrocarbons into a vat with tailored microorganisms) and then start cloning babies for generation 2.

221:

Also: assuming that no 'magic wand' advancements in technology will happen seems to be at least as... off as assuming that any specific one will happen.

222:

Servants of their financial backers, the Merchant Adventurers of London, who as the dominant part of the joint stock partnership owned the colonists' labor and all the colony's land, livestock, and trade goods for seven years.

223:

Nobodies ruling it out but theres no evidence that it can be done and no viable mechanism of how it could work. Ditto for Biosphere in a can. Outside of science fiction (and by that I include a lot of popular 'science' like kurzweil) there are no good ideas on how to even begin assembling a kit of civilisation making techniques and machines.

224:

"Its not just DNA and a cell you need but a dynamic environment. If I put a fertilised human egg in a tank of nutrients it wont grow to a baby, it needs a womb and that is a lot more complicated than a cell. You need to build a viable organ that is kept alive through a whole system of other organs."

Agreed. But Charlie was prepared to accept that as doable.

"If you know of any machines that are capable of teaching babies on their own and keeping them alive im all ears, youve presupposed that a ship will arrive around planet X and robots will go out and build everything they need. even if the ship itself just lands and becomes a big city you need machines to keep it going which means pretty advanced intelligent software and very capable machines."

You're stuck on the immediate leap to high tech. babies survive in effectively stone age huts today. As long as there is shelter and warmth, they can survive. There must be a myriad ways to build shelter, from living in a cave, digging a hole in the ground to fully constructed building. More problematic is feeding babies. But seriously hard - not really.
Teaching machines? TVs + programming for language acquisition and basic skills.

"work if there was a known habital planet one where our immune system A works and B doesnt react to any super antigens and there is plentiful food for a hunter gatherer society. "

A known habitat and immune safe system is pretty much required for the generation ship colonists too. If they don't have that, they just make more space colonies. So why even go? As for hunter gatherer society, the same techniques of information encoding and gestation. This can be inside domes or more general "terraforming". We already have machines for farming if needed. But why cannot the ship provide prepared food - it would be part of teh training paradigm.

You would not need tens of kilo years for technological civilization to arise. Remember the ship has libraries of information, so you could get to basic industrial technology fairly quickly. But even if you did need that time, any arbitrary distance from Sol will mean that a fast ship will arrive with the necessary lead time to develop a civilization before a generation ship arrives.


225:

Yep.

However, let us discriminate between greater staffs of power and a mere entry-level magic wand.

The former probably includes anti-gravity, FTL drives, teleportation, and so on -- and also stuff like cheap'n'easy fusion reactors and high-grade AI.

But the latter includes, let us say, vastly more accurately targeted/effective/fewer side-effect cancer treatments (to mitigate the radiation problem from the other end), or affordable fullerene-derived materials with the tensile strength necessary to support a space elevator.

We don't have any of the entry-level magic wands yet, but we can see where they're going to come from and they are at the R&D stage right now: I think in both cases (cancer and space elevator materials tech) it's a matter of when, rather than if, we get them.

There are probably intermediate-level magic wands, too. Fusion power: given an adequate budget it's do-able. Even do-able within a decade, given a Manhattan Project style push with an unlimited budget (say, $5Bn in 1940 money: $100Bn today). The problem is (as Drexler noted) there's a return-on-investment desert between where we are now, and where we'd be with a mature fusion reactor technology: zero return until suddenly, Bam!

As for AI, I'm going to take a rain check on that one. We aren't going to get HAL9000 any time soon, but I'm not betting against useful applications showing up. Like, say, this thing called "google" ...

226:

Agreed. But Charlie was prepared to accept that as doable.

No, I simply wasn't willing to rule it out a priori as impossible.

It's one of those problems in biology that is best described as really, really hard. You need to look at the development of the fetal immune system, and human endogenous retroviruses, and a whole bunch of other rather esoteric shit that goes on in the womb and without which you end up with a baby with a compromised immune system and/or developmental abnormalities. Not just how to supply a placenta with oxygen and nutrients.

Moreover it's an area which is really hard to research in, because you start stubbing your toes on ethical violations once you propose growing blastomas to implantation and beyond in vitro. (Hint: yonder lie the anti-abortion protesters.)

227:

@ 188:

Well, my point is this: if you postulate a cylinder hab, then what are you doing with the space between your head and the axis of rotation?

Well, not a lot, except for storage close to the axis, ditto for any heavy machinery, and of course, probably there's going to have to be some sort of tension support of the cylinder itself.

Other than that, well, again, I don't know what you need for a stable, long-term, Earth-like ecology, so I would want to replicate the original as closely as I could. Maybe 10 km of space straight up to the axis is too much, but I suspect that 100 meters between decks is . . . optimistic.

Last, but definitely not least is the mass budget. An O'Neill cylinder ain't the Sugarplum Fairy. But adding in all those decks starts to really push up the mass. If you're going to do that, why not simply make more cylinders and have them travel as a fleet? Redundancy and all that. That way if Something Bad happens to one, say running into a few specks of gravel, the other ships survive to go on. There would be sociological benefits as well - the possibility for immigration is thus opened up, as are vacation spots, or even just ability to get away from the same old stinking place every once in a while.

As for why to build so big? Well, see earlier discussions about the minimum size of society necessary to maintain a technological civilization. My guess is that you can't maintain a starship unless you've got nearly enough specialities to build one in the first place.

Yeah, I was thinking of that too, which was why I said your setup was swanky. Me, I was just planning on crowding ten to one hundred million people into my dinky little can. Which I think is doable in terms of current population densities on Earth. But which might make the place a might claustrophobic.

Like I said, it's those unvoiced assumptions different people make which trips up the discussion :-)

If you're going to spend the money to send a generation ship in the first place, there's no point in not sending the very best.

Oh, certainly. If you're going to throw that much money into the business in the first place, you want to at least make sure the enterprise has a half-way decent chance to succeed. Most businesses fail within two years, and the number one reason is because they're under-capitalized :-)

228:

Clearly more lift capacity than can be provided by rockets is needed. Space elevators are pretty near to magic wand-type tech. Space fountains seem doable. No plausible lift technology would be able to lift the weight required, though, so an economy based on asteroid and comet/KBO/ice moon mining is needed. The long times needed for transfer of materials by efficient orbits puts limits on growth rates which push the possibility of an industrial base capable of building a starship out by a couple of centuries. The mining will have to be highly automated, but the need for short communication times to allow intelligent direction of the mining should give a strong reason to have humans out there.

Given the centuries needed to allow building an economy capable of building a starship without magic wands, it seems certain that by the time such an economy exists that some, even most, of those technologies that now seem like magic wands will long since have become old hat.

229:

@ 202:

Oh yeah I didn't consider it to be a ship just built and sent off by another polity. I was just using that example to illustrate how unlikely one is to be built ad hoc and sent off to escape whatever was going on in the solar system.

Here's a thought: while aliens coming to displace/kill all the humans has been done many times before, the lead times are usually measured in days to - at most - a few years.

Has anyone done a story where the aliens give notice for humanity to clear out immediately - any humans still resident when they arrive in the year 4011 in our reckoning will be shot on sight.

That strikes me as both giving plenty of time and plenty of incentive to build a generation ship.

230:

Ryan,

I think there's a huge difference between defining the minimum that's necessary to have a successful space colonization of any sort, and throwing the field open to say anything's possible.

Charlie's right: there are certain minimum technologies and possibly cultural norms that we don't have right now that we'll need to live in space. That's the minimum set of magical wands you need. If the wands don't work in reality, we're stuck on this planet, period.

That's a far cry from FTL or wormholes.

Personally, I disagree about the space elevators. I think the major problem there isn't the technology, it's the politic economics of putting the beast up. Considering that international companies are currently striving to turn fairly simple solar technology into tax-sucking boondoggles that (incidentally?) trash much of the desert wilderness left in this country, I dread what's going to happen when someone proposes a space elevator. Imagine this: Halliburton gets the contract, using a Texaco rig as the base, and they build it so that, if it fails, it will fall on the jurisdiction with the most lenient liability laws. Then they hire Boeing to build the launch vehicle. With (cough, cough) no cost over-runs whatsoever. At government expense, of course.

231:

Artificial Uterus - "It's one of those problems in biology that is best described as really, really hard. You need to look at the development of the fetal immune system, and human endogenous retroviruses, and a whole bunch of other rather esoteric shit that goes on in the womb and without which you end up with a baby with a compromised immune system and/or developmental abnormalities. Not just how to supply a placenta with oxygen and nutrients."

If only we weren't mammals. Even marsupial humans would be easier. :)

However I do think we can start research without ethical complications. Much of the technology detail is going to be solved with lower mammals, starting with rats. When we reach higher primate level, we are almost certainly nearly done. Given the infertility experienced today, and the legal issues of surrogate mothers, there is surely a medical driver to develop this technology. But however hard it is, I don't know that I would consider it harder than developing just the drive for the generation ship, and it is going to start development long before we have sol system habitats. We hugely underestimated how hard general AI is, so maybe the early successes we are having in genetic programming, cell development and organ printing are fooling us about the potential for these technologies. However, I do think that since these bio technologies have extensive applications on earth, we are far more likely to develop them in the near future than the more esoteric technologies needed for interstellar generation ship travel.


232:

@ 217:

Charlie, with those terms of debate, I think you've boxed yourself into a corner. It looks like you need (at a minimum) autonomous AI, self-replicating robots or fusion power, plus the nanotechnology sufficient to turn space materials into things we can use, plus really good radiation shielding to protect whatever parts of the system are reproducing themselves at a molecular level (through biology or dry nano).

Cough - Fermi Paradox! - cough.

On a slightly different tack, the technologies dovetail. Good, light radiation shielding is necessary both to keep a reactor safe and to protect against outside radiation, while either a nanotech beanstalk or some sort of super-powerful/super-safe rocket is necessary to get materials to orbit cheaply.

In terms of radiation shielding, "good" and "light" are oxymoronic. What works best in terms of volume is a high z-number. But you can also get the same result using a thicker shield composed of atoms with a lower atomic number. In any event, what makes a shield effective is the number of z's you can put between yourself and the radiation.

Yeah, there's a lot of talk about using strong magnetic fields to deflect the charged stuff. But magnetic shielding isn't light either. Nor is it effective against the charged stuff or the higher energy cosmic rays.

233:

"Most businesses fail within two years, and the number one reason is because they're under-capitalized :-)"

Actually that isn't really true. It just looks that way because eventually the losses from a non-viable business must exceed the assets. With infinite capital, all businesses appear viable... :)

234:

I think your mass estimates are too pessimistic.

Also, I gave a link earlier to a fusion rocket design with an Isp of 1.4Ms, 40% more than you were claiming for antimatter. With antimatter, one can get any desired Isp up to Isp 3E8 using raw gammas from postitronium or lower by mixing in variable amounts of reaction mass. If using antihydrogen the normal matter comes from the interstellar medium, then the effective Isp can theoretically be up to 2c.

The problem with antimatter is that it takes magic wand tech to produce it without throwing 99.9% of the input energy away. And a few other minor engineering difficulties....

235:

I think 2,000 years warming for the arrival of a generation ship type object would give us more than enough time to turn the solar system into a fortress, with a whole suite of dangerous weaponry poised to blow up everything approaching earth. I had a story idea about that once. Issues with defending the planet over that time period involve how you'd have decades between attacks, so the problems become 1) how to hold everything together politically and militarily over such a long period, 2) how to prevent friendly fire and potential blackmail situations, and 3) you end up with the E E Smith paradigm whereby no movable death ray can outgun a planet mounted death ray.

236:

More likely, in the absence of serious life prolongation tech we and our descendants would spend 1900 out of 2000 years ignoring the problem because we'll be dead and gone long before it arrives. Leaving the issue of fight-or-flee (build fortresses or generation ships) until the final century.

(Otherwise? Nicoll-Dyson Beam FTW.)

(Best estimate I've seen suggests that it only takes about 6-700 years of solar output to dismantle Jupiter gravitationally, and you can build the solar collectors to do it from the wreckage of the inner system in a mere century or so, given mature nanotechnology. At which point you've gut the material to build a Matrioshka Brain with an interstellar death-ray of planet-roasting power with a range in the tens to hundreds of light years.)

237:

One other reason I would prefer a seed ship than a generation ship is a moral consideration. Some on this thread have raised the issue of fairness to future generations living on the ship, even though a very large ship might be like living on a smaller earth. But a generation ship is committed - it must slow down in the target system whether or not the target planet[s] are suitable or not. Once there it must eventually die, or propagate with local resources. Perhaps prior unmanned probes have already sent back all the information needed for colonization, perhaps not.

A seed ship however, can make the decision to gestate, or not, it's human cargo on arrival. Only a viable planet would be populated. A seed ship could be left to die without concern for the unborn.
There is also a lot more opportunity for a seed ship to stage population. It could terraform areas with earth biota and ensure that these ecosystems are viable before humans are added.

238:

@230
This highlights that currently, the key obstacles aren't technological. They are sociological.
So the key solutions will have to be also.

239:
"Moreover it's an area which is really hard to research in, because you start stubbing your toes on ethical violations once you propose growing blastomas to implantation and beyond in vitro. (Hint: yonder lie the anti-abortion protesters.)"

But that may not be so much of a problem then an option; as some people might say, "what happens in O'Neil Colony Nanbang stays on Nanbang. Outsourcing your biomed research might be an interesting option, especially if the O'Neills in question have some souvereign status.

The protesters might try to ban Chinese or Korean goods, but that may be difficult with souvereign O'Neills with some Chinese or Korean capital...

240:
Forgot to mention that that last plan where children are spat out into the wilderness in the hope that some will survive to reproductive age probably counts as a crime against humanity

Please, could you show me any of the various declarations of Human rights that can be used in this way? Given the political interests part of said declarations, I seriously doubt anything like that, lest any nation be liable for an inequal education system.

On a related note, it'd be fun to sue some Evangelical homeschoolers or related nidwits..

241:

"I think there's a huge difference between defining the minimum that's necessary to have a successful space colonization of any sort, and throwing the field open to say anything's possible"

Yeah I agree, what I disagree with is throwing the word nano at something and proposing magic (thats a personal peeve). In the post I was replying to you suggested self-replicating robots. That type of technology is almost enough to create an industrial-complex in a can, just have one general purpose robot that can replicate and build specialised ones and your off.

242:

"You're stuck on the immediate leap to high tech. babies survive in effectively stone age huts today. As long as there is shelter and warmth, they can survive. There must be a myriad ways to build shelter, from living in a cave, digging a hole in the ground to fully constructed building. More problematic is feeding babies. But seriously hard - not really. Teaching machines? TVs + programming for language acquisition and basic skills."

Babies survive well in caves? are you kidding! it takes at least one full time parent to feed and raise a baby. And children learn by interaction, they can't learn language and other skills from TV.

"You would not need tens of kilo years for technological civilization to arise. Remember the ship has libraries of information, so you could get to basic industrial technology fairly quickly"

If the wild children eventually spawn civilisation then their descendents wont speak English and wont understand how to use the ship. Do you really think a cave man could use a 3D printer with its attached computer? It might speed up their once they've developed a primitive technological civilisation. Until then everything will be magic

243:

Hi Ryan,

Sorry to hit a pet peeve.

I'm a biologist,and so far as I'm concerned, we've been living with nanotechnology for the last four billion years or so.

I'm with you on the magic pixie dust aspect of nanotechnology, and I'm just as glad no one's throwing that stuff around right now. Show me the stoichiometry, I say.

244:

"Babies survive well in caves? are you kidding! it takes at least one full time parent to feed and raise a baby. And children learn by interaction, they can't learn language and other skills from TV."

At what point did I suggest putting babies to survive on their own in caves? You were raising barriers about needing complex structures to house the population. I'm simply refuting the premise that you need all the high tech extras. From a simple survival POV, it is believed that babies have been raised by wolves. Whilst wolves are very smart, they are certainly not human level intelligence. If children cannot learn from TV, then I guess we had better shut down those educational programs. There are even hints that some learning goes on in the womb. The issue isn't whether babies can learn from machines or not, it is whether you need "magic wand" level AI technology behind that machine education. I disagree, because I believe that the assumption that you need general purpose robots is incorrect. You use relatively dumb specialized machines instead, just as we do in industry, which is why we don't see all those 1940's era humanoid robots.

"If the wild children eventually spawn civilisation then their descendents wont speak English and wont understand how to use the ship. "

Your assumption is that machines cannot educate. Remove that constraint, and a very different picture emerges. And while Charlie wants a high tech civilization to be possible, it is clearly easier to create a lower tech pre-industrial civilization, perhaps equivalent to England somewhere between the Norman invasion and prior to the industrial revolution. Pre-industrial Shakespearean England is less than 400 years from the late C20th. The population at that time was estimated at 3-7 million, so we know that is probably more than enough to move towards an industrializing state.

245:

Yes, a pilot mission inside our own orbit would be indispensable.

But I also think that whatever your budget is for a starship, you'd be wise to spend more than half of it on a telescope.

To see an Asia-sized continent on Epsilon Eridani you would need a telescope with an aperture less than 7 kilometers across (math below). Your resolution increases linearly with your aperture, so the detail is mainly limited by your budget.

Of course, you'd want to do this with an *array* of light collectors in space, which can be thinner than gold leaf.

-----------------code-------------------
double km_to_m = 1000;// kilometers to meters
double ly_to_km = 9.4605284E12;// light years to kilometers
double nm_to_m = 1E-9;// nanometers to meters

public void calc()
{/* hypothetical diameter of a circular Asia-sized continent */
double Continent = 6663 * km_to_m;

/* distance from Epsilon Eridani. */
double Distance = 10.522 * ly_to_km * km_to_m;

double Wavelength = 380 * nm_to_m;

/* this is only an approximation, using a leg instead of hypotenuse, but it's a very
narrow angle. */
double Sine = Continent / Distance;

/* answer was: Aperture = 6926.0768372770945 meters */
double Aperture = ApertureDiameter(Wavelength, Sine);

/* answer was: ApertureKilometers = 6.926 */
double ApertureKilometers = Aperture / km_to_m;

/* ApertureKilometers is the answer, print it here. */
}


// Formula from the Rayleigh criterion:
public double ApertureDiameter(double WaveLengthOfLight, double SineOfAngularRes)
{
return 1.220 * WaveLengthOfLight / SineOfAngularRes;
}

246:

Hi Jessica,

I'm afraid living in space is involves both technological and sociological problems.

Anyone interested in colonizing space really should read up on the archeology of Oceania, because the settling of the Pacific is the nearest analog we have to colonizing other planets at this point.

Papua New Guinea was colonized over-water some 40-50,000 years ago, and they reached the main Solomon Islands perhaps by 35,000 years ago. About 3500 years ago, the Lapita people finally made it out to western Polynesia.

The interesting thing is that interim period. People were visiting the western Solomons and attempting to colonize them early on. They even introduced marsupials to the islands, so that they would have something to hunt. However, they didn't have agriculture, and their early colonies died out. Polynesia and Micronesia weren't settled until much later, when the requisite combination of highly transportable agriculture, sophisticated boats and navigation, and highly sophisticated fishing and sea-gathering techniques were bundled together. Even then, they went through a trial-by-fire period on atolls, where they had to readapt their (probably bronze-age) technology to take advantage of the limited resources of atolls.

But with reference to space, we're at the 35,000 years BP mark, not the 3500 years BP. We don't even have all the pieces yet, let alone a culture that integrates them properly.

247:

Or you could use gravitational lensing with much smaller collectors.

248:

222:
Servants of their financial backers, the Merchant Adventurers of London, who as the dominant part of the joint stock partnership owned the colonists' labor and all the colony's land, livestock, and trade goods for seven years.

-- in a 17th century context, "servant" has a specific and limited meaning and that ain't it.

In a modern context, the relationship would be somewhere between "employee" and "contractor".

They had very limited ability to get the actual settlers to do anything they very much didn't want to do. The area was outside the effective control of the English state.

Incidentally, the Merchant Adventurers didn't even get enough to cover their outgoings out of the Plymouth Colony and eventually had to settle for partial repayment.

Most colonial settlement companies went bust and most absentee investors in new colonies lost their shirts; this was extremely consistent over several centuries, though hope sprang eternal.

(Even Cecil Rhodes' BSA Company took 34 years to make a dividend; the only profits involved were those made from insider trading in its stock.)

The proprietary colonies like Maryland and Pennsylvania were deeply disappointing to their grantees too.

You could make money out of colonial settlement but it was very difficult to do so unless you were on the spot and could personally supervise things.

249:

@ 233:

"Most businesses fail within two years, and the number one reason is because they're under-capitalized :-)"

Actually that isn't really true. It just looks that way because eventually the losses from a non-viable business must exceed the assets. With infinite capital, all businesses appear viable... :)

Sigh. No, Alex. And this is easily found:

Statistics tell us that most small businesses fail in the first 5 years due to lack of capital. While this is true, in my experience the other reason . . .

A big problem seems to be that these startups incur unanticipated debt, so that even as they are turning a profit per the original model, they have assumed extra financial obligations. If these businesses had an extra $20K in seed money, they would have succeeded; they didn't fail because of a bad model, or because of inept management, or because sales weren't quite what they could be.

I only mention this - despite your well-known idiosyncrasies - because this seems to be a general principle. In fact the old, "Everything takes longer and costs more" principle.

250:

What if we reserved a corner of the space shuttle cargo bay each mission for a small booster engine and payload holding thousands of excess frozen embryos and launch them to the stars like the old Voyager probe? The payload's "passengers" would be shielded against background radiation and could use the deep cold of space itself to stay frozen. Like Voyager, each payload would contain an information disk describing Earth, Sol, humanity, etc. — and DNA instructions for the embryonic "passengers". It would also have a beacon to attract alien civilizations. A sufficiently advanced, space faring civilization (which would be capable of understanding what the payload was and be able to read the instructions) could create an artificial womb and bring the embryos to term. Or send along an artififal wombe that can be turned on when the payload arives 10,000s of years hence and robot parent analogs that would raise the first generation of colonists to maturity.

Crazy idea? Probably, but at least this would be a cost effective way to send our first explorers to the stars. It would ensure that even if Sol went nova tomorrow, there would be a chance that Humanity would survive somewhere out among the stars. Besides, a group of humans "hatched" and raised by a completely alien civilization might make an interesting SF story. However, given the outrageous energy requirements for traveling at a significant percentage of c, or the incredible amount of time for a living crew (sleeper ship or ark) to make it to the stars at a slower pace, this may be the only practical way for mankind to colonize the stars.

251:

Of course, you'd want to do this with an *array* of light collectors in space, which can be thinner than gold leaf.

I'm such a shitty proofreader. For clarity, read this instead:

"Of course, you might do this with an array of reflective light collectors in space, so that each can be as thin as gold leaf."

Also: each collector surface should be obsessively laser-scanned for irregularities, to compute them out of the final image.

252:

You seem to be assuming that other star systems will not only hold terrestrial planets, but planets with a compatible biosphere that humans with a low-tech infrastructure could exploit.

That's a very tall order: for 4 billion of the past 4.6 billion years Earth would have been pretty much uninhabitable by humans (due to a slight shortage of oxygen in the atmosphere), and for a good chunk of the remaining 0.6Gy it would have been pretty inhospitable (supercontinents tend to have extreme weather around the edges and gigantic, arid deserts in the interior). And that's on a planet that has a compatible biochemistry!

253:

I think you underestimate how big space really is. And how big a beacon you'd need for your payload to be detectable more than one astronomical unit away. And you overestimate how long a frozen blastocyte is likely to last in a high radiation environment. And how common intelligent spacefaring life is.

Hint: the Voyager probes have just recently passed the Heliopause and entered interstellar space proper, 13 light hours from Earth, over a third of a century after they were launched. They're currently taking around 22,000 years to cover a light year. And they're nearly the fastest things we've ever built. (I believe the New Horizons probe is somewhat faster: nine and a half years from launch to Pluto/Charon fly-by.)

254:

Charlie@150: Given that 80% of US citizens don't hold passports -- essential for travel outside the USA

I've always been a bit suspicious of that factoid. Until very recently (last year I think) Americans didn't *need* a passport to fly to much of their continent: Canada, Mexico and most of the Caribbean, and even now I don't think they require one for land crossings to Canada and Mexico. Now that passports are required for all international flights out of the US, I suspect that 80% figure is out of date now and will continue to fall.

Let's put it this way: how many British people would bother to get a passport if we didn't need one to go anywhere in the EU?

255:

You suffer from the usual "moving goalposts" affliction. The computer does a lot of things better than we can ever dream to do, for instance calculating or sifting through enormous masses of data. But each time a computer manages to do something better than the human, we redefine intelligence to exclude it.

And in practice, the computers from Babylon 5 (powerful tools, but only tools) are way more realistic than Hal. What's the point of programming a conscience, feelings, preservation instincts or other stuff like that when it does not make the tool better?

OG.

256:

I'm a biologist by training too! now im in medical nanotech. I agree, whenever somebody says nanobot i just think of a cell. The stuff i come across daily (nanoparticle delivery/detection systems for drugs and disease) doesnt come close to some peoples ideas of magic goo.

@255 Im not moving the goal posts or supposing that we need a human equivalent AI. Im saying there is no plausible way that software could raise a child and build a rudimentary habitat for it to survive in. So there are the goal posts a suite of software capable of:

*running and maintaining a ship
*building and maintaining a habitat
*gestating babies
*raising them to adults with a good education and socialisation

257:

I wish I could find the references that debunks lack of startup capital meme.

However, in lieu of that, the best way to think about this is "gambler's ruin". Any start up business will have a fairly random cash flow depending on a host of factors beyond the immediate control of the the owner. It is therefore like betting in a casino, or the stock market. The larger the stake, the less likely you are to be ruined (or the longer it takes if the returns are unfavorable). As a result, both gamblers and traders emphasize money management to "stay in the game".

While many business owners certainly desperately try to raise funds before bankruptcy, the argument that [lack of] capital was the problem is looking at the problem backwards. Businesses cannot raise more capital because it is usually clear that the business is just a money sink.

258:

...and thats what the Matrix story should have been

259:

The question of habitability (which you have explored in previous threads) is the same whether the colonists are trained nth generation or frozen embryos. In both cases, either the world is habitable, or it needs more terraforming, or it is unsuitable. It is not clear to me what different events transpire that favor nth generation colonists over the seed colonists.

Either nth generation colonists make planetfall, or they stay aboard ship whilst terraforming goes on, or they try to live on in the ship until...

The seed ship has the option to ensure either a terraformed planet for the new humans, or it can quietly die if the planet is unsuitable or terraforming fails.

If a planet needs terraforming, or is unsuitable, the colonists might very likely prefer to stay aboard their ship. Their expertise might help terraforming efforts for future generations (another millenium or more?), but is that a huge advantage? Maybe.

At this point we really have no idea what the likelihood of suitable planets is. However, within the next 100 years we can be sure we will have the catalog of earth sized, water bearing, oxygen worlds out to 5000 light years pretty well nailed down. (It is another issue as to whether they should be the targets or left alone). So either we will know that our ships are going to suitable, but hostile, worlds, or to lifeless terraformable worlds or just asteroidal resources. So you can choose the destination that is best suited to the payload.

260:

@200
I'd assume, in fact, that such a habitat was too large to build all at once, and needed, instead, to be built incrementally.

This leads to a requirement that it be economically viable during the building process. Sufficiently so that other projects will attach themselves to the already working habitat. (And probably modular enough that, at least while not under weigh, modular segments could disassociate themselves...and move on to another habitat. [I'm assuming that most small pieces wouldn't be even approximately sustainable for long periods of time. But that seems safe.])

This kind of consideration was kicking around in the back of my mind when I suggested that they made their living mining the Oort clouds. For normal propulsion I'm thinking of something that puts out on the order of 100 pounds of thrust. Probably an ion rocket that can use methane as a mono-fuel. (Maybe it splits the methane into H and C ions and shoots them out...but clearly it would need to use both positive and negative charges, so the exhaust stream is likely to recombine detectably. It's not a stealth drive.) With a good design this should be able to get the ejection mass up to around the speed of light before releasing it. It probably wouldn't need to be that fuel efficient, but a linear accelerator for ions isn't that tricky.

I may have underestimated the need for power in the engine, Most of the probes that use this kind of technique concentrate of light-weight, and I think they still use 10's of pounds of thrust. But speed will not be of the essence, at least until it's time to leave. And there would probably be a much higher powered drive for use when needed. Still, the design strength would all be to hold it together against centrifugal force. So you wouldn't *want* an engine that was too powerful.

I'm not sure if the caveat against easy fusion power means that I can't assume that the main colony isn't powered by a fusion reactors. (Actually, several. You *NEED* to have overcapacity for repairs, maintenance, etc.) But I suspect that fuel for fission reactors would be rather scarce out in the Oort cloud. I suspect that I'm not only assuming fusion reactors, but H-H fusion reactors.

OTOH, while the thing was in Sol-space it could apparently be fueled by a large solar mirror. (Another reason for low thrust engines!) This is presuming that the response that I got to an earlier query was correct. So the whole thing could be built before fusion reactors were feasible. It just couldn't leave.

261:

@ 205:
What shepherd do to their flocks is harvest them maintainably.

Might not be heartwarming, but it makes economic sense. And it keeps the sheep in being.

As to whether this matches their goals... well, I don't know enough about them to comment.

262:

Heteromeles @ 230
THAT is the exact problem.
I've just been reading a book on the collapse of the Brit Aerospace industry called "Empire of the CLouds" - which describes the failureas as 120% management (& guvmint) related - the dreaded "unions" only got away with iot, because management was so useless.
Now multiply that across all sectors.
And look at the USA today.

SoV @ 232
Hence using a re-formed asteroid as your slowbaot.
Thik about the shielding?

@ 254
SHengen
And paranoia and stupidity
But we ARE talking about guvmint here ....

263:

@ 235:

I think 2,000 years warming for the arrival of a generation ship type object would give us more than enough time to turn the solar system into a fortress, with a whole suite of dangerous weaponry poised to blow up everything approaching earth.

Yeah, and so when the aliens finally get here, every engagement ends within 30 seconds, with the human resistance obliterated. Meanwhile, the very few arks that do make it out of the system in time are just obsolescent military defense station cast-offs, ostensibly rebuilt as refugee vehicles as a sop to those liberal pantywaists who can't stomach a tough fight but which in reality were just kick-back schemes.

All die. Oh, the embarrassment!

Haldeman actually wrote a story like this recently. The generals were foolish enough to believe that resistance was not futile . . . When the first and only attempt to try the alien's patience was made, humans were put back into the stone age in less than a second.

No, you really don't want to listen to the military on this one.

264:

"I think the major problem there isn't the technology, it's the politic economics of putting the beast up. ....Imagine this: Halliburton gets the contract, using a Texaco rig as the base, and they build it so that, if it fails, it will fall on the jurisdiction with the most lenient liability laws."

Surely a falling space elevator will just wrap itself around the equator. I know nothing about African countries, but surely Brazil isn't going to be liability lenient? Definitely this is going to be politically tricky.

265:

@ 257:

I wish I could find the references that debunks lack of startup capital meme.

Given that it's widely agreed upon, easily researched (I just threw it into Google), and that you can't find "the references that debunks lack of startup capital meme", don't you think you're missing something rather obvious?

266:

what we need is more vons von neumann von braun von dyson von halen, on and on... and as far as voyager and pioneer, well did they ever really think about when something does come in contact with those discs!!!!!!!

267:

Re Space Elevators, et al.

I'm not convinced about a Space Elevator on Earth...EVER.

Mars and the Moon, yes. No problem. Just a lot of development. But on Earth things are stickier. For one thing the gravity is sufficient that passive materials may well not EVER be strong enough to lift additional weight. (Possibly there are ways to electrically increase the tensile strength.)

However there's another concept that hasn't got the PR that Space Elevators have. I know it as the Pinwheel. You take a heavy mass put it in a LEO. (You'll eventually want several of these.) Then you extent arms from it in a radially symmetric fashion. They need to be strong enough to support themselves and any cargo you want to lift, but they'll only be 30 miles long or so. They end with a hook to which a cargo pod can be attached. To load them a pod carrier flys a cargo pod up to the place where the pod can be hooked off. (This is above most atmosphere. I'm not sure, but say 30-40 miles up.) It doesn't, however, need orbital velocity. That's supplied by the orbiting weight. And, as with all skyhooks, you want to lower as much mass, on an average, as you raise. So the cargo pod is a lifting body that can be steered, but has minimal power. And it's just dropped right before the next cargo pod is attached. It flies itself to a landing field.

Pinwheels don't require more strength than current materials can supply. They don't cut the cost to orbit quite as much, but they slash it much more than in half. (I forget the estimated figures, and of course what they would be exactly depends on fine points of the design.)

268:

im pretty sure there already working on the space elevatoer
ive read some articles on the net

269:

I've worked with sheep... um, let me rephrase that and put it in context. As a lad, I helped out on my uncle's hillfarm as unpaid skivvy labour. Sheep were brought down off the hilltops and overwintered on the farm where the lambs were born and it was occasionally my delight and privilege to keep the stupid things from killing themselves in a dozen different ways.

You know how you see green fields of sheep and lambs in the late winter and early spring? Lots of lambs with their mothers, awww. What you don't see are the barren ewes that didn't catch from the rams put to the flock the autumn before because those ewes have already been shipped off to the abattoir, no second chances. Round about April the male lambs are castrated because they're going to the abattoir in the early summer once they've put on most of their growth from the grass feeding. A couple of the healthiest best of breed males are kept uncut to cover the ewes later, probably including their mother as it's kind of difficult to keep them separated at rape time. That coupling is likely to lead to infertility or stillbirth and the mother getting sent off to the Big Shiny Building next year but them's the breaks kiddo, it's business nothing personal. Mutton pie anyone?

There's fleecing, where the sheep get sheared and dunked in toxic chemicals such as organophosphate anti-tick dip that would give them cancer in a few years but they don't usually live that long so it doesn't matter. Then it's autumn again and rape rape rape till the cows come home or the ram collapses through exhaustion. Thus is the Circle of Life completed, if you're a sheep. And Sea Shepherd can sink in a fire for all I care.

270:

No I don't. :)

It is just very difficult to dig through the noise without time. There are many popular myths about business, some deliberately promulgated. Just because they are popular, doesn't make them correct.

If you cannot change your perception about under capitalization, ask yourself how you would recognize if a start up business was over capitalized?

271:

They are called sky hooks. One was featured in our host's "Saturn's Children". I think they are fairly well known... :)

272:

Hans Moravec and Robert Forward named them in a paper written in 1980, where they discussed the design parameters of synchronous ("space elevators") and non-synchronous skyhooks. Here's a later draft by Moravec from 1986. It's well worth reading this paper to dispell a lot of the BS that's been spread about skyhooks and elevators.

273:

That's the fun question. Kim Stanley Robinson's elevator wrapping itself around Mars is a great image. Thing is, the elevators they are talking about for Earth are much thinner, so they *should* (heh heh) burn up in the atmosphere. Partially? Entirely? It's a really ugly dynamics problem that's probably going to cost a couple million to model well. My guess is that the bits will hit somewhere, rather than having a line wrap. Still, positioning the bottom of the elevator is a spectacularly ugly problem.

And that's without the probability of getting hit by orbital debris, and the newly discovered threat of thunderstorms emitting antiparticles from above the clouds, and weakening the line as the storms go by, and the joys of having a long piece of string twist and kink when an elevator is zipping up at a few hundred klicks per hour.

But I'm cynical. All I can say is that riding the beanstalk isn't going to be like standing in an elevator for a week. I suspect it's going to be more like spending a week on a roller coaster. With freefall at the end! Cool!

274:

The swanky habitats aren't going to leave the system barring something really unpleasant (Like Accelerando's vile offspring) and we're not considering weakly superhuman AI today. Spotting a biosphere would be a reason to go look, but not for colonization, since we have a post-planetary civilization already, they don't need planets, so the mission would be one of scientific inquiry.

Conservationists would be extremely opposed to anyone landing anything not totally sterile on said biosphere, I would imagine. Unless social mores swing back to a more 19th century view of nature being at our disposal. So a swanky habitat may consider taking off for a closer look if they're already used to life in the outer Oort, but I still see smaller research missions being more probable.

Anthropocentrism be damned, I suggest just directed panspermia, shoot water bears and deinococcus radiodurans in every direction, maybe with some engineered extra payload in their genomes it would be possible to pack the seeds of a more complex ecosystem in a population of bacteria for it to unpack if it finds adequate conditions somewhere out there. Leave a watermark easter egg message if it ever evolves sentience just to mess with their heads/nerve clusters.

This is a considerably longer term project but it's cheap, doable with current science* and the only variant of shooting babies into space that I don't find morally abhorrent.

275:

An article in the WashPost says that the sheep thefts in Briton are mostly because of the high cost of food now.

276:
the joys of having a long piece of string twist and kink when an elevator is zipping up at a few hundred klicks per hour.

Not going to happen. The tape or cable has to be under a great deal of tension for the elevator to work at all; hundreds of tons for even the minimally useful elevator. An elevator cab massing less than one percent of the total mass of the cable is not going to make it twist perceptibly.

277:

Charlie writes: I don't think that's practical in terms of space colonization. There's no "there" there -- nothing to breathe, nothing to eat, an environment that will kill you dead in seconds if your isolation procedures fail.

-- sure, the extrasolar environment is going to be far more hostile than colonizing the Americas... though as I noted, most of the colonists there DID die quickly.

But by definition our capabilities will be vastly greater then too, which probably more than balances out.

Eg., if you've got the energy supplies needed to move large masses over light-years, why bother with biological means of getting air? Just blast the oxygen out of whatever compounds come to hand; H20 is rather common anyway.

I have great confidence in three basic principles:

a) in getting anything important done, character trumps cleverness. Better to have as much as possible of both, but if you have to pick, go for bloody-minded determination over skill at symbolic manipulation.

(Writers and other intellectuals tend to be extremely resistant to this one, for the obvious reasons.)

b) elegance buys no yams; and

c) if your problem doesn't immediately yield to being hit with a hammer... get a bigger hammer.


278:

269: You know how you see green fields of sheep and lambs in the late winter and early spring? Lots of lambs with their mothers, awww.

-- well, yeah, I've worked on farms and with animals too. For the animals it usually (and in the end, invariably) sucks.

So? We're predators; we don't raise the animals for their (individual) benefit, we raise them for our own purposes, which usually involve killing and eating them. I'm cool with this.

In -genetic- terms, being a domesticated animal raised for human purposes is an extremely successful evolutionary strategy.

Sheep and pigs are not in any danger of extinction. Not as cushy as being a domestic cat, but still a lot more secure than being, frex, an eland.

279:

Given the difficulties, we'll probably terraform Mars (and possibly Venus) and have lots and lots of large habitats and whatnot by the time we get around to trying interstellar stuff. If we do at all.

At that point, both our capabilities (in terms of energy, basically) and our knowledge will be enormously greater than now. In many respects, they'll be greater than we can -imagine- now.

Like, if you can terraform Mars, what -can't- you do?

280:

I think you're being unfair to fusion power. No way that it's in the same category as FTL drives . . . at least we know fusion is possible. But even if I had a choice between fusion and space elevators, I might pick fusion as the lesser magic wand.

281:

Sorry, my imprecision. I wasn't thinking of the elevator causing the spinning and kinking, I was thinking of the line swaying and the elevator capsule being along for the ride. One end will be in the ocean (which, erm, moves) and the other end is in space (where it's going to need some ability to keep station, regardless of its orbit), and various things like atmospheric drag, jet streams, electrical storms, and space debris will affect the line itself constantly. The space elevator line might have to shimmy just to stay in place and avoid all the crap.

Stories to the contrary, I don't see a space elevator standing still. It's going to sway and ripple, and it's probably going to twist and untwist at least locally. Even if the lateral movement is a few hundred meters on a 50,000 mile line, that's a hell of a ride for the people in the elevator capsule.

282:

Reading through the multitude of comments ranging from how to keep the meat payload viable and still able to reproduce, to how to power the interstellar habitat over such great distances, I decided to throw another monkey wrench into the works...the electronic systems...
For a journey of any length you'd need to carry a fabrication facility on-board just to replace worn out components...just do a quick read on bathtub curves and today's "modern" electronics... The interstellar ship might as well be using vacuum tubes based merely on component longevity. So the less parts the better, and as much standardization of components as possible will also be a requirement. Another interesting item is that the current trend in solder (namely lead-free solder) will have to be reversed to avoid tin plague which occurs more rapidly at colder temperatures...

284:

I'm going to go back to the original analogy about putting the armor plating everywhere else.

If you are going to send out a generational ship, it should be the very last thing to be sent. The supply line (spare parts/extra fuel for refueling/extra anything) needs to be established first. Unmanned supply ships go first at different velocities and the generational ship catches up with them as it travels to its ultimate destination) This would eliminate a great many obstacles/problems that I've seen presented here. I thought of this independently and then began to wonder if Arthur C. Clarke had something in mind like this when he wrote Rendezvous with Rama.

285:

This whole rejection of magic wands is totally against what the SF market wants. We want plausibly justified and logically coherent magic wands. (And forget characters. Sure, they're a necessary evil, but if we were interested in people, we'd be out talking to them, not reading SF.) So up with nano, AI, the singularity and general applied weirdness.

In that vein, here is a line of thought that hasn't been sufficiently exploited: Investigation of a ''quantum ramjet'' for interstellar flight H.D. Froning, Jr., Senior Staff Engineer, McDonnell Douglas Astronautics Company

286:

Marilee @ 275
Nah
Given some rural areas in this country, and the deprivation in inner-cities - you know - they're stealing the PRETTIEST ones?

S M Stirling @ 277
For a well-know SF author, with some excellent work, this post is totally off-the-rails.
Your list of criteria sound like those for a (ahem) "successful" WWI General, like Falkenhayn or Nivelle.
Oops.

@ 285
Yes but WHICH "magic wand do you want?
The conventions of SF usually allow ONE per story - sometimes referred to as the "McGuffin". Yes, I know, that has another meaning, as coined by Hitchcock - a local boy from around here see these pictures - so there.
More than one wand is usually deemed "unfair", and renders the story "fantasy", or something.

287:

Terraforming Venus is probably impossible, in the absence of real magic, Harry Potter grade at a minimum. (It's not just the atmosphere; you've got a weirdly long diurnal cycle and no plate tectonics, so you can't establish a deep carbon cycle and the surface liquifies spontaneously every 200M Earth-years or so -- as in, lava everywhere.) At best, it turns out that 80% N2/20% O2 is a very efficient airship lifting gas in Venus' atmosphere (CO2/H2SO4 is dense!) and there's a zone in the stratosphere that's at roughly 1000kPa pressure (Earth-atmospheric equivalent) and 20-30 celsius, so you can probably build airship cities and live inside the lift bags. As long as you understand that a leak will (a) let in the clouds of anhydrous sulphuric acid, and (b) if not fixed, will lead to your cremation.

Mars is another matter, if you can do heavy engineering there. I'd start by building air dams -- probably nothing more than suspended plastic sheets -- around the deepest ends of Valles Marineris, then roof them over with transparent plastic film. Once there's something in place to reduce leaks, it's time to work on filling it with air to roughly Earth pressure at 7Km altitude (extremal for human adaptation, but just barely tolerable -- it's comparable to the higher regions of Tibet). Given the depth of VM, up to 7km below mean Martian surface, the retaining film to keep the air in won't have to be terribly strong; with good design it won't need suspension cables either, as it'll be held up by air pressure. Once it's up, you now have a greenhouse with (eventually) a breathable gas mix that has nearly as much land area as France and Germany combined.

If you've got an area that large where you can live and work without needing a space suit, you've got room to establish and grow the facilities you need in order to move on to terraform the rest of the planet, which is going to take multiple centuries at a minimum.

On the other hand, I wouldn't underestimate the challenge of erecting two or more air dams 200km long and 5-7Km high, and then roofing over a 2500km x 200km rift valley with plastic film!

288:

I'd agree with the basic point: the elevator itself won't be rigid. But, from the point of view of the passengers in an elevator car, are the movements going to be noticeable? How big are the accelerations going to be? How does the movement compare to the speed of the elevator car?

It's not as simple as a guitar string, but there's a local suspension bridge with carefully-placed lumps of metal to control vibrations in some of the lighter cables. It doesn't seem crazy to have a space elevator with a structure attached part-way up, which is where it is for similar reasons.

289:

I'm not sure that the "One Magic Wand" rule is quite so rigid. FTL travel, for instance, sort of implies cheap power, and a few other things. It's a whole package of magic wands, but most stories handle it as a single item.

An important test is maybe how the story depends on the detail magic wand. FTL can be a general hand-wave, no more significant to the story than the propulsion of a railway train. Miss Marple doesn't care how the train works: it doesn't matter to the puzzle of 4.50 From Paddington. A hypothetical SF murder mystery might use a particular form of FTL drive to isolate the mystery (consider the Traveller jump drive as such a plot tool) but you couldn't use it to replace the snow-blocked railway line of Murder on the Orient Express.

290:

A useful book you might want to look up is:

Apocalypse when? : calculating how long the human race will survive / Willard Wells. Berlin ; Springer, c2009. 9780387098364 (pbk.)

Which takes a statistical look at long terms survival rates for humanity, using a model based on business start ups and theatre runs.

291:

@246
Heteromeles,
You are right that there are both sociological and technological issues.
I just think that right now, even if we solved the technological ones, the sociological ones would prevent implementation, but if we could solve the sociological ones, our technology capacities would start to increase unimaginably faster.
Our host raised the question of how large a population has to be to support the entire science and technology needed for space travel. Whatever that size is, it needed to be that much larger if much of the population is under-educated and much of the work we do is a waste.

292:

#218 - This isn't entirely SF - the Scottish Museum of Flight has (in storage, since they've got an SST crammed [used advisedly; the tailfin is inches below the roof truss] into one display hangar) a more or less complete Black Knight, which was certainly an Earth orbital capability.

On the "military SST", I have an image of a plausible model being a 1:144 scale SST with the smaller of the 2 mission pods from the Italeri 1:72 scale B-57 Hustler hung below it. Would anyone, particularly OGH, see a significant issue with that? (note that AFAIK the "type" only appears in prose so far)

293:

#284 - When ACC wrote the original "Rendezvous With Rama", quite possibly; when he and/or Gentry Lee wrote "Rama Elebenty", not so much!

294:

#Various ref colony ships - I'm wondering why no-one else is mentioning "Slow Train to Arcturus", where you have several habitat modules built into a string, boost the whole lot up to speed, then, when you get to a colonisation system, detach and brake the end module, whilst the other N-1 modules continue at the same (or greater, by use of orbital mechanics) speed to the next destination.

Like when I mentioned "CageWorld" above, I'm going to ignore the plot; the thing that's relevant to our discussion is the BDO the plot takes place in.

295:

#288 - I see where you're coming from. If we postulate that the "beanstalk" has multiple cables, we might even think in terms of a "mass damper", where the cables are connected by horizontal tubes containing masses attached to the cables by springs? The concept has been used race cars (where rules permit or at least don't ban it) for the last few years.

296:

Black Knight was, if I read it right, only ever sub-orbital, though getting that far is a good step on the way to LEO.

From LEO to higher orbits is another large step, and getting out to the moon even further.

(As for the SST, I was thinking of the use of Concorde in The Fuller Memorandum.)

297:

Black Knight was used to put the Prospero satellite into orbit, I think, and it's still up there as far as I'm aware. (Though the telemetry was turned off in 1996.)

http://uk.ask.com/wiki/Prospero_X-3

298:

Not Black Knight but Black Arrow carried Prospero into orbit.. BA was a proper launcher, but its maiden flight was five years later. In 1964, you had BK.

(The UK space industry is pretty successful, but it's mostly concentrated on the payloads rather than the launchers.)

299:

I do note that a Blue Streak/Black Knight combo was posited as a launcher. Who knows what might have grown from that?

(And can anyone tell me what the point of Ask.com is, when all it ever seems to do is to give you the Wikipedia page anyway?)

300:

(Magic wands) Where would you put spacecraft capable of running without supervision for two hundred years?

301:

#296 to 299 inclusive -

It's been a while since I last got to see the booster, so I could have Knight and Arrow confused, but I'm sure it was claimed to be orbit capable, and you're correct about the proposal to use it as a booster for Blue Streak.

Oh and I had "The Fuller Memorandum" in mind too; arguably you could just use Concorde with a military serial, but that would be boring to look at. So I thought "I have a spare small B-57 mission pod; it should fit under the belly without rubbing the ground, and it's designed to be M2 capable.

302:

As for the SST, I was thinking of the use of Concorde in The Fuller Memorandum.

I have a vague memory that that wasn't entirely made up by our host - there was some work, how far it got I don't know, on militarising Concorde with a weapons bay for carrying the Skybolt air-launched ballistic missile.

303:

Blue Steel, probably, rather than Skybolt.

304:

Could be either; Blue Steel was designed for semi-conformal carriage, and there'd be more than enough space for 2, maybe 3 under Concorde, using the baggage hold, and probably enough clearance to mount Skybolt pylons under the fuselage instead.

305:

Three points on generation ships

1) Population. Population size change with time. So you need somekind of feedback loops to "depopulate" or repopulate the ship. When population reaches a certain limit the mission is doomed. What those loops are and how they work. I have no idea.

2) Social structure. People are interested in status and prestige. One solution to this is make some places inside the ship more preferable to live than others.
This thing may promote a kind of monarchy. So there's a revolt and leaders get hanged. Usually no big deal, because leaders rarely have a good technical skills, but they do have good people skills. And technical types are not usually people persons. Or leaders.

3) Getting to destination. Let's think that ship that arrives to destination has an utopian society. Why would anybody want to leave the ship. It's their home. So you need to kick them out. Kick them out of a paradice. What if the ship is a dystopian society at arrival. People have no means to leave or have lost necessary technical skills to use landing crafts. They are prisoners of hell.

One issue about orbital elevators or skyhooks. They are gonna be a choke points in the future. As orbital flights and needs to get there increases, there's a limited amount of these things (elevators and hooks) that you can use. Also loading and unloading these things becomes problematic.

306:

Quite often prognostication is overridden by events and offspring end up doing things their progenitors only dreamed about but not in the way they thought it would ever be done.

Here's an idea for interstellar travel that is physically possible (probably) and can transport human beings from star to star and allow them to gradually populate an area of the Milky Way. The only necessity is the first step, that of establishing long-term colonies of humans in space, whether on planetary surfaces (with or without terraforming), moons, asteroids and habitats.

The colonising effort moves outwards driven by wanderlust, a search for resources, religious or philosophical belief, whatever. New habitats are built in the Kuiper Belt, move out slowly over generations into the Oort Cloud and then one of these habitats finally makes the move into the Cloud-equivalent region of a neighbouring star. Several more millenia pass as that habitat's offspring gradually move down into the liquid-water zone of said star. The interstellar voyagers have finally arrived, hundreds of thousands of years from now never actually having planned to go there in the first place. A lot of habitats will fail along the way, people will die in accidents and from lack of resources and odd diseases, radiation, wars and other traumas but unless there is an extinction event that takes out all intelligent life beforehand the interstellar jump will be inevitable (ASB interventions are something else).

Whether these colonists several hundred millenia from now can be described as human as we would understand it is another matter.

307:

Para'last - An Earth geostationary orbit has a circumference of about 265_000km; the limiting factors will be the longitudinal separation that can be achieved between the ground stations on the Equator at 40_008 km, how wide and deep the orbiting cylinder can be (unknown by me) and how many cars can be going up and down from each ground station at any time. Rememeber we're not dealing with a lift shaft that can only contain one car. There's no obvious reason why you shouldn't have "express" passenger cars and "slow" freight cars on multiple cables on a single "beanstalk" configuration.

308:

There's an artist's impression of a Concbomber/Discorde in the programme for the RAF 50th anniversary celebrations in 1968.

309:

Substitute "the next valley" for the various "astronomical areas", and that's not a bad description of how people spread prior to the start of "active exploration" in probably the Neolithic.

310:

Cheers mate; I know someone who'll probably have a copy they can scan for me now I know where to look.

311:

"Several more millenia pass..."

I think your time scales are out. As Charlie already mentioned earlier, prior to the Horizon mission, our fastest spacecraft are doing about 1 light year/22 kilo years. Space colonies that are being constructed of Oort materials are not going to be going as fast, plus their directional travel may be more like a random walk. So at least 100K years to more than a 1M years to arrive at the next star?

312:

Why colonize/terraform Mars or Venus when we should be going to Ceres?

http://www.pagef30.com/2009/04/why-ceres-might-be-better-location-for.html

As a matter of fact, why colonize anything at the bottom of a significant gravity well?

The most valuable piece of real estate in this or any other solar system may not be the Earth or any planet for that matter. The most valuable parts are the asteroid belt and Oort cloud. All the mineral riches (and essentially free energy from solar powered stations) that an advanced species could want is available without the great expense of dragging them up from the bottom of Earth's gravity well.

313:

And who says we have to make big jumps from one star to another? The space between stars may inlcude dozens or hundreds of brown dwarfs:

http://www.scifi.com/sfw/issue183/labnotes.html

What if space is littered with these failed stars, scattered between the bright ones like a stellar Polynesia, making interstellar travel a series of short hops, rather than a single gigantic one? What if a simple fusion reactor carried just enough fuel to push a spacecraft to our solar system's Planet X in reasonable time? What if it could refuel there, harvesting just enough hydrogen or deuterium or helium to limp along to another dark neighbor, and another, and another? Granted, it would take a long, long time to get to Alpha Centauri that way, and probably a much, much longer time to find a planet somewhere that looked even remotely like our rain- and sun-drenched Earth. But given the likelihood of tidally warmed moons, and the obvious possibilities for life there, we may just find that the cold, dark spaces are where most of the action is anyway.

Brown dwarfs can have Earth sized moons and give off enough heat to allow for liquid water:

Discs around brown dwarfs typically weigh about one-tenth of the mass of the star itself, so in this case it probably contains one or two Jupiter masses of available planet-building material. "I'd speculate that it could build a Saturn, or maybe a few smaller Earth-sized planets," says Luhman. What is more, these would-be planets could be habitable. The surface temperature of the mini brown dwarf is about 2000°C, which means that any planet 1.5 to 7 million kilometres away could maintain liquid water. The disc probably straddles this range. Luhman hopes to find out whether even smaller objects - perhaps as little as five times the mass of Jupiter - can reign at the centre of nascent planetary systems. "It's still an open question as to how small you can go, but hopefully we'll be able to answer that soon."

Instead of long term voyages like the European explorers we should be thinking about island hopping like the Polynesians.

314:

Let's see, according to NASA, the elevator has to climb 35,786 km to GEO, not 50,000 miles. Anyway, if you want to climb that distance in a day, the elevator car needs to average 1491 km/hr, but I don't think a supersonic elevator is practical, if only because I don't even want to think about what the shockwave would due to the line itself. So it will take a minimum of two days (at 745 km/hr) to climb to orbit, and even if it took seven days, the elevator would still be averaging 213 km/hr, if I did the math right. That's about the speed of the Shinkansen bullet train in Japan.

At that speed, any rippling is problematic, and aside from hurting the passengers, you also have to insure that both the elevator car and the line can take the lateral strain of something moving that fast trying to separate itself from the line.

On the bright side, if we can figure out how to make a light-weight elevator car that climbs at bullet train speeds and doesn't kill the passengers when the line sways, I'd say that every country with a bullet train can easily retrofit their tracks to be totally earthquake proof. It's a similar problem, just horizontal. Right now, of course, Japan stops all the trains when they detect an earthquake coming.

315:

I'm surprised that you think terraforming Venus is probably impossible and would need Harry Potter level magic to do.

1. Diurnal cycle. Yes it is long, 243 days. Inside the Earth's Arctic Circle it is over 180 days. Last I heard, there was plenty of life withing the Arctic Circle, especially the oceans.

2. Atmosphere. It doesn't need magic to deal with it. Indeed we can speed up Venus' rotation and strip off the existing atmosphere with glancing asteroid impacts. Nothing magic here, although you won't be able to colonize for a long time :)


3. Carbon cycle. What you say is true, but applies equally to the space colony/generation ships. Yet they sound quite Earth-like to me. Carbon cycling will just not be deep, and may need technological support. Certainly no magic needed.

Finally add sun shades to keep the insolation down to a nice level to aid cooling, add water from comets, leave on slow simmer as organisms are added. The water might even help restart plate tectonics and get deep carbon cycling going.

It isn't going to be quick, but it should be doable in 1 million years or less. Perhaps you mean it needs magic to do within a few millenia.

316:

re:"Unmanned supply ships go first at different velocities and the generational ship catches up with them as it travels to its ultimate destination"

No it can't, since it will be traveling at a much higher velocity as it passes them.

317:

At this point there is no evidence for brown dwarfs closer than alpha Centauri. This may change when the WISE mission releases its results and data next year.

Until new data arrives, we have to assume that the nearest visible stars are the main targets, although it is also probable that the Oort cloud model suggests small bodies may be found at very low density a significant fraction of the way between those stars.

318:

Umm, the Arctic (and Antarctic) aren't good comparisons for Venus, because most of the animals that live there migrate away from the poles, and many of the life forms that remain are pretty good at hibernating.

I think Venus has great potential as an extreme engineering site, and the best reason to colonize Venus is to set up chemical plants on the surface, to take advantage of the high pressure, high temperature, highly acid conditions. What would be a hazardous waste site on Earth is normal for Venus. They would have to be teleoperated of course, and you'd have to figure out how to get stuff up and down safely.

Mars has the similar problem of having an inactive core, which means no deep carbon cycling and no magnetosphere. The later is probably the biggest problem, because even with an Earth-like atmosphere, it will be a more radioactive environment. Plus, without the magnetosphere, the atmosphere will decay, so Mars would have to be re-terraformed periodically just to keep it livable. It's the solar system's ultimate fixer-upper.

319:

Love the quote on the possibilities brown dwarfs bring. Waiting for WISE to announce its findings is almost excruciating as even one brown dwarf closer to us than Alpha Centauri will change the way we view our part of the galaxy forever.

On that note, I recommend calling them brown dwarf stars even if they technically aren't quite the same. Calling them sub-stellar objects just makes them sound like...well, objects. A good term for astronomers to use, but calling them cool stars is the best way to describe them in is short a time as possible.

320:

Let me bring up another issue that generation ship and singularity stories ignore. Semiconductors have a limited lifespan.

In 2002 I had a conversation with Geoff Landis in which I asked him whether the increasing process density of semiconductors was benefiting the space program. The answer was no that they were stuck at roughly the 8086 generation of processors. Finer pitch semiconductors are subject to soft and hard errors because of radiation in space.

Note: One implication of what I'm pointing out is that Moore's law, which all the singularity predictions are depending on, disappears in space.

Semiconductors have what is called a bathtub failure curve. It is characterized by a higher level of initial failure that declines to a low steady state then rises as the devices reach end of life. Average lifespan will be affected by environmental conditions and packaging failure can have a significant impact. (The semiconductor manufacturer I used to work for was sued by a number of hard drive manufacturers because of large quantities of premature failures. The root cause turned out to be that the vendor of the packaging compound the chips were packaged in changed the formulation without properly testing it.)

The consequence is that a generation ship will require its electronic systems to be rebuilt during the journey. Spare parts will be good only if they are completely protected from radiation.

I live about five miles east of the Austin Samsung fab. It is currently being expanded with a new 300mm line and will be the biggest fab in the US when completed. Something like it is just one part of the kit you will have to take on a generation ship. You also need to manufacture passive components and fabricate circuit boards.

321:

"the Arctic (and Antarctic) aren't good comparisons for Venus, because most of the animals that live there migrate away from the poles, and many of the life forms that remain are pretty good at hibernating."

I wasn't exactly thinking about putting polar bears on Venus :( The point is that life exists within the Arctic circle, including fixed plants, hibernating mammals (is that a problem, they hibernate in temperate zones too?), non-hibernating and non-migrating marine life. Then we have deep ocean life below the photic zone all over the planet that have no diurnal light cues.

In other words, a long diurnal period is not a constraint for higher forms of life. The worst case would be that a solid surface became so hot that primary producers would be burned off the surface and be unable to recover when it cooled for next "season". But terrestrial plants have solved that problem after wildfires with seeds, wind dispersion could be sufficient for some plants to maintain a hold, and animals would have to burrow or migrate. Oceanic areas would be less affected by extreme heating.

But if we are going to throw rocks at Venus, we can surely place sunshades to mitigate heating, so I see this as a non-issue. Indeed we can place both orbital sunshades and mirrors to create much shorter diurnal periods if we need to, without resorting to heroic measures.

So I see Venus' slow rotation as a solvable for terraforming.

I think the real problem is the dense atmosphere. Apart from blasting the atmosphere off the planet, are there better ways to replace it with more benign gases at reasonable pressures? Can we freeze out the gases with shades and remove or convert it to rock (that would need a lot of Calcium [and water] to make limestone and gypsum)

322:

How about calling them "dark stars"?

That sounds way cooler.

323:

It's funny how he does a lot of work pointing out the advantages of colonizing Ceres (instead of Mars or the Moon) but he never points out that one of the really big advantage of all that water (compared to the Moon, or L2 or elsewhere)) is that it makes it incredibly easy to build an efficient and cheap water shield for stopping radiation.

324:

I would argue that rather than colonization, Ceres offers a really good, low delta V water resource for the inner solar system. Use the water for life support, propulsion, radiation shielding of spacecraft, etc, etc. This will bootstrap space exploration by massively reducing costs.

325:

Personally, I think if you're going to dump cheap fusion, then the best place to colonize is Mercury.

The idea is that you put lots of big solar/EM power generators on Mercury, and any settlements you build under lots of rock. The settlements suck in energy all day, then when the sun goes down, the uncover some enormous lasers and beam power to the rest of the solar system.

The real centers of culture would be the midnight trains (I'm thinking road trains, not rail), that circumnavigate Mercury once per day (if Wikipedia isn't lying, they'd only have to average 11 km/hr east to stay at the midnight position). Think Dubai on a train, coming to each settlement every 58 days or so.

It's not a bad system for getting rich, harvesting energy where it's quite abundant and shipping it to where it's needed. Get water and other resources shipped to Mercury in return, and power a whole trans-system civilization from sunlight.

326:

Erm... "WISE" ?
Tried google ... nix.
References, please?

327:

Wide-field Infrared Survey Explorer

http://en.wikipedia.org/wiki/WISE_mission

328:
but I don't think a supersonic elevator is practical,

You needn't worry too much - once you've covered the first 100 km, you're not going to have much shockwave after that. And a Nozomi-speed elevator would take 20 minutes to do that.

Then it could start to accelerate.

Freight elevators may well go slower, because of power requirements, but you're probably better with the passenger ones of running them as fast as you can.

329:

I was thinking of a larger number of millenia than two or three when I said "several" but your point is well-made, that it could take the sort of timescale between Erectus and the pinnacle of human evolution, namely myself, to get one of these habs into another solar system. The neat thing is that the spread of habitats will be omnidirectional through the densest plane of the Cloud (with the richest resource pickings) meaning the colonisation of a second star system will occur a few tens of millenia later. Then the third one, the fourth... Brown dwarfs would be a bonus for spawning new habitats but it would probably slow down the spread somewhat. Laser launcher systems at such locations which might make probes possible (see "Mote in God's Eye" for details) giving the hab drivers more of an idea what they're aiming for.

330:
it is also probable that the Oort cloud model suggests small bodies may be found at very low density a significant fraction of the way between those stars.

The current Oort Cloud model predicts fairly high density: large objects (20 km diameter & larger) a few 10s of millions of km apart (see #88 above). At a guess that's not a whole lot less dense than the asteroid belt, but distributed over a much larger volume1. Also, most of those objects are supposed to be primarily ices, just what colonists are going to need most for air, water, food, and fusion power.

1. IIRC the asteroid belt is estimated to have a total mass of a few percent that of the moon; the Ooort Cloud is estimated to 20x to 200x the mass of the Earth.

331:

Can we step back and look at the engineering challenge of running something at jet-fighter speeds while it's stuck to a moving line? The problems I see are A) where's the energy coming from to get the elevator moving that fast? Is there a fusion plant on each end, or something? Or are we just assuming monster fly wheels to store all the kinetic energy of the car coming down to power the other one up? B) assuming the line sways (the whole point of this post) even by 0.003%, that's still a one kilometer lateral shift. Depending on how fast that line's moving laterally, keeping the elevator car moving that fast without derailing would be tricky, and would require a really, really tough carriage. Remember that derailing a space elevator is bad. C) assuming a rapid lateral shift of even a few tens of meters, keeping the passengers from smashing into the bulkheads would be difficult. Keeping them from whiplashing would probably be harder. D) Finally, detecting and dodging space junk at those speeds also gets interesting.

As I said, going up or down a space elevator would be a wild ride. If one of them gets built, I suspect the cars will move a lot slower.

332:

An interesting near term research project is to launch telescopes into the Oort to map out the distribution of bodies. It wouldn't surprise me if their distribution was anisotropic and offered such higher density "paths" to other stars.

If (and it is a huge if) there was a way to capture such bodies while in flight, they might offer a way to collect the fuel for fusion starships, IOW, a Bussard ramjet using icy bodies instead of hydrogen. I know that the BR was proven unworkable (drag > power) but perhaps this approach might not be. Collecting objects that you would want to avoid like the plague seems counter intuitive to me, but perhaps not with the appropriate technology.

333:

Leelo-Dallas multi-reply...

On power:

Fission is just fine. Power density (energy/mass) of fission is about 22% of fusion; see for example:
http://www.nuclearweaponarchive.org/Nwfaq/Nfaq12.html


Convenient Energy Content Approximations
Fission of U-233: 17.8 kt/kg
Fission of U-235: 17.6 kt/kg
Fission of Pu-239: 17.3 kt/kg
Fusion of pure deuterium: 82.2 kt/kg
Fusion of tritium and deuterium (50/50): 80.4 kt/kg
Fusion of lithium-6 deuteride: 64.0 kt/kg

For power systems for long duration, think Oklo:
https://secure.wikimedia.org/wikipedia/en/wiki/Natural_reactor

"few hundred thousand years" at 100 kw average output. You can configure reactors that will run at low average density for very long times. It's not that difficult, you have to budget out fission poison isotope buildup and diffusion and decay rates and find what steady state density you can maintain under what conditions. But it's not hard to do. Nature did.

For large colonies / ships - if you're assuming spin gravity, then keep in mind that tensile strength of the outer envelope, and structural mass fractions for the structure, are the limiting factor. With normal metals at reasonable alloy strengths, and 1 G spin, you get something like a few miles diameter (10 km?) before those get to be very serious problems.

For Venus - the problem is getting rid of the oxygen. The carbon's harmless, but if you can't get rid of the oxygen you end up with a hyperflammable atmosphere. Best solution seems to be dump methane or hydrogen on it and end up with a deep ocean. The energy required to spin up the planet and centrifugally force away the mass is impractical compared to the energy to mine large amounts of hydrogen off (say) Neptune, transfer it to Venus, and let nature take its course. Diverting comets might be energetically easier but the total cometary mass influx may be too small over practical periods of time. Neptune has plenty of material.

Fabbing - DMLS (laser sintering) is really pretty much approaching fabrication magic, in terms of capability for metals it can work with and end part strength characteristics. It's slow, and max physical sizes are sort of low now, and power input is higher than one might want. But if you need anything from a custom made mechanical watch to jet turbine or rocket hot-gas contacted mechanical components, it's your gear.

Nice part? You can probably grind up metallic asteroids and magnetically separate out the metal, and then without further ado feed them into DMLS and get usable metal, though processing alloys further will certainly help.

Reducing the materials process to grinder + magnet + DMLS is probably roughly the space manufacturing equivalent of magic, and we are probably right about there. Someone needs to try the experiment (sacrifice some meteor fragments as input material for actual tests) but it seems like we're about there right now.

Precursor studies - I second the "Just drop a colony down under the ocean and see what happens". You can get the whole totally isolated systems phenomenon that way if you want, CHEAP, and simulate everything but zero-G for decades or centuries or millennia that way. Hard part would be financing and finding the volunteers, though some geeks who are focusedly indoors people might be willing to try it.

334:
where's the energy coming from to get the elevator moving that fast

There are competitions going on right now for various designs for elevator cars. The most common power supply is free space microwave or optical transmission from the ground to the car. The obvious constraints for beamed transmission are keeping the beam width small enough to get all or most of the beam power into the receiver, making the transmitter and receiver track each other for maximum transfer, designing the receiver for maximum efficiency of conversion to motive power (probably electrical, to drive DC electric motors), and making sure that any beam power that gets spilled doesn't damage or degrade the tape or cable. It helps that the cars are being designed for fairly low speed: 200 to 300 km/hr in vacuum.

assuming the line sways (the whole point of this post) even by 0.003%, that's still a one kilometer lateral shift.

Given the amount of tension on the tape/cable, and the speed of sound through it (probably at least 4 or 5 times the speed of sound at STP, I would think), it seems like the amount of shift per km of length is going to be small, that is, the lateral shift of 1 km might be expressed over the whole 50-100,000 km length, and the amount of shift over a short distance, say the length of the car, would be pretty small.

335:

The concern I would have is the useful lifetime of the semiconductor fab equipment. Ultrahigh resolution UV photolithography or X-ray lithography equipment is quite delicate and sensitive to shock, vibration, and the evil eye. And the reactor vessels for molecular beam epitaxy and all the other fun chemical processes get eaten up over time. In fact, you wouldn't dare throw the waste products away; you'd need to recycle them if you plan on keeping the fab operational for centuries, and that means a lot of careful storage and processing of some very nasty substances.

336:
An interesting near term research project is to launch telescopes into the Oort to map out the distribution of bodies.

You don't need to go that far, you just need to to have one telescope with a large enough orbit around the sun to get decent parallax on anything out to the edge of the Oort cloud. Since that maximum distance is about 0.3 parsec, Earth orbit is fine, and in fact WISE is intended to make such observations (they're looking for Nemesis, the hypothetical dwarf star that might be sending large numbers of comets into the solar system every so often). WISE will only operate for a few months because it's an infrared telescope that requires coolant to function, and it will run out before the end of the year. Putting a longer-life visible light or near infrared telescope in the Sol-Earth L2 point would put the scope away from near-Earth lights and objects, and allow mapping the Kuiper Belt and Oort Clouds to a much greater resolution.

337:

That's essentially what I was proposing in #11 and #88 above, though I just talked in detail about the first few steps. I think getting to the edge of the Oort Cloud would take less time than you might think: there's no reason that colonists have to wait until they've maxed out the population density of one settlement before moving on to set up another. In fact it's unlikely they would wait that long if the history of population migrations is any indication.

The average distance between usable OCOs could be less than 50 million km (the current estimates say its roughly 10 to 20 million); it wouldn't be unrealistic to hop over a longer distance to the next settlement, leaving intervening objects for later fill in. Say each long hop is 200 million km, and a new long distance settlement is started every 25 years (one generation, so the old fogies can stick around while the new kids get to move on), then on average the surface of settlement expands by 8 billion km every millenium, or about 1 million years to the edge of the Cloud. If instead of going a given distance you go a given percentage of the current distance from the sun (assuming the density of OCOs decreases with distance), the Cloud could be filled much faster than that. Assuming we start at the inner edge of the Cloud (2,000 AU from the sun) and go .001 of the current distance from the sun on each jump, getting to the edge at 1 llght year will only take 40,000 years.

338:

I'm surprised that you think terraforming Venus is probably impossible and would need Harry Potter level magic to do.

Sigh. You missed the biggest obstacle of all -- the fact that the topmost layer of the planetary crust is in thermal equilibrium at roughly 600 celsius. Has it occurred to you to wonder how long it's going to take several trillion cubic kilometres of rock to cool radiatively from 600 celsius to something humans can walk on?

I think your 1 million Earth-year time frame is a little optimistic; I'll grant you 10 million years should suffice.

But now consider that our species is 0.2My old, evidence for culture is 0.07My old, writing is 0.005My old, and our life expectancy is between 0.001% and 0.0001% of the time frame we're looking at.

We're going to need physical immortality -- pretty much the real deal, resurrection of people who are killed by accidents included -- before we can even think about building social systems that can manage a project of that duration. Interstellar flight is actually easy compared to terraforming Venus.

NB: you appear to not understand the difference between the relatively-well-understood atmospheric carbon cycle, and the deep carbon cycle, in which carbon is locked down in sedimentary rocks and subducted between tectonic plates. (Which is a process that certainly doesn't apply to generation ships!)

339:

The surface of Venus would cool quicker if you broke it into little pieces with more radiative surface -- see "The Venus Belt" by L. Neil Smith for a radical terraforming concept. Pity it uses up Ceres in the process though.

340:

Hmm. If you can cut it off from solar energy, with a solar shade or similar, then the outer 100m would cool by about 300 degress per year, at 300 degrees - it would reach human survivable temperatures within a year.

Still, it's probably still harder than interstellar travel.

341:

Does your calculation take into account heat transfer from deeper inside the crust, or does it treat the crust as a 100 metre thick entity? Remember, we're talking about an entire planet that's little more than a blob of lava -- okay, a complex, stratified gravitationally self-binding blob of lava -- 6,050 Km in radius!

342:

Assuming 2 watts for a cubic meter as my energy transfer coeficient (which is 'stone' somewhere on the web), the flow rate for 300 degrees of difference over 1km would be 0.6 watts per square meter. Which, compared to insolation, doesn't even matter.

(wikipedia has the thermal conductivity of stone as 1.7 here http://en.wikipedia.org/wiki/Thermal_conductivity).

343:

Going back a bit upthread. The Convention on the Rights of the Child is the big one that would prevent dropping children in the wilderness. Acceptance of this convention is close to universal with the USA as one of the few hold-outs, so no hitting their homeschoolers on the head with it.

344:

Okay, that was a snapshot of the devlopment, wasn't it. Lets see - for 50m, that's 12w, and I'm not using calculus at all, which would be a considerably better estimate. 12 watts still isn't that much, although this is only really indicative. The internal heat of planets takes so long to leak out it was originally used as the explaination for the internal heat, rather than radioactive decay.

345:

But this planet too is little more than a blob of lava of about the same size, with a 100 km crust on top.

As I understand it, the big problem with Venus is that that its atmosphere is a very effective heat insulator - hence the surface is hotter than that of Mercury, despite much much less solar energy reaching the ground. Not only is it working as a greenhouse, even in the absence of any solar irradiation it would slow down the cooling of the planet. So, to cool Venus, you need to thin that atmosphere as well as shade it. Given that it appears there's no convection of Venus's interior, cooling might be quicker than otherwise expected.

(IANAPlanetologist - which is what we need at this point.)

346:

OK, what of a 100 km thick layer?

347:

#304, 308 and 310 - My mate had a JPeg of the illustration and sent me a copy, which has 3 pylon-mounted Blue Steels on the wing leading edge, forward of the main gear bays.

348:

Ah, I think you're looking at heat transfer via conduction. Which works internally within the mass of rock, but then we reach the surface and have to lose heat via black body radiation from the cloud tops at 600 celsius. Even if we strip the atmosphere away, we're dealing with radiative cooling, not conduction or convection (which are vastly more efficient):

https://secure.wikimedia.org/wikipedia/en/wiki/Radiative_cooling

Here's a page on the Kelvin cooling time for the Earth:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/cootime2.html

Plugging in the figures for Venus at 900K in the handy calculator, the time for the surface to cool to 300K is 0.46 x 10^15 seconds, or about 146,000 Earth years.

(Whoops: I just noticed the simplifying assumption that the sphere is homogeneous and this is cooling the entire sphere to a uniform temperature of 300K -- it's an assumption that work well for balls of hot gas, not so well for planets with distinct boundary layers in their hot cores.)

349:

No, if a temperature gradient over 50m of 300 degrees means only 12watts per square meter, anything below say 200m can be ignored.

350:

Just a strange idea, but...

It was already mentioned that any terraforming is going to have some problems with too much oxygen; personally, I think sulfur might be a problem, too, but well, let's start with that.

So, what about a system that uses heat pumps to get the heat from the surface and the atmosphere to said oxygen, and then catapults the superheated oxygen into the extraplanetar medium; I don't know if that's something for when sveral laws of thermodynamic are on holiday, especially since the heat of this system might rise the temperature of the atmosphere even more, but well, just an idea.

351:

@ 313:

What if space is littered with these failed stars, scattered between the bright ones like a stellar Polynesia, making interstellar travel a series of short hops, rather than a single gigantic one? What if a simple fusion reactor carried just enough fuel to push a spacecraft to our solar system's Planet X in reasonable time? What if it could refuel there, harvesting just enough hydrogen or deuterium or helium to limp along to another dark neighbor, and another, and another?

Along the lines of your speculation, what if space instead of being mostly hard vacuum and a few atoms per cc was considerably clumpier out to say, a quarter of a light-year from your star?

What happens when the odds of hitting something the size of a BB rise to something like 1 in ten per square kilometer of surface area per light-year?

Cough - Fermi Paradox! - cough.

It might be - speculating of course - that until you get well away from a given star, the maximum safe top speed is not 0.1 c or 0.01 c, but 0.0001 c.

No way to tell at this point, obviously, save for some rather broad upper bounds already established by observation. I could see a naturally occurring "Crystal Sphere" scenario where there are lots of aliens trying to break out of their home system, but the only way to do so is to clear out a number of corridors several AU across and a quarter of a light-year long.

Of course, you couldn't do this from outside the system; too much effort to sustain across a supply chain of several parsecs chasing too little reward. Species who want to enter into commerce with the Galactic Federation have to do the clearing themselves. Only then can those kilometers-long Highliners bearing culture and civilization, ivory, apes, and peacocks, approach Earth. Since this is a centuries-long task, minimum, it also selects for those species who can think long-term and who are not likely to obliterate themselves through some racial defect of character. No Pak, and no Kzinti(sp?), nor no Moties to have to contend with.

352:

Ahem: we're talking about cooling rock. Which shrinks as it cools. Around a core of hot liquid rock. Which isn't shrinking. Sounds like a recipe for vulcanism to me! I'd want to cool more than the first 200 metres before I'd be happy about landing and starting to build there -- make it more like the first 5-10km.

353:

@320:

"Let me bring up another issue that generation ship and singularity stories ignore. Semiconductors have a limited lifespan."

[snip]

"The consequence is that a generation ship will require its electronic systems to be rebuilt during the journey. Spare parts will be good only if they are completely protected from radiation."

Given the ever increasing cost and complexity of fab lines, and the range of feedstocks they need, semiconductors as we currently know them are a no-no. There are two possible alternatives though, ink jet printed plastic semiconductors, just starting to come on the scene, or a return to good old fashioned valves (tubes, in trans-pondian).

It should be remembered that in the 60s, when the US was using semiconductors in space craft, the USSR was still using valves, and they'd got some pretty neat miniaturised ones. Valves are far more radiation resistant then semiconductors, and IIRC miniature valves have been used in artillery shells, so can withstand high gees and vibration.

With modern technology, why not use the sort of construction used for microfluidic systems to make multiple very small valves on one substrate, using field emission cathodes? Evacuating them is simply done by taking them outside to seal. Apart from machining (or possibly printing) the structural part, the only requirement is to be able to put down controlled layers of metal, much as is done in current semiconductors. You don't need massively pure monocrystalline wafers, strict control of dopant levels, or ways of handling the very unpleasant chemicals used in fab lines. I think it's got to be worth considering, and has a great "old is new again" feel to it.

Disclaimer: it's several decades since I did any work in electronics, so could be talking through my hat. I have no doubt some kind person will inform me if I am. :-)

354:

@ 333:

On power:

Fission is just fine. Power density (energy/mass) of fission is about 22% of fusion; see for example:

"few hundred thousand years" at 100 kw average output. You can configure reactors that will run at low average density for very long times. It's not that difficult, you have to budget out fission poison isotope buildup and diffusion and decay rates and find what steady state density you can maintain under what conditions. But it's not hard to do. Nature did.

I've never understood how this meme of Fusion - In Space! got its hooks so deeply embedded into the science fiction/space community. Could it just be something along the lines of forming an unreasonably good opinion of it at an impressionable age? My favorite spaceships from the Golden Age were the Scavenger rockets from "The Martian Way", for example: nothing fancy, just a "proton micropile" that heated up water to high, but not unobtanium rocket nozzle high temperatures. The background assumption seemed to be that this was some sort of cheap and easy tabletop fusion device with negligible radiation worries . . . unlike the real deal :-(

It also seems to me that as far as desirability for space use that no matter what, fusion machines will be much more complicated than a fission reactor (of course, young Dolph Haertel will now probably construct one in the family garage out of coat-hanger wires, glass bottles, auto parts, and some cheap electronics.) That's got to be some sort of consideration, no matter how advanced the state of the art.

For large colonies / ships - if you're assuming spin gravity, then keep in mind that tensile strength of the outer envelope, and structural mass fractions for the structure, are the limiting factor. With normal metals at reasonable alloy strengths, and 1 G spin, you get something like a few miles diameter (10 km?) before those get to be very serious problems.

This is another reason I stick with the Rama plan; I assume that Clarke being who he was and the scientific/engineering connections he had was well aware of this problem, and was informed enough to know that you didn't necessarily need any more support than was shown for a structure of that size.

But even so . . . I'm guessing that for safety margins if nothing else, you'd have to have some sort of support cables running up to the axis.[1] Do you have any numbers for this? I know how to calculate hoop stress from basic physics, but my strength of materials mojo is barely enough to be aware that there can be problems in this regard.

This also brings up the intelligent use of resources problem. All other things being equal, I'd rather use what I had to make ten cylinders of a thousand square kilometers each as opposed to one with ten thousand square kilometers. Redundancy.

Reducing the materials process to grinder + magnet + DMLS is probably roughly the space manufacturing equivalent of magic, and we are probably right about there. Someone needs to try the experiment (sacrifice some meteor fragments as input material for actual tests) but it seems like we're about there right now.

!?!?!? Very nice, if true. But on that one I'm afraid I'd have to see some cites before I believe it.


[1]IIRC, the minimum cylinder size is already more than a mile in diameter to reduce coriolis effects to an acceptable level. Has recent research upped the revs?

355:

I'd be interested to know how they overcame the reason that valves were generally dumped in favour of semi-conductors - that valves had a horribly short operational lifetime. With the earliest computers, there was initially a question as to whether you could get a calculation completed before any of the valves burnt out, whereas with discrete transistors this was not a problem.

With transistors, you have the dopant drift problem. But with valves, you have to have an element able to emit electrons - and I suspect it will be tricky to build an element such that it will not slowly sublimate to the point of breakage, even though you may be able to build it small and robust and cheaply.

356:

Someone mentioned that cosmic radiation was a problem. But what if we think it another way, as an solution. We built this generation ship in a following way

1) inner surface is filled with small villages and resources in basic form like ore, water, trees and such. Population 10000 people.

2) then there's a shielding and structure aka ground. Under shileding there's a water reservoir aka fuel.

3) outside is composed porous material that lets water to seep outside to the engines. Engines are radioactive materiel like in "natural reactors". Water turns into steam and provides propulsion.

In essence the whole ship is an engine. To steer it you need to put high tech system on the back end of the ship. Why so low popualtion density at the start. Population grows exponentially and is low at low numbers and get higher at high nuimbers. If the colonist are lucky they are at the civilization size at arrival.

357:

That design's just not going to work. Reason: you're basically using steam as reaction mass, just like the Space Shuttle. The Isp is about three orders of magnitude too low for even a slow generation ship. Building a structure capable of ejecting water vapour -- or even ionized hydrogen and oxygen nuclei -- fast enough to do this particular job is, shall we say, rather challenging.

(I've been ignoring your earlier postings because they're so wrong they're just plain annoying, but you've finally overcome my ignoring-annoying-things threshold.)

358:

How much water is in the atmosphere? Venus is too dry to have plate tectonics and unless there are oceans of water in the atmosphere it may never have them. Supposedly, this is the Earth's fate too in a few hundred million years as the planet slowly drys out.

359:

Your original statement:
"It's not just the atmosphere; you've got a weirdly long diurnal cycle and no plate tectonics, so you can't establish a deep carbon cycle and the surface liquifies spontaneously every 200M Earth-years or so...".

So obviously I was replying primarily to your issue of the diurnal cycle. I hope I have disposed of that.

Let's next deal with the issue of deep carbon cycle as that seems to be a bother to you.
I'm going to use your human species lifespan as the argument against you here. If you only want the ecosystems to run without technology (and why should that be a constraint for terraformers?) then the deep carbon cycle is hardly a requirement on that time scale. If terraforming efforts failed after t kilo years, is this a disaster? It's like arguing that we cannot practice modern agriculture because phosphorus would be exhausted within a few seasons (and we are "running out" even now).
I suspect that we have different meanings for terraforming. I consider a environment that is suitable for humans and sustainable for a finite time (that is very short in terms of planetary lifetimes) sufficient. IOW, we could terraform the moon, but it won't last without intervention.

Now let's address the big issue, heat. Notwithstanding various comments below, I believe that left to itself, an atmosphereless Venus would take many millions of years to cool sufficiently to a more earth like temperature profile. No argument there.
But just like the deep carbon cycle, do we actually need that? Can we cool just X meters of depth across some fraction of the surface instead? IOW, we actively cool some part of the planet's surface actively (with water?) and let the rest of the surface radiate away the heat? This can be enhanced with solar sunshades if required. For the biota, this is like living on a plain surrounded by impassable volcanoes. Living ares can be patchy, they don't have to be uniform across the whole surface. I just don't accept the "all or nothing" premise, instead of a "just good enough" one.

In practice, I think O'Neill was right, and that we are still practicing "planetary chauvinism", which is just unnecessary. We could build far more real estate with colonies more easily than any collection of planets can offer. Your reference ship with the land area of the US attests to this. If it was just a colony, in earth or solar orbit, it would already be offering more lebensraum than a partially terraformed Venus, with probably a lot less heroic effort. I really don't think we need to recreate Gaia.

360:

@306, 337

Consider the time frame of 40K yrs (to slowly colonize to the edge of the Oort). 40Kya we were living in caves. 4kya we were bronze age agriculturists with some cities. 400ya we were at pre-industrial Elizabethan England. 400y in the future Charlie's generation ships will have been launched (maybe). The technological singularity may have come and gone.
4000 years in the future the singularity will definitely have come and gone if it is correct (and assuming humans are still around as a technological species). We will have pretty full control of biology and may well have speciated. 40Ky in the future?

I just don't see a future in which a fairly static process of building colonies that slowly migrate outwards is likely. Even our 400y future may be a lot more surprising to us, than our civilization could have been envisioned by Shakespeare.

361:

There may be convection of Venus' interior, but it is manifested on the surface only as volcanic eruptions.

But we know so little about Venus that there are likely to be a lot of surprises when we eventually get geologic data.

362:

As for the diurnal cycle: no. Talk about winds and temperature cycles before you convince anyone. The fact that some species have adapted to 120 days of relative daylight isn't sufficient.

As for any crust cycling of any element, things get interesting. Without any subduction and vulcanism, stuff tends to get bound where it's unavailable to the biosphere, meaning productivity goes down and the biosphere slowly grinds to a halt. Australia is a great example of this in action today. Additionally, Venus currently has little or no intrinsic magnetic field, so you need not only a sunshade but a magnetic shield to a) make the planet habitable, and b) keep the atmosphere from getting blown off by the solar wind.

And that's without figuring out how to cool the planet through black body radiation.

As I noted above, Venus is better with an industrial ecosystem than a Terran biosphere. You can do a fair amount of useful work with a hot acid bath, and you certainly have different issues with toxic chemical disposal.

363:

@355:

"I'd be interested to know how they overcame the reason that valves were generally dumped in favour of semi-conductors - that valves had a horribly short operational lifetime. With the earliest computers, there was initially a question as to whether you could get a calculation completed before any of the valves burnt out, whereas with discrete transistors this was not a problem."

[I'm presuming you're replying to me @353.]

The late Tommy Flowers would have strongly disagreed with that. What killed valves was turning them on and off (especially the cathode heaters). Flowers simply designed Colossus not to be turned off, and it worked wonderfully.

I presume the USSR simply engineered the valves to be more reliable. We are talking about the space program and military use after all, cost per valve isn't the big factor that it is in consumer items. The avionics on the Mig-25 were mostly valve based as well, at least in the beginning.

For the generation ship case, you'll note that I suggested using field emission cathodes in the reworked version. These work at ambient temperature ("cold emission"), and use field strength to rip electrons out of the tips of sharp spikes that form the cathode. This technology has been suggested as a possible next generation CRT display technology and it has various other uses. You can use metal or buckytubes as the cathode material. Building very small triodes this way ought to be possible. OK, it's probably 3-4 orders of magnitude larger than current semiconductor circuitry today, although that could be improved on, but it's a robust, relatively simple technology, and circuitry can be built in 3D, rather than the 2.5D of semiconductors.

364:

"As for the diurnal cycle: no. Talk about winds and temperature cycles before you convince anyone. The fact that some species have adapted to 120 days of relative daylight isn't sufficient."

While this is obviously not the whole story, I am not going to get into an argument about a system that neither of us (or indeed anyone) can answer satisfactorily. The best I can do is show counter-examples to claims to try to refute them.

"Without any subduction and vulcanism, stuff tends to get bound where it's unavailable to the biosphere, meaning productivity goes down and the biosphere slowly grinds to a halt. Australia is a great example of this in action today."

You are arguing for natural processes that are sustainable over geologic periods of time. I thought I made it quite clear that the I did not consider those as valid premises. Think farming rather than wilderness, and human history vs. 1 million years.

I don't disagree with the other issues you raise, but I don't think you can invoke these as unsolvable (or requiring magical technology) either.

I will just let this argument rest by invoking Clarke's 1st and 3rd laws.

365:

You didn't like the idea of sending out re-supply ships first and sending the generation ship second? You make it sound like an impossible task to snag a resupply pod along the way, whereas I see it entirely feasible if one applies a small amount of imagination...on a small scale think Space shuttle - robot arm, or the distinct possibility that the actual generation ship might have various other spacecraft attached to it for any number of purposes. External hull repair? Joy rides to relieve the tedious boredom? Picking up supply caches sent ahead? I'm not pushing any limits here, just trying to extrapolate today's technology as it might apply to such an endeavor.

Almost entirely forgot this difference:
In English "valves", in American English "vacuum tubes" and I'm babysitting some systems that are still running vacuum tubes (valves) after 20+ years...
Things I've noticed in this nuclear research facility about long-running electronic systems...Wire insulation prone to cracking and deteriorating. Solder joints devoid of solder due to tin plague. I'd love to get permission to rewire a lot of it, as the plant recently got a license renewal for another 20 years by the NRC. (50 years now since first criticality)

366:

There may be convection of Venus' interior, but it is manifested on the surface only as volcanic eruptions.

That's in the short term.

In the long term, there's some evidence that every few hundred million years the entire surface of Venus liquifies, then re-solidifies: supporting evidence includes the odd lack of eroded features on the surface (suggesting that just about everything we see down there -- using cloud-penetrating radar -- is less than 700M years old).

367:

Indeed. But we aren't going to worry about that in the lifetime of the human species and any possible terraforming for same. :)

I'd be interested to know if anyone has any thoughts on possible new mineralogy under Venus' geologic state.

368:

Really? I could have sworn that earlier on this thread you were gaily waving off objections to projects denominated in hundreds of thousands of years.

369:

Well, see, we use Maxwell's Demon to harvest all the heat on Venus to build the generation ship, then we make it inertialess, and use the pressure of sunlight and the solar wind to pitch it into interstellar space in a perfectly steerable way, and...

Oh right, no magic wands. Sorry.

@AlexT: I'm still giggling about the handwave farming in Australia. Ummm, let's see, they're in trouble after a few hundred years, and you're calling that a system worth spending gigabucks building? And you don't want to deal with geologic issues on the blithe assumption that geological timescales doesn't intersect with human timescales in rather painful and spectacular ways? I see.

That, and I'm quite interested in how the solar shielding for Venus will stay in place for hundreds of years. That's a neat trick too. Thing is, if I could build structures like that, I'd rather terraform the Moon. It's a lot closer, for when things break down. Just need a really, big shiny, attractive tent. The ultimate big-top, you might even say.

370:

Ouch! However I am only trying to box in your arguments or paint you into a corner. Ultimately, if you do decide to write a generation ship story, it will be your job to develop the plausible background that is consistent. Being a gadfly to that process is infinitely easier.

371:

"I'm still giggling about the handwave farming in Australia. Ummm, let's see, they're in trouble after a few hundred years, and you're calling that a system worth spending gigabucks building? And you don't want to deal with geologic issues on the blithe assumption that geological timescales doesn't intersect with human timescales in rather painful and spectacular ways? I see."

This was in response to my replying this this comment of yours about Australia:

"stuff tends to get bound where it's unavailable to the biosphere, meaning productivity goes down and the biosphere slowly grinds to a halt. Australia is a great example of this in action today."

I think I misinterpreted your comment. I see now you meant recent European farming in Australia, rather than some slow grinding down of the biosphere over at least tens of millenia, if not much, much longer. Cultures have done somewhat better elsewhere, so I hardly think the Australian experience counts as a support for required geochemical recycling. Venus might have soils that become lateritic, which is not an argument for saying that they cannot support biota.

To reiterate, I think of space colonies long before terraforming Venus, but that doesn't mean that terraforming some part of Venus requires magical technology, just plausible technology on a large scale.

"...interested in how the solar shielding for Venus will stay in place for hundreds of years. That's a neat trick too."

Is it really? In Paradise Regained, Johnson and Matloff discuss just such an option for mitigating global warming on earth using parasols at L1. (ch 14). They call each shade in the required fleet, a "Dyson Dot". What would be different for Venus? Or are you saying they are full of it?


372:

I was thinking that the whole liquifying the surface thing could be fun, when tied in with a bunch of deep boreholes to see what heat you could release more quickly for whatever purposes you like.

373:

Previous post was of course before being reminded of how much thermal energy is stored in Venus's crust...
If someone can work out an easy way of converting energy and transporting it off planet things could get more interesting, but I think that falls under the handwaving tech part.

374:

The problem is the heat sink to maintain the heat differential to do work. The insolation at Venus would be nice for solar PV or solar thermal power though. although the suggested Mercury location would be much better, and you can build those on the surface with
local materials.

Venus is the proverbial hell hole and far less attractive for colonization than any number of other bodies in the solar system.

375:
I just don't see a future in which a fairly static process of building colonies that slowly migrate outwards is likely. Even our 400y future may be a lot more surprising to us, than our civilization could have been envisioned by Shakespeare.

But that's exactly what's happened in several cases. Consider the Polynesian settlement of the Pacific Islands, which took something like 1,000-1,200 years. It was characterized by long jumps from island chain to island chain, followed by colonization of the individual islands of the new chain. I think a lot of our discussion of this sort of migration is hindered by our feeling that there has to be reason for the entire civilization to want to make a move, but in fact I suspect that as long as the cost of a small group taking the jump is low enough, exactly that sort of diffusion is what is most likely to happen.

376:

I'm not arguing with you over the migration pattern, but rather that our rapid technological progress will make this sort of migration obsolete. At its simplest, it would be like the Polynesian's inventing aircraft shortly after they set out from Asia, allowing direct flights to Australia or S.America without stopping at the islands in between. Will humans, or rather what will have become of us, really be slow boating the Oort in 4000 years, let alone 40,000, or doing something unimaginably different?

I would be quite disappointed if I thought that our space colony technology in that future was uprated O'Neill's. It might satisfy the "what can be plausibly done with reasonably extrapolated technology", but that is surely going to be a massive failure of imagination in that actual future.

377:

Imagine Polynesians speculating about the future. They might imagine bigger canoes, perhaps with more efficient sails carrying them faster and more efficiently across the oceans. Perhaps the canoes would be big enough for gardens and livestock that could be farmed on longer voyages. Perhaps they would be so big that they would never land, but people would live and fish from them all their lives, never settling on land.

Life in the C21st, lest than 4000 years after starting and 1000 years after the end of the Polynesian expansion, doesn't even remotely look like that. Ships are largely cargo carriers now, with some cruise ships. Small vessels the size of Polynesian outrigger canoes are largely pleasure craft. Most long distance travel is by aircraft, and the purpose is primarily tourism. Propulsion uses engines not wind.

And that time scale includes just 250 years since the start of the industrial revolution. In just 100 years our way of living has vastly changed, as has the technology at our disposal. I don't see those changes slowing down in the future, quite the reverse.


378:

If we already have the engineering required to build the kind of Solar Shades a Venus project is going to need, why not go all-out and equip the planet with giant radiator fins to help with that cooling? (Or combine the two, and make them giant umbrellas? Reflective coating on the dayside, radiative black coating on the nightside.

(They work even better during the part of the project where you want to shed atmosphere, since you can chimney the air up through them and shed even more heat than radiative cooling alone will get you.)

379:

"I've never understood how this meme of Fusion - In Space! got its hooks so deeply embedded into the science fiction/space community [....] The background assumption seemed to be that this was some sort of cheap and easy tabletop fusion device with negligible radiation worries . . . unlike the real deal :-("

The H-B11 fusion drive which I posted about earlier is 99.9% aneutronic, and it's the same design for which href="http://nextbigfuture.com/2010/07/nuclear-fusion-comonay-trialpha-energy.html">Tri-Alpha has gotten at least $50M in private funding to develop over the past 4 years. It has a shot. If not, then breeder / Thorium reactors are known to work.

380:

Looking at the Wikipedia article on Venus, it appears that Icarus has increased the integrated albedo estimate from 0.76 to 0.9. The original measurements of 0.8 were shaded down to 0.76 under the assumption that Venus was in thermal equilibrium, rather than radiating heat from internal sources. (Otherwise it might appear to further support Veilokovsky, who had already been uniquely right about the temperature of Venus, aside from one guy who thought all the water in the atmosphere would create a greenhouse effect. Not that I think Veilokovsky was right - but he sure has made an awful lot of lucky guesses. See R.A.W. in "The New Inquisition" for more gadfly radical Null-A disquisition on this by the Chief Head of the Committee for Surrealist Investigation of Claims of the Normal (CSICON), wherein he gives Sagan what for, with credit-card interest.)

If the new albedo figure is right, Venus is producing several orders of magnitude more internal heat than Earth.

381:

Is there any chance we could get all the generation ship posts under one link in the Specials sidebar? I know it's extra work, but they've provided excellent discussion and a lot of good ideas, and I think they deserve their own section where we can chart the growth of the concept.

382:

I agree that adding magic wands to the mix changes the range of potential solutions to the interstellar travel problem, but I don't know that it makes it less likely that people will settle the outer reaches of all the systems they can get to. And if they do, then they'll probably keep going out as long as they can get energy, building materials, and volatiles to live on.

William Barton wrote a novel around these ideas, based on a few big-ass magic wands (extraction of energy from the false vacuum, reactionless propulsion up to .25c with accelerations of thousands or millions of g's, human-level AI, effective immortality, usw). It's worth a read: "When We Were Human".

383:
I would be quite disappointed if I thought that our space colony technology in that future was uprated O'Neill's.

Surely your own disappointment is no barrier to this being a plausible scenario?

It's good to keep in mind that the whole idea of continuous (even exponential) expansion of technology is a SF meme, which is quite possibly wrong. In the very long term, it is almost certainly wrong: we will experience lulls in technological progress, regressions, most likely collapses, and at some point our technologies may plateau permanently. And this is all assuming we don't die out.

Given that, it certainly seems plausible to me that in 4,000 or 40,000 years, our technology won't be so radically different than it is today. You can imagine us having far more data sitting around in archives -- the results of drug experiments, genetics tests, and so forth -- with which to understand our situation, but with fundamentally similar materials and computer technologies that stagnated just a few decades or a century or two from where we are now.

The whole idea of exponential expansion and singularities could just be wrong. Maybe human technology will expand rapidly until we can build O'Neill structures, and then slow down and change ever so slowly for ten thousand years, experience a brief spurt of invention in the Kuiper belt, then pull back due to long term economic retraction and general poverty, before recovering and seeing another dozen millennia of slow progress.

I don't see why we have any reason to believe that a future that seems stuck one hundred years ahead of us is somehow implausible, but one where we're uploaded into computronium and spam the stars with robot foundries is perfectly sensible.

384:

EH @ 380
I call whatever the SF-equivalent of Godwins' Law is ...:
"Not that I think Veilokovsky was right - but he sure has made an awful lot of lucky guesses."

Oh come ON! Immanuel Velikovsky?
On the command -one, two, three Eyeballs ROTATE!

In the well known phrase: "You cannot be serious?"

385:

That should be Cosmic Trigger III, not The New Inquisition. Here's a bit (scroll to "The Astronomer who Abolished Gravity").

386:

Polywell fusion has some possibility of success-- the people seem serious and as yet there doesn't seem to be anything that makes it obviously impossible. (Especially not the fusion part, since the Farnsworth fusor the polywell is evolved from produces fusion-- albeit not anywhere near break even)
But even if we get fusion, I myself have very low hopes for long range interstellar exploration. The resources, the effort and most especially the likely length of time you'd have to keep an organization together to make it work all run up against a far more solid barrier than fusion-- human nature.

387:

You mention "mineral riches"

I find myself wondering just how concentrated minerals might become in the micro-gravity environments you're suggesting. Here we are, at the bottom of a gravity well, with a few billion years of heat and pressure and assorted chemistry working on the planetary mass, so that, in a few places, there are workable concentrations of particular rare elements.

How many tonnes of Oort cloud do we need to process to get the lithium for one rechargeable battery?

And, silly idea, maybe a part of the answer to the Fermi Paradox is that all that wonderful mineral wealth we think we see is the worked-out mine tailings from a past civilisation.

388:

Then the necessary precondition for interstellar colonization is a radical change in human nature. QED. What's so hard about this?

(The libertarians will hate it, though.)

389:

>You didn't like the idea of sending out re-supply ships first and sending the generation ship second? You make it sound like an impossible task to snag a resupply pod along the way, whereas I see it entirely feasible if one applies a small amount of imagination...on a small scale think Space shuttle - robot arm

OK, so just to be clear:
if you send the supply pods out at the same speed as the generation ship, it'll never catch them;
if it catches up with them, it'll (by definition) be going considerably faster than they are;
the process of catching and bringing aboard something with a relative velocity of (say) 1 km/s is not a simple one;
slowing the ship down so that it can bring supply pods aboard would be incredibly expensive;
giving the pods little boosters so they can accelerate to match velocity with the ship is exactly equivalent in delta-v requirements to launching them at the same time and at the same speed as the ship, or indeed just putting the pods aboard the ship before launch.

390:

Supply ships, or staging?

The concepts have enough similarity to be worth a look. But getting the rendezvous and cargo transfer has a cost in reaction mass and energy. The two craft have to be in the same place at the same speed, and space is big, really big.

It maybe makes sense to launch two ships at the same time, one of them intended never to stop, and carrying the reaction mass the other needs to stop. On the other hand, the failure mode on that scheme is pretty obvious. But we do seem to be assuming that we have to stop everything we start off. Maybe we're using some sort of fusion reactor for the propulsion power: why not jettison it after the boost phase, along with all the empty reaction mass tanks. Don't worry about what the neutrons have done to the structures. It doesn't need that big a kick for it soon to be a long way away.

Oh, re-cycling the materials? Well, maybe, but that neutron flux will make the reactor itself pretty hard to handle: radiation and the isotopes will be changing the quality of the structural materials.

And remember, we're not near enough to a sun to have cheap energy. You might be able to do zone-refining with some big mirrors, here around this planet, but there?

You might end up with a string of reactors, Propulsion-A, several for coast-phase "Hotel" power, and Propulsion-B, with most of the mass jettisoned. And once you get down to interplanetary speeds, you go back to solar energy.

(I think I shall go read "Surface Tension")

391:

EH @ 380, 385

I think we have a loonie &/or a troll in the house.
Seriously, Velikovsky was a MEDIC.
His strange interpreteation of ancient myths, whilst ignoring the practicalities of celestial mechanics would be hilarious, if it wasn't for some people taking them seriously.
Mind you, some people believe in invisible sky fairies .....

392:

>I find myself wondering just how concentrated minerals >might become in the micro-gravity environments you're >suggesting.

The only analogue material for Oort cloud matter are possibly cometary dust and (big) maybe some primitive
meteorite (types 1and 2). Their chemistry is roughly
Solar (except H and He), so they are (chemically) basically unfractionated from the bulk solar system.

So no substantial concentrations like e.g. on Earth or differentiated asteroids. So for mining the belt is better (although Ceres is probably also quite primitive).

>How many tonnes of Oort cloud do we need to process to >get the lithium for one rechargeable battery?

Solar system abundance is about 1.5 ppb, so probably quite a lot.

393:

It maybe makes sense to launch two ships at the same time, one of them intended never to stop, and carrying the reaction mass the other needs to stop.

Well, putting aside the pickup issue (how do you catch something that you're whizzing past at 1 km/s?), if you catch it, it'll slow you down. Conservation of momentum. So there really is no obvious delta-v advantage to launching separately rather than launching both together.

394:

Ah, what catching? They're launched at the same time.

395:

[I'm presuming you're replying to me @353.]

Yes, sorry. I was making the reply when the server decided my session had timed out. And by the time I'd gone through the login again, the 'Replying to' had dropped.

396:

The problem is - if we can build a spaceship people can live indefinitely on, then we just lost the reason for interstellar travel. Why colonize anything, if you can just live in space?

"Don`t put all eggs in one basket" is fine and good, but we just learned to make our own baskets. Disperse them around the solar system and you are more or less invulnerable (even gamma-ray bursts can`t harm you now, because your atmosphere is inside the hull).

And if you want a pretty wild-looking biosphere, well, build a large enough ship and you can have it right on board, with forests, lakes and all.

397:

Surely your own disappointment is no barrier to this being a plausible scenario?

I do - and stop calling me Shirley!

398:

Velikovsky was a crank; anyone taking him seriously is well off the beaten path and into the swamp.

Robert Anton Wilson was intermittently entertaining but made no pretence to have the answer to Life, the Universe, and Everything: he just collected cranks, kooks, and conspiracy theorists for teh lulz.

399:

I think you're pretty much correct; the only point I'd like to add is that solar systems come with conveniently pre-fractionated piles of elements, sorted by diffusion and gravity under light pressure as the star they orbit forms and ignites -- and they're in very close proximity compared to the Oort cloud. So I suspect interstellar migratory space colonies briefly venturing in close to those dangerous high-energy radiators to pick up supplies (and maybe drop off some adventurers if there's a suitable location for building new migratory colonies) is the model to go with. If we are long-term viable in space.

400:

Whenever I think about space travel realistically and not as an embodiment of all the SF novels I read, I am convinced that long term colonization/exploration on either planetary or interstellar scales will require a new round of speciation. Either genetic adaptations to suit us to environments and/or time scales OR some kind of meld with machines, virtual or cyborg-ian OR simply passing the baton on to machine intelligences. Now how and why civilizations with those capabilities will want to do space exploration is a fun area to explore.

On the short/medium term, we as our current species could probably have some fun setting up bases on Mercury or even Mars or pick your favorite Solar System Object here. But in the long term those projects will almost certainly run their course or fail. To KEEP Mars terraformed would require such long time scales that speciation would almost have to be factored into the equation from the start; so why bother making a new Earth there or anywhere.

On the other hand, the more I hear about what we could do at or around Mercury, the more I think it has got to be at least a pleasant diversion for the new millennium, assuming we can maintain a high surplus culture into the future.

401:

you seem to be a couple of enhancements away from reinventing the multi-stage rocket.

402:

>>>Now how and why civilizations with those capabilities will want to do space exploration is a fun area to explore.

Well, as long as our descendants still have curiosity, they will want to explore something. 8-)

403:

The one possibility that makes some sense to me in this context would be to launch (most of) the fuel that the ship will need to slow down earlier and slower. Arrange things so that the ship catches up at the point where you want to start braking anyway, and the loss of speed as you match velocities is not a problem.

Of course, this does require you to be planning things very definitely a long time in advance; to represent a worthwhile saving (from not accelerating all that fuel up to travel speed) you're probably looking at boosting the supply vessel out a hundred years earlier than the main generation ship.

Even then, there are disadvantages, though - you lose a lot of flexibility. You can't change your destination (or even your route) once the fuel ship has gone out without sending a new one. You can send the generation ship out early, but only at the cost of extending its time in flight - and you can't send it more than a little later than planned, or it'll catch up with its fuel too late to do any good. (Oh, and there's the possibility of your ice block getting knocked off course by a collision in deep space, in which case your colony ship no longer has the capability to slow down. Unfortunate, that....)

404:

I rather think that, by the time you've slowed the colony ship enough to not convert the self-loading cargoes into strawberry jam as it makes its rendezvous with the "braking fuel" you'll find that you might as well have launched all the fuel with the colony ship anyway, unless you have a punning clan for making the braking fuel part of the structure of its "ship".

405:

Aren't they indeed?

It's not a bad idea if generalised out to a small fleet. You set off with a bunch of ships you intend to go all the way, and a few I shall call tenders.

A tender accelerates with the rest of the fleet, but instead of being designed for habitat, all it contains is fuel and other consumables, which it feeds out to the rest of the fleet, keeping their tanks/stores topped off as long as possible. When you exhaust the first tender, you abandon it - no point in accelerating its structure any longer - and start on the second tender.

Since slowing down for the destination is also acceleration - merely in the opposite direction - there's nothing saying you need to have finish the last tender before beginning that slowing down process.

I'd posit a fleet as being a bit more resilient than a single ship, in that you need a bigger disaster to take out a fleet.

406:

That would depend on the mean time between catastrophic failure for a single unit. One thousand years would in fact be acceptable from a species survival point of view, given a sufficient number of units, but 100 might be too short.

Then we're on to the 'do you really want to live there'. 1000 years would imply that someone living to 100 inside such a colony has a 1 in 10 ish chance of dying by sudden failure (meteor strike, runaway ecosystem failure etc). It's probably lower than cancer, so it ought to be acceptable, but would it be?

407:

That's an unacceptably high hull loss rate for a habitat. Because what you're talking about is really the probability of your entire nation of residence being wiped out by a catastrophe, including not only yourself but your family, friends, and almost everyone you know.

(On the other hand, that's a hypothetical 1 in a 1000 year rate for catastrophic destruction of the entire hull. If it could be reduced to, say, 1 in 10^6 for catastrophic destruction and one in 10^3 for serious but repairable damage with some fatalities, that's a very different proposition.)

408:

aahh - that's neat. To spell it out a bit more to be sure i'm understanding:

You start a long time before your payload is ready to depart by launching a series of tankers that will accelerate to different speeds and then drift towards the destination. You send the slowest first according to some carefully planned schedule (it isn't quite right, but timing them all to cruise past the destination at the same time has about the right flavour).

Then you launch your payload with just enough fuel to accelerate to its desired cruise speed and then slow to match speed with the fastest tanker. You time its launch so that it rendezvous with the first tanker, which supplies it with just enough fuel to match speeds with the second tanker, and so on.

What you save is the energy cost of accelerating all the deceleration fuel to full payload cruise speed, i.e. shorter payload journey time for a given energy budget. What it costs you is project start to payload arrival time is longer than the slowest tanker trip time, and you have to achieve a series of horribly delicate deep space rendezvous or your payload goes flying past the destination with no fuel to slow down.

409:

Those ships aren`t supposed to travel to other stars very fast, so they can be built very safe, with thick armor and lots of redundancy. Also, assuming the failure is not instantaneous, you can just leave for another habitat or call for help.

410:

I was thinking of somewhere between "town" and "city" - Bairnsdale to Leicester. I suppose a large one could well be more somewhere to live than a mobile city that went to where the business was.

411:

What you save is the energy cost of accelerating all the deceleration fuel to full payload cruise speed, i.e. shorter payload journey time for a given energy budget.

So if I understand it, you launch a series of pods that accelerate up to (say) 60, 70, 80 and 90. Then you launch your payload, which accelerates to 100 and cruises most of the way there; then it decelerates to 90, RVs with the pod going at 90, fuels up, decelerates a bit more, RVs with the pod going at 80, and so on.

My gut instinct is that you would still have the same total energy budget as if you just launched all the fuel on the payload, but I haven't run the numbers. I don't think the laws of dynamics are that easy to get round.

412:

Here's a random whimsical alternative:

Recent calculations have demonstrated that a Bussard Ramjet can't scavenge enough fuel from the interstellar medium to accelerate efficiently -- in fact, they make rather good parachutes.

But what if we enrich the interstellar medium in the course of our proposed starship? Send out a stream of fuel cans, then have them spray their contents out along a narrow path, enriching the corridor the ramscoop will fly down by a couple of orders of magnitude?

(I have not attempted to tackle this numerically; it's way above my pay grade. Is it plausible, though? It won't cut the total time to bridge the interstellar gap, but it may cut the time during which the high-value payload of canned monkeys is in transit.)

413:

No, he's right, there's a considerable energetic advantage, every kilogram of decelleration fuel that comes along on the main ship is a kilogram of fuel that needs to be accelerated to the high speed. It would require a very long planning horizon, and the ability to stick to deadlines on that planning horizon.

414:

Let me try some alternate scenarios that might make this settlement of Oort bodies less likely.

1. Unlike pacific islands, Oort cloud bodies are not fixed in space and time. They could be seen less as a place and more as a resource which could be mined and moved to other locations. Thus rather than settlements, we see mining platforms, and the material is sent to the inner system, perhaps to support a Dyson Sphere.
(Repeat for each target star).

2. We get truly "magic" interstellar travel. Say beaming objects to destinations at C or FTL speeds. Now even if suitable worlds are 1 in a billion, there are hundreds to go to in the galaxy alone. The universe would offer trillions of worlds. Maybe you would want your private snowball, but why not a whole shiny new world?

3. Humans become "post-human" (whatever that means) and do not live in the material world any more, obviating the need for Oort resources in favor of something else.

When you are talking about time scales of 10's of thousands of years, for a species that uses rapidly proliferating technology, it seems unlikely that the migration period looks even remotely as static in form as the Polynesian cultures over their possible 4000 years of trans-Pacific expansion. (They started out as hunters and agriculturists, using slow, ocean going vessels, and ended the expansion that way).

415:

Recent calculations have demonstrated that a Bussard Ramjet can't scavenge enough fuel from the interstellar medium to accelerate efficiently -- in fact, they make rather good parachutes.

Which gives me an idea; use "conventional" means to accelerate, and when we want to brake, then we deploy the Bussard collector but forget about firing the collected stuff out the back fast, just let it leak. Call it the "Bussard - O'Neill* rambrake"!

* That's my real surname (the O'Neill part), and if this is an original thought, I claim my right to name the device!

416:

"Surely your own disappointment is no barrier to this being a plausible scenario?"

and:

"It's good to keep in mind that the whole idea of continuous (even exponential) expansion of technology is a SF meme"

It is plausible. It is not an SF meme. Our historical experience does not indicate any technological limits. Quite the reverse. Every time someone suggests that we have reached the end of some science or technology, we get an unexpected development that changes everything.

"Given that, it certainly seems plausible to me that in 4,000 or 40,000 years, our technology won't be so radically different than it is today. You can imagine us having far more data sitting around in archives -- the results of drug experiments, genetics tests, and so forth -- with which to understand our situation, but with fundamentally similar materials and computer technologies that stagnated just a few decades or a century or two from where we are now."

Really? Despite all the evidence to the contrary that we use new technology, you think that we will just "stop"? That biotechnology will just be peripheral rather than transformative?

"The whole idea of exponential expansion and singularities could just be wrong. Maybe human technology will expand rapidly until we can build O'Neill structures, and then slow down and change ever so slowly for ten thousand years, experience a brief spurt of invention in the Kuiper belt, then pull back due to long term economic retraction and general poverty, before recovering and seeing another dozen millennia of slow progress."

In which case it is just as likely not to get to O'Neill colony stage. And if we do, why should they be planted where the resources are, rather than inner system where the energy is? More likely our technologies will lead us off in new directions, possibly ones we cannot even imagine today.

417:

I don't know if it's plausible, but people have thought about it before. It's even in the wikipedia article.

418:

Which gives me an idea; use "conventional" means to accelerate, and when we want to brake, then we deploy the Bussard collector but forget about firing the collected stuff out the back fast, just let it leak. Call it the "Bussard - O'Neill* rambrake"!

Also known as the Andrews-Zubrin magnetic sail, I think.

http://en.wikipedia.org/wiki/Magnetic_sail

Sorry... good idea though. You might even be able to do something clever with the nano-tesla background magnetic field of the galaxy.

419:

OK then - as I say, I haven't run the numbers. The "no free lunch" payoff that I suspect is there may be the longer total mission time. (From first fuel pod launch to arrival.)

420:

@ 412:

But what if we enrich the interstellar medium in the course of our proposed starship? Send out a stream of fuel cans, then have them spray their contents out along a narrow path, enriching the corridor the ramscoop will fly down by a couple of orders of magnitude?

(I have not attempted to tackle this numerically; it's way above my pay grade. Is it plausible, though? It won't cut the total time to bridge the interstellar gap, but it may cut the time during which the high-value payload of canned monkeys is in transit.)

We've already done this one before too. Start at about comment number 218:

A pellet-stream concept for interstellar propulsion is described. Small pellets are accelerated in the solar system and accurately guided to an interstellar probe where they are intercepted and transfer momentum. This propulsion system appears to offer orders-of-magnitude improvements in terms of engineering simplicity and power requirements over any other known feasible system for transport over interstellar distance in a time comparable to a human lifespan.

Notice that you don't need anything material to catch the pellet or capsule or fuel pod or whatever; a current carrying loop is enough to interact with the intercepted mass. That's a good deal, because catchers like this (unlike, say, solar sails) scale roughly linearly with size instead of going with the square. At the distances you're talking about, you're going to be taking full advantage of this fact.

421:

Interesting that the generation fleet seems to keep coming up independently.

422:

Some of the obstacles may be correctable in the second generation. For example, even if we end up with an imperfect exo-womb that causes serious (but not lethal on a 25-year horizon) defects and developmental problems (that do not disable puberty), we may not really have to care as long as our robots can keep them alive and they're capable of breeding themselves (with or without robot help), since their wombs will be perfectly fine (or at the very least a whole lot closer to standard) and we don't have Lamarkean evolution going on.

Likewise, we don't necessarily have to preserve human culture, as long as a sufficient critical mass of humans can socialize themselves into something and the n-th generation of that culture can be counted on to eventually discover archaeology.

This plan does involve coldbloodedly condemning our zero generation of colonists to an awfully inhumane condition of being. But it could work without having to wave wands of vat-growth and creche-raising...

423:

SoV beat me to it, and in fact, the Orion's Arm gang has been using the pellet stream as the basis for their Beamrider network for quite a few years now.

A beamrider, by the way, looks like a backwards Bussard Ramjet. It is designed to catch fuel shot at it (small, self-guided AI missiles shot out by the launchers based on moons or planets), get some delta V by slowing and vaporizing the fuel, then collect the atoms from the vaporized fuel and use it to build supplies.

Ships on the beamrider network don't slow down much, either. They just load and unload passengers and freight to long-range lighters that match their speed, transfer cargo, then turn around and return to their home systems.

Considering that the shielding needed to survive interstellar space looks a lot like the shielding needed to catch fuel pellets, this might actually be workable. Of course, the infrastructure is enormous, but if it falls apart, a beamrider ship can potentially reconfigure to a mag sail drag chute, to slow down and settle in a planetary system.

424:

@ 423:

Ships on the beamrider network don't slow down much, either. They just load and unload passengers and freight to long-range lighters that match their speed, transfer cargo, then turn around and return to their home systems.

If you use the current-carrying loops to catch the incoming stuff, you can also use them in a deceleration mode as well - either to accelerate the propellant even faster in the same direction it's already going, or as a magnetic brake against the interstellar medium, like the Bussard Ramjet is not supposed to :-)

I'll leave it to the other commenters and an elementary application of trigonometry to figure out what sort of aiming errors can be tolerated by this system.

425:

Interesting question that no one's addressed:

One of the best reasons for settling a planet or moon with active plate tectonics (and planets with a biosphere) is that active biogeochemistry concentrates quite a few elements in usefully mineable deposits.

Assuming that one would want to visit another star system, the interesting question is whether it's more useful to land on a planet to mine concentrated deposits, or to work on asteroids and concentrate the same atoms from much more homogeneous asteroids, comets, and moons. I suspect the answer is "it depends," but given that things like mag-sails appear to demand rare earth elements that get concentrated in planetary crusts.

426:

Yes, the mission time from initial planning (or first launch) to arrival is going to be considerably longer (and, as Tim and I both noted, your timing gets very rigid, which has its own drawbacks). The payoff is that you can either reduce your energy budget quite considerably or you can move the valuable payload (the canned monkeys) somewhat faster for the same energy budget. Or, of course, you can send more apes and equipment for the same energy budget.

That last, now I think about it, ties in rather well with the 'generation fleet' concept. If you're sending a group of very large ships instead of one huge one, the reduced fuel cost per tonne of ship-mass allows you to improve your fleet's chance of arrival by building more ships than otherwise. Extra ships means more spares, better chances of being able to cobble repairs to otherwise-critical damage, and lower chances of losing the whole lot to (say) an unexpected .5c meteoroid.

427:

What cargo can possibly be worth transporting from one solar system to another? I can`t imagine almost anything that won`t be cheaper to produce locally. The only stuff worth transporting would be humans and information. And maybe alien organisms, if we find any.

428:

I am serious - I don't think Velikovsky was right. He did make some predictions that seemed unlikely at the time but were later verified - temperature of Venus, radio waves from Jupiter, existence of Earth's magnetosphere, perhaps others since Princeton Physics Prof. Valentine Bargmann and Columbia University astronomer Lloyd Motz listed these in 1962. Other claims seem as unlikely as ever.

The points are:
1.)being wrong in general doesn't make one wrong in detail;
2.)neither making correct predictions nor having incorrect arguments (such as some of Sagans) directed against one means that one's whole argument is correct;
3.)grappling with actual evidence improves thinking, particularly flexibility, while ignoring evidence to fit hypotheses leads to mental rigidity and sterility (and a high likelihood of being wrong); 3.)a. R.A.W's main point: to deal with evidence in the real world requires thinking in constantly shifting maybes rather than eternal certainties.

This "maybe" way of thinking leads to more creative possibilities, while taking the fundamentalist view that "we know everything important in science already" leads to dull thoughts that may later look just as silly (but far less entertaining) as some of the things the Forteans consider.

429:

Biographical FYI -

If you want to get seriously into this, you need to own or have read (off the top of my head) -

* Finney and Jones, "Interstellar Migration and the Human Experience"
* Matloff, "Deep space probes"
* O'Neill, "The High Frontier"
* "Space Resources and Space Settlements", NASA SP-428
* Larson and Prancke, "Human Spaceflight Mission Analysis and Design"
* Eckhart, "Spaceflight Life Support and Biospherics"

...and probably:
* Larson and Wertz, "Space mission analysis and design"

430:

"Velikovsky was a crank"

"... Velikovsky is neither crank nor charlatan — although to state my opinion and to quote one of my colleagues, he is at least gloriously wrong."

-Stephen Jay Gould, "Velikovsky in Collision", Natural History, March 1975; Reprinted in Ever Since Darwin: Reflections in Natural History, New York: W. W. Norton & Company, 1977, pp. 153-159

Again, Velikovsky was wrong in general, there are many valid criticisms of most of his arguments, but he was trying to come up with natural explanations for myths. Sagan on the other hand, while an excellent popularizer, seemed at times to be waging a holy war against heresy and though his tactics were clearly effective, as seen from the persistence of hyperbolic reactions to the mere idea that V. could have been right about anything, even by accident - Sagan's tactics towards V. were likely a greater danger to science than V.'s mere wrongness.

Anyway, back on topic: Venus seems to be a lot brighter than we used to think. With an albedo of 0.9, sunshades aren't going to do much.

431:

Depends where you're starting from and comparing yourself to. "Stuck in a terraformed cylinder 100 km long" may be a bit restrictive if your alternative is "living the good life in California's beautiful San Fernando Valley" but it might be a bit more appealling if the alternative is "dying in a refugee camp on the Thai-Burmese border".

If a world has refugee camp on the Thai-Burmese border (or some equivalent thereof), how can it possibly afford to build generation ships?

And if the world by and large is wealthy enough to build generation ships, yet has pockets comparable to said refugee camps, it implies huge levels of inequality, hence social tensions, hence refugee camp is the last place where wealthy population would recruit crewmen for what can be easily turned into planet-destroying weapon.

432:

What cargo can possibly be worth transporting from one solar system to another?

A biosphere. Loosely, not just an organism (canned monkeys) but an interdependent set of organisms that coevolved and need each other in order to survive. You might be able to build a monkey from scratch, but building the monkey in parallel with the entire rain forest it depends on for shelter and food is a much, much harder problem. It's probably easier to send one that is already up and running than to try a cold boot on a system that was never designed to survive shutdown.

433:

I do take your point on not being too skeptical but consider that it is possible to have so open a mind that all kinds of crap flows in, un-filtered, with the information stream.

Have a look at 'Shotgun Effect " which is, in my own 'umble opinion the futuristic charlatans friend so that .. ' He got That Right can the rest of the wacky theories be entirely wrong ? ' ...says the Innocent.


" The act of turning in a whole bunch of applications to different areas of employment in hope that at least one of them employs you.

The "shotgun effect" could mean anything involving multiple usage of something until something happens. It is similar to how a shotgun shoots : it fires a spread of buckshot, so if you're shooting a buckshot round from a distance, you'd better hope at least ONE of the pellets hit the target. "

http://www.urbandictionary.com/define.php?term=shotgun%20effect

Velikovsky reminds me irresistibly of Erich Anton Paul von Däniken who was wildly popular once upon a time with his work even being published in the British popular newspapers way back in the time of my youth.

http://en.wikipedia.org/wiki/Erich_von_D%C3%A4niken


Were we ever so Innocent ..well, I wasn't, and nor was,say .. Tuesday Lobsang Rampa ..


"Rampa is the spirit of a dead Tibetan lama (monk) that allegedly took over the body of Cyril Hoskin (1910-1981), a British-born plumber living in Ireland, in the mid-1950s. Hoskin submitted a manuscript to the publishing firm of Secker & Warburg entitled The Third Eye and allegedly authored by Lama Lobsang Rampa. "


http://www.skepdic.com/rampa.html

Those were the days.

434:

So the rich world cannot offer places to those of the poor world (in exchange for some benefit (current or future)? A few centuries ago we did this with the slave trade. Why cannot we do it now with a fair transaction?

435:

You are correct (although some radical biotechnology developments can challenge that), but I assume that a biosphere only needs to be transported once, along with the colonists. It won`t generate interstellar traffic.

436:

"Venus seems to be a lot brighter than we used to think. With an albedo of 0.9, sunshades aren't going to do much."

Only if you leave the atmosphere intact. But strip it away and shield Venus from the sun and the surface will receive no sunlight. Of course the surface will take a long time to cool via radiation, but it will cool to equilibrium eventually.

Consider that the moon gets very cold during it's night. Thought experiment: Shade an atmosphereless Venus, levitate the top meter of rock to isolate it from conduction from the rocks below, that surface would get quite cool, pretty quickly.

437:

Unique -as a One Off - or thematically Original, Art work perhaps? Basically something new that is sold to the Creature that Has Everything on the basis that no-one else can have it or something so OLD and rare that there will never be another.


http://en.wikipedia.org/wiki/List_of_most_expensive_paintings

438:

if we can shade Venus, why not shade Mercury as well? It will be easier to build an atmosphere there, than to get rid of venusian atmosphere. And surface temperature is much better.

439:

Granting that we have that kind of technology One Fine Day - or Eon - then why not simply dissolve both Venus and Mercury into a kind of Interplanetary cake mix and then use the Mix to make an Interplanetary Fruit Cake or Plum - Plumb - Pudding of Super Colossal Size?

Sorry but my grasp upon Mathematics is disgracefully limited and the thought of a Super Colossal Plum Pudding is irresistible.

440:

Indeed, Mercury is a better place to go, as heteromeles suggested earlier in this thread.

Since it is inactive, there isn't the issue of hot subsurface rocks transferring a lot of heat to the surface, so it should be easier to cool, and no atmosphere stripping needs to be done.
Surface gravity is about the same as Mars, so that is nice too.

IIRC, John Varley had a story based on Mercury, with humans using personal force fields and implanted oxygen sources to walk on it's surface.

441:

A. Rich world may honestly think it is a fair transaction and perhaps even most of poor world agrees, but at least a few in the poor world will think they are still being exploited. Or are just owed more. If NOBODY thinks that, then either they are not really poor (and your original suggestion is moot), or human nature has undergone some drastic readjustment.

B. It is rather difficult to ensure your starship crew does not contain some of these "few".

C. Any ship capable of traveling between stars is by definition a weapon.

Still want to recruit your colonists from Thai-Burmese refugee camp?

442:

I like the interstellar space-fountain idea, but I wonder how one keeps the solar-system end in place rather than falling towards the sun. Perhaps use two starships going in nearly opposite directions, with the stream bent a little as it passes through the solar gravity well?

The required precision of aiming needs a bit of working out, too - perhaps quadrupole magnets or charged plates to focus and perhaps further accelerate the stream at intervals along the way would be needed. Rather than dropping them behind each ship, perhaps they could follow, riding the rails.

How fast and how dense would the pellet streams be and what does that imply for the energy and mass requirements? Well at 0.33c spaced 10 km apart, with 1mg pellets, the frequency would be 10 kHz, and the mass would be only ~9.3E6kg/ light-year, with a throughput of ~4.5E14W, most of which would be captured from the incoming stream at the ship and applied to the outgoing stream. With losses of ~2% each ship would have to produce 9E12W for propulsion. (Or maybe the sun-bound rails could be slower than the outbound rails.)

The power and mass for initially accelerating and extending the streams would likely need to be located in or close to the solar system, and while the net momentum of the center station wouldn't be changed by this, a method to keep the station, well, stationary would be needed - perhaps a series of solar-orbiting stations briefly slowed using tethers or something. Or have enormous power-plants on board the ships, which defeats the purpose.

This whole contraption is basically a relativistic machine-gun. Like the launch-laser concept, one would want some safeguards against repointing it towards inhabited bits of the solar system.

443:

This whole contraption is basically a relativistic machine-gun. Like the launch-laser concept, one would want some safeguards against repointing it towards inhabited bits of the solar system.

Given the low masses of the pellets involved, one could design the system so that the pellets would burn up harmlessly in the upper atmosphere if pointed at Earth.

That would certainly not be an optimal thing to have be cascading in; low earth satellites and any other space structure would be horribly vulnerable. But designing it so that you couldn't kill people on the ground per se sounds entirely feasible.

444:

It's worth shipping anything that is simpler to ship than explain. Thinking can cost money, depending on the economy.

445:

There's a nastier problem with the Bussard Ramjet that's been known for several decades: in order to capture interstellar hydrogen to use as either fuel or reaction mass, the ramscoop has to accelerate the hydrogen atoms, thus losing momentum (in effect increasing the drag of the medium). This effect is similar to the problems of a ramjet travelling in atmosphere at super- or hypersonic speeds. The problems in atmosphere are fixable by (among other things) changing the combustion model for the jet so the supersonic airflow doesn't blow it it out; it's unclear if there is a similar solution for a fusion reaction in a relativistic gas flow. Even if that problem is solved, the reaction mass has to be slowed significantly or it won't transfer enough momentum to the vehicle.

446:

The Jack Horner Project?

447:

Ob-Goons: The International Christmas Pudding.

448:
When you are talking about time scales of 10's of thousands of years, for a species that uses rapidly proliferating technology, it seems unlikely that the migration period looks even remotely as static in form as the Polynesian cultures over their possible 4000 years of trans-Pacific expansion. (They started out as hunters and agriculturists, using slow, ocean going vessels, and ended the expansion that way).

I think you're assuming that travelling in space is a primary goal, so people will use the fastest possible means. I don't agree, at least for most people; I think traveling in space will be primarily a way to find someplace to live; having done so, most people will want to settle down and do something other than travel (except perhaps for the folks who decide they're happing living in their interstellar generation ship, and who just don't bother to stop). If you have enough energy to run a civilization and enough matter to make the food and material possessions you need, and there are enough people for a viable culture within reasonable communication distance (a few light-seconds? anyway close enough for a realtime conversation), what else is going to be important enough that you want to go somewhere else? Particularly if you can still communicate asynchronously with other groups of people, to trade information and entertainment (art, science, sports, politics are all entertainment, especially from a distance).

449:

Mercury is a useful place to colonize for reasons other than available energy and mass: you can use it as an interchange for travel between other parts of the system for a couple of reasons. First, even Hohmann trajectories between Mercury and other places in the system are fairly fast, hyperbolics can be be very much faster especially for trips between points further out, or currently on opposite sides of the sun (slingshots around Mercury need to get close to the planet to get a hard pull from its gravity, but its orbital velocity is the highest of any large body in the solar system, so you can get a fair amount of delta-v out of it). Second, the Mercury-Sun Lagrange Points provide several convenient places to hang momentum transfer tethers (and lots of solar energy to restore the tethers' rotation if you can't conveniently match transfers with opposite vectors).

450:

Aren't you describing a Dyson Sphere constructed of colonies, rather than the same scattered through the Oort? Within 1 AU, energy availability and communication speeds are going to be a lot better. Which isn't to say that people cannot go elsewhere.

But my main issue is whether this living in space colonies, wherever they are, is going to be done. I just think technology will change teh game so much that space colony living will be as obsolete as living in mud huts.

451:

I'll take your word for it, but Mercury's position in the gravity well makes reaching it quite hard (today).
Is it's position an advantage compared to having tethers slingshotting craft around in other parts of the system?

452:

very true, u got the scariest predator the planet has ever seen looking after you

453:
"a. R.A.W's main point: to deal with evidence in the real world requires thinking in constantly shifting maybes rather than eternal certainties."

You might be interested in the work of Paul Feyerabend[1], looking at the history of science, there seems to be no general algorithm to work sucessful. Problem is, with the same logic, you could also say that at times it's necessary to stick to one narrow worldview even if there seem to be reasons that justify a broader approach. One could argue that Feyerabend himself used an approach like that when endorsing eliminative materialism.

Err, if anybody accuses my of quoting the poster child of crackpot theorists to defend crackpot theorist, leading to an 'oh, typical'-shoutout, Ernst Mayr himself voiced some liking for Feyerabend, so I'm not in that bad company, call it argument from authority, call it quoting somebody who was more part of scientific history than me, and then, it may be a biologist meme[2].

BTW, mixing the Velikovsky and Wilson darn, what about Velikovsky being part of some JAM conspiracy to discredit pessimistic guesses about habitats on Venus, thereby negating some antagonism on the way to space exploration; come on, the guy looks like C.G. Jung sometimes, and we all know who Jung really was[3]...

[1] Given the fact I first came about this fella in a SF book, "Observation on the spot", by Lem, it's even kinda on-toppich.

[2] My god are there a lot of us here. Seems we have too much time at our hand...

[3] Fuck, I knew it, there was some AUM in the Club Mate supply at 27C3...

454:

Thinking about it some more, the mass requirements for the pellet stream are so unexpectedly low the solar station could throw the opposing stream into the sun, giving a large part of the thrust needed to hover over a solar point (perhaps far from the sun, with the power beamed in from close solar orbit, or perhaps using an orbital loop for support close to the sun.)

The starship could simply stop the incoming pellet stream rather than returning most of it. The pellets could provide not only momentum, but also the energy provided by decelerating them could directly provide power for ship's systems, uncollimated return at lower Isp of some of the incoming pellet stream for more thrust, and perhaps a bit of additional fuel for the ship, too.

455:

I'd expected that the pellet stream would be stopped, meaning turned to plasma. Using the machine gun analogy (or better yet, the gyrojet analogy), I'm not sure that you could reverse the course of pellets and send them back without destroying them. It's probably just easier to shred them to plasma, and use the plasma for as many things as you can figure out (elemental resources, possibly shielding, fuel for lateral maneuvering) and dump the rest.

Still, I keep thinking about the Black Beauty from the Green Hornet getting propelled forward by its pursuers' machine guns. That this seems to be a reasonably practical propulsion system says a lot about the difficulties of interstellar travel. Still, I guess it beats sleeping over a few pounds of antimatter for a century or two.

456:

I wrote:
Reducing the materials process to grinder + magnet + DMLS is probably roughly the space manufacturing equivalent of magic, and we are probably right about there. Someone needs to try the experiment (sacrifice some meteor fragments as input material for actual tests) but it seems like we're about there right now.

Scentofviolets responded:
!?!?!? Very nice, if true. But on that one I'm afraid I'd have to see some cites before I believe it.

I just proposed doing the experiment to one of the research organizations (SSI) in the space field. Hopefully, citation to follow, though it would probably be a few months even if they go for it. I recall this was vaguely floated at the Space Manufacturing Conference after-hours discussions late last year but I don't know of anyone having kicked off an actual test. So I will.

I haven't got the tensile test rig to measure the resulting parts' basic mechanical properties but they have associated people at universities and in industry who should.

457:
It is plausible. It is not an SF meme. Our historical experience does not indicate any technological limits. Quite the reverse. Every time someone suggests that we have reached the end of some science or technology, we get an unexpected development that changes everything.

Just because it's an SF meme doesn't mean it's not plausible. It just means it's a good idea to step back and re-check your prejudices where that meme is involved.

In that vein, step back and look at your argument: it is not really a valid argument about long term technological progress. Why? Because it's not based on what we know about science or technology. It's based on history and psychology.

That doesn't mean the conclusion is untrue. It just means that this argument doesn't really let us conclude anything about technological progress. It might be true that humans will continue to desire and seek better technologies, but that doesn't mean we'll achieve them.

We're living in a time of rapid technological change, so it seems perfectly plausible to think that this is the way things will always be. But can history or the present really guide us here? We're developing rapidly improving technologies because we want them, sure, but more fundamentally, because they're possible. We can desire and research FTL travel all we want, but we simply aren't going to develop it if the universe doesn't play along.

Look at space travel (the subject of the hour): it hasn't actually changed a whole lot since 1965 or so. Sure, we have some different rockets, and the industry has expanded a bit, but progress has been pretty slow. The biggest improvements we've seen have really just been offshoots of computer technology: more capable robots, smaller and cheaper satellites.

Back in the '60s and '70s, right in the middle of the Apollo program, people certainly had a far more optimistic view of the future of space travel than you're likely to find today. Need I point out that sending a manned mission to Jupiter by 2001 seemed quite plausible to people back then? It's 2011 and we've scaled back our ambitions: building some cheaper throwaway rockets, and perhaps a suborbital joyride or two, seems like great work now.

So why should we expect technology to keep changing at a rapid pace? History just points to ambition (and for most of it, not even that). We need to look at the natural world to see what's likely: if there's something that clearly seems useful and doable, then most likely we'll see change. If not? Well, we might discover something new, but who knows? We might get stuck in a rut too.

458:

Actually, we could send a manned mission to Jupiter in the '70s, and we still can. It is a matter of cost, not technology.

459:

EH @ 428 & 430
Point about (Velikovsky) being correct in some details.
The trouble is that... he was so fundamentally, eyes-rolling wrong and loopy about the generality, the big picture, that, quite reasonably no-one paid any attention to the small stuff.
So he WAS off his head - remember: a stopped clock is correct twice a day.
And, yes, he was a crank.

Archy @ 433
Those days are still with us.
They're called religious leaders, claiming the world for [insert name of preferred big sky fairy here] and his truth, and death to the unbelievers....

@ 441
Erm:
"A wind from a burning woman" & The Kzinti lesson.
Indeed.

460:

You missed one fundamental way space travel has changed since the 1960s: the use of gravitational slingshots, and then of chaotic orbital dynamics, to move spacecraft around with very little energy inputs.

Yes, it's a side-effect of computers, but it's a significant one.

Shorter form: the Grand Tour on the 1970s -- first the Pioneer 11 mission, then the Voyager 1 and 2 missions -- were sequential gravitational slingshots, enabled by the outer planets lining up just so. (It was a cut-down version of the original Grand Tour proposal.) That took more number-crunching power than mechanical desk-calculators could supply, but it's nothing compared to what's going on these days with Cassini or the earlier Galileo probe to Jupiter, both of which extensively use orbital flybys of moons to alter their orbital inclination and set up subsequent encounters. There is also a case recently of a comsat which failed to make geosynchronous orbit due to insufficient fuel -- but which was rescued over a six month period by some minor trajectory tweaks timed carefully to use earth-moon-sun conjunctions to alter its orbit until it was within reach of GEO. There's now work on using three-body interactions to move probes from high earth orbit directly onto interplanetary trajectories without needing an upper stage burn, and the implication -- cheap (albeit slow) travel anywhere in the solar system -- is noteworthy (for our robots, anyway).

461:

At 1000g of acceleration, to reach 1% of c, you'd need a distance of (use V^2=2as) 450,000 km. Which would be a very long linear accelerator. I think that building any intelligence into the bullets would be quite hard, it would have to stand an enourmous acceleration.

Conversely, to hit a 1km target at 1 light year would involve aiming the front of an accelerator 450,000km. The target is about 1000 / (3 x 10^7 * 3 x 10^8) = 10/9 * 10^ -13.
The "rifle" barrel is 4.5x10^8m long, so the end can wander up to 45/9 x 10^-5 = 0.05 mm. Not that anything that long would be rigid on those scales.

462:

"not really a valid argument about long term technological progress. Why? Because it's not based on what we know about science or technology. It's based on history and psychology."

There are lots of different views about what technology is and how it progresses. First we know that technology, over the long term, does increase in capability. Secondly we know that the bulk of our technology was created since the industrial revolution. These are historical facts.

So you raise the several questions. Is this looking in the rear view mirror fooling us about the future? What is the driver of technological change? What can we extrapolate?

Two authors have recently written books on technology. "The Nature of Technology: What It Is and How It Evolves", W. Brian Arthur, and "What Technology Wants", Kevin Kelly. Both seems to come to the conclusion that technology that technology proliferates because of an endogenous system of complexification simply because of the combinatorial possibilities. The more technology you have, the more you can have in the future. Kelly goes further and suggests that technology is almost living in its evolution. If they are correct, then we can posit that technology as a whole, will continue to increase, perhaps exponentially. Note that just like life, that doesn't mean that we won't see major directional changes from one form to another.

Certainly some technologies dead end as they reach the physical limits of the possible. Obviously we cannot use rockets to reach the speed of light, and the energy requirements to even get close are so huge that we may never achieve high fractional c velocities. That seems reasonable. Note that there is nothing to stop us traveling faster than c, it is just that we have no a clue on how this might be achieved, so it is magic. Since the 1960's, we have seen an explosion of computational power following Moore's law rates and we are making headway in bio technologies, although the focus on health care applications makes it seem as though progress is slow in actual products. Clearly progress in any technology is influenced by profits. If spaceflight seems hobbled since the techno-optimistic dreams of the 1960's, perhaps it has less to do with potential capability and more to do with business opportunities. As space entrepreneurs have understood, the main problem concerning low cost access to space is not the energy requirements, but rather the demand for, and capability of, reusable, vehicles. If we had spacecraft that could be used like airliners, ticket seats would fall dramatically. The trick is to get onto that demand escalator.

It is entirely possible that we abandon human spaceflight entirely and only use robotic spacecraft. In just may be that keeping monkeys alive in a can is just not a viable way to travel in space. OTOH, technology may offer us other solutions for minds to travel in space, and meat cans might look as quaint as ornithopters.

So I doubt we will "get stuck in a rut", it is just that some ideas won't happen, or at least as we might think of those ideas today, but other dreams will flower instead.

463:

Why cannot guidance systems be built into objects to withstand 1000 g's?

I see no reason why the accuracy has to be determined by the gun, rather than the "bullet". The gun delivers the necessary velocity, and the bullet uses tiny course corrections to home in on the target.

What am I missing?

464:

Even with 1000 gs, which seems very high to me, the launcher gun needed ti be 450,000 kilometers long. Ie to reach from the earth to the moon (and a little further.

I don't think we know much about engineering for 1000g of acceleration, and all in all, it just seems to be off in magic wand territory.

465:

1000g seems much too low - I believe guns today do 100x that much. (e.g. on the order of 1km/s in 0.5m) I wasn't thinking of using smart pellets, so the limit would be the strength of the pellets, which could be quite high, and also could be augmented by the fields in the accelerator. About 5E7m/s^2 (~5 million g, ~50x a gun, with pellets 50x the strength of lead/copper bullets) would allow going to 1/3c in 2s and keeping the accelerator to 100,000km (under 10x the length of the longest earth railway.) If necessary for shorter accelerators one could go to a neutral atomic beam - nuclei are plenty strong.

Aiming is too difficult to do all in one go, so I proposed using correctors which would ride the beam behind the ship. These would have to have some reaction mass to push the beam up to a few picoradians sideways.

heteromeles @455 - Yes, that seems like a more practical way to go.

466:

Sigh. It doesn`t matter what humans start to design, we always end up with a huge gun.

467:

From the WP "g-force" and "internal ballistics" articles: avg. acceleration over the first few cm of a gun barrel is ~160,000-190,000g. Artillery shell electronics is rated to 15,500g. According to NASA, the acceleration of a light gas gun is ~2,000,000g. The LHC pushes about 190 million g, and a plasma wakefield accelerator 9E20 g.

468:

On Greg's comments at 459 " Those days are still with us. They're called religious leaders, claiming the world for [insert name of preferred big sky fairy here] and his truth, and death to the unbelievers.... "

Oh, well, I do appreciate this, and of course history isn't lacking in Death Cults, but, there are some fairly harmless Nut Cult-lets you know, Greg.

Consider my own personal favorite Nut Cult-Let that is especially applicable to the Doing Horrible Things to the Planet Venus section of our Noble Host's thread, thus ....

" Copies of early issues of Cosmic Voice are now collectors' items, and so great is the demand for them that the Society's headquarters in Fulham Road have issued special edited `reprints'. These included the text of many of the first recorded transmissions from Mars, Sector 6 (and his occasional replacement, Mars, Sector 8), Aetherius and even those highly controversial communications reputed to come from Jesus Christ himself.

This latter development, which gave the Aetherius Society its first brush with the national press and brought charges of blasphemy to its door, came as a great surprise not only to the audience, but also to George King, the medium. For one or two meetings prior to the occasion, the Master Aetherius had made a number of passing references to `the Master Jesus' who, he implied, was alive and well and having on Venus. The same evidently applied to such other great religious leaders as Buddha, and Rama-Krishna. In a section, `Your questions answered', in the July 1955 issue of Cosmic Voice, it is indicated that there is nothing unique about the Immaculate Conception - this is the way all planetary masters are reborn on Venus. Furthermore, one of the first flying saucer sightings ever reported has come to be called the Star of Bethlehem and it was, of course, the space vehicle which brought Jesus to his earthly abode. "


So There! Jesus Christ is alive and has a postal address on the Planet Venus !

Just to think that there are people herein on this Topic who are talking of evicting Jesus Christ, and all manner of other Supernatural Persons from their comfortable home. See here ...

http://www.xenu-directory.net/mirrors/www.whyaretheydead.net/krasel/books/evans/jesus.html


" Today such stuff would pass pretty well unnoticed in the press, but in 1955 the climate of opinion still favoured the notion that England was an actively Christian country with an actively Christian press who were expected to take up the cudgels in the defence of the national ethic. In a swingeing attack on George King, the Aetherius Society and anyone vaguely connected with it, the Sunday Empire News - a newspaper which bit the dust in the TV boom of the late fifties - even took the line that the group were the dupes of Communism. This unusual accusation depended on the frequent warnings from Mars, Venus and elsewhere emanating through King which urged the suspension of nuclear tests and warned the world that it was rushing headlong into another major war - a theme which we have seen runs strongly through most of the contactees' stories.

The personal appearance of Jesus at the Caxton Hall also induced a great surge of interest on the part of the public and, following an attack on King by the specialist weekly paper Psychic News, tickets for future meetings sold out weeks in advance.

The voice of Jesus (it is possible to hear it by purchasing tapes from the Aetherius Society) is disappointing, not to say irritating. Nor is what he has to say particularly convincing, being mainly a collection of platitudes dressed up in a faintly New Testament style - `Lead them as you would a little child', `within each heart there burns a flame of love', etc. Nevertheless, according to contemporary accounts of the early meetings, it had a startling effect on the audience, some of whom were visibly moved to tears. Whatever the stir it caused in the fifties, the Master Jesus, speaking from Venus, still `overshadows' the leader of the Aetherius Society to this day and is a completely credible figure to most members, who accept his communications as untainted in any way with blasphemy. "

Shame on You! What has Jesus Christ done to deserve this?

469:

The question I have is, are there limits to the continued development of technology over time? If so, any exponential curve of technological improvement, no matter what the technologies used, eventually becomes sigmoid and flattens out. And how is it possible that in a universe based on law (which I'm assuming is the case of the universe we live in, otherwise science and technology wouldn't work), how could there not be limits? It may be we end up approaching the limits asymptotically, so that we can always improve things somewhat, but that still implies that there are things we're never going to be able to do.

470:

One further thought. Human spaceflight programs are non-profit, government funded exercises. They are not sustainable business enterprises which would be a driver to steadily improve key capabilities. Should that change, then we might see extensive manned deep space mission capability.

471:

Of course. And the relevance to the discussion is where on the sigmoid curve we are?

472:

Okay, 1000g is too low. Still, it's the electronics that have to survive. I like the idea of having devices riding herd on them, although that's quite a few points of failure.

473:

@ 456:

!?!?!? Very nice, if true. But on that one I'm afraid I'd have to see some cites before I believe it.


I just proposed doing the experiment to one of the research organizations (SSI) in the space field. Hopefully, citation to follow, though it would probably be a few months even if they go for it. I recall this was vaguely floated at the Space Manufacturing Conference after-hours discussions late last year but I don't know of anyone having kicked off an actual test. So I will.

I haven't got the tensile test rig to measure the resulting parts' basic mechanical properties but they have associated people at universities and in industry who should.

AWESOME!!! Assuming there is nothing intrinsically political here, I'm assuming you're going to get the green light on this one. Quite a feather in your cap if you pull this one off.

My apologies for shouting btw, but this is the sort of stuff I like to see. All too often I get my hopes up for what seem to be solid, sensible projects that have gotten the go-ahead, only to see them ignominiously yanked from the queue for no good reason or purpose that I can see. I was particularly disappointed with the Canadian Solar Sail Project in that regard - you'd think that with all that talk about one of the advantages of space construction is the fact that you can build big, flimsy structures, something that would look at the feasibility of managing the movement of big, flimsy structures would be the subject of intense and ongoing practical research.

At any rate, thanks for the heads up. Where can we go to see updates on your progress with this experiment?

474:
And the relevance to the discussion is where on the sigmoid curve we are?

Yes, and also just what is or is not possible to a civilization on the upper asymptote. For instance, it is at least conceivable that a highly-advanced technology could create artificial wormholes, which would allow FTL travel (and time travel). In fact, Kip Thorne and his students originally analyzed the physics of wormholes assuming that they would not be natural phenomena, but would have to be artificial. But we still don't know if the laws of physics allow for the creation of stable wormholes.

475:

@ 455:

I'd expected that the pellet stream would be stopped, meaning turned to plasma. Using the machine gun analogy (or better yet, the gyrojet analogy), I'm not sure that you could reverse the course of pellets and send them back without destroying them. It's probably just easier to shred them to plasma, and use the plasma for as many things as you can figure out (elemental resources, possibly shielding, fuel for lateral maneuvering) and dump the rest.

I think of this as very much the "Physicist's Solution" to the problem of high-performance space propulsion. That's not necessarily complementary, btw. Sure, it's very elegant in reducing the problem to one of optimizing for a few relevant variables. But - as always - you have to run the actual numbers after doing the initial BOTEC plausibility check.

The engineers who have to build the thing might have a few words to say about Physicists and their "elegance" :-) Sort of like those perennial arguments over BDB's vs something sexier like SSTO concept vehicles which are supposed to reduce the cost per kilo down to some absurdly low amount after working in the usual absurd initial assumptions one way or the other.

That's my long-winded way of saying that (imho) after hyping high-tech, high-energy solutions, probably the best way to go is just the pokey old generation ship. Yeah, ftl is way cool, and yeah, traveling at high fractions of c ( v > 0.1 c, that is) with some sort of suspended animation/longevity option for the crew seems more operatic. But at least the generation ship has this going for it: it's reliable (for certain values of reliable, of course.)

476:

There are lots of limits. My favorites are: the laws of thermodynamics, speed of light, stoichiometry, and the Peter Principle as it applies to invention (Innovators rise to their level of incompetence and stay there, creating disciples rather than challengers).

Stoichiometry in particular is underappreciated, but the ecologists are starting to have some real fun with it (look up Redfield ratios for an example). Basically, if you can't get all the elements you need in the right proportion, you can't build it. You can only build up to the limits of what you do have.

This is the ultimate limit for nanotechnology, because, absent cheap transmutation, your magic nano-goo can't turn a hunk of silicon dioxide into a rare earth magnet. It can do some truly amazing things with the silicon, but if it needs a bit of neodymium to do it, it's SOL.

477:

@ 457:

So why should we expect technology to keep changing at a rapid pace? History just points to ambition (and for most of it, not even that). We need to look at the natural world to see what's likely: if there's something that clearly seems useful and doable, then most likely we'll see change. If not? Well, we might discover something new, but who knows? We might get stuck in a rut too.

Hey, it's been - what? - three thousand, four thousand years since the invention of the fork? Even granted the slow pace of technological revolution up until the eighteenth century or so, how come forks look about the same today as they did a hundred years ago?

How come the application quantum mechanics to the problem hasn't given us some vastly superior utensil?

I want my Singularity Fork!

478:


> From the WP "g-force" and "internal ballistics" articles: avg. acceleration over the first few cm of a gun barrel is ~160,000-190,000g. Artillery shell electronics is rated to 15,500g.

FWIW, back around 1992 I attended a meeting at Livermore where a slightly crazy guy(*) presented a plan to use a pebble-bed reactor to power a light-gas gun to orbit stuff. In the course of the presentation it emerged, and I had no particular reason to doubt it, that current electronics were good to 30,000 g and they didn't see any reason that 100,000 wouldn't be doable.

(*) He was a brother of then-Congressman Duncan Hunter, so Livermore had to be nice to him.

479:
How come the application quantum mechanics to the problem hasn't given us some vastly superior utensil?

You're not counting the invention of the spork?

480:

How come the application quantum mechanics to the problem hasn't given us some vastly superior utensil?

It has. Haven't you noticed how sometimes peas stay on the fork and sometimes don't (English way of eating peas)? Uncertainly principle baked in.

481:
English way of eating peas

What, with honey?

482:

Lazy, SoV: the next paragraph is:

"Still, I keep thinking about the Black Beauty from the Green Hornet getting propelled forward by its pursuers' machine guns. That this seems to be a reasonably practical propulsion system says a lot about the difficulties of interstellar travel. Still, I guess it beats sleeping over a few pounds of antimatter for a century or two. "

I think a pellet stream is vaguely plausible, only because the shielding any interstellar craft needs to survive the voyage does about the same thing, except at the front of the ship. Therefore, I think it's safe to hypothesize that *if* you can build a shield that will allow the ship to survive getting hit by a bullet traveling at some fraction of C, then it's reasonable to use similar pellets to move the ship.

Beyond that, I think a ship using a pellet stream would still be a generation or sleeper ship. It's going to be slow, because a lot of the momentum transferred is going to be lost when the pellet flashes to plasma.

483:

Back of the fork, man, back of the fork.

484:

How can there be any limit, when from every piece of information we discover you can always ask - why is this so?

485:

Repeatedly asking "why" leads you to the question "why is the universe as it is". A comprehensive understanding of that perhaps will reveal there are no whys beyond that

486:

"That design's just not going to work. Reason: you're basically using steam as reaction mass, just like the Space Shuttle. The Isp is about three orders of magnitude too low for even a slow generation ship. Building a structure capable of ejecting water vapour -- or even ionized hydrogen and oxygen nuclei -- fast enough to do this particular job is, shall we say, rather challenging.

(I've been ignoring your earlier postings because they're so wrong they're just plain annoying, but you've finally overcome my ignoring-annoying-things threshold.)"

What, no steampunk generation :). After reading you reply, my cheeks started to burn red. After checking my posts, I came to conclusion that Mr. Stross was right. And here are my excuses for sloppy work. I am not a writer, this is not my native language, I am average intelligence and I am lazy.
What I did try to achieve with that desing was to reduce mass of a ship and get rid of pipes from the engine section. (trying to decrease maintenance load). Otherwise you need a high population society that have strict one boy and one girl birth-policy. (because there's no room for population explosion or it's very narrow one). And I did not even considered about fuel issue at all (lazy).
After reading Iron sky I did check this blog so that explains the delay in replay. And the next one in line for reading are Accelerando and Saturn's children. Keep up the good work.

487:

Simple solution: I try not to eat peas. (Don't like 'em.)

488:

Otherwise you need a high population society that have strict one boy and one girl birth-policy. (because there's no room for population explosion or it's very narrow one)

Not necessary. It turns out that most women don't want to spend their lives as baby factories, and if educated and given the opportunity they won't. Also, as the cost of raising children rises, family sizes come under downward pressure. I speculate that all you need on a generation ship is a policy of (a) equal rights, and (b) private rental or leasehold ownership of living space. (If the population goes up, the cost of housing will go up, which in turn acts to deter large family sizes.)

489:

George: that rocks, seriously looking forward to Shotglass Day on the ISS.

(see the RepRap blog passim)

490:

Hmmm...

"Why the universe as it is?"
"Because X."
"Why X?"

I don`t see it ending. 8-)

491:

Weren't you taught how to eat peas when you were a child, and forced to eat them at school lunches at primary school? It wasn't just me, Pink Floyd alludes to it in "The Wall" album.

How people use a fork is so ingrained, that you can use it to detect where an actor was raised even if their accent is "perfect" in a movie (and yes I know that this is useless information for you Charlie, as you cannot watch movies without difficulty). Eating peas on the back of a fork (without help from mashed potato) is sufficiently difficult and slow, that it is the equivalent of eating [non sticky] rice with chopsticks.

492:

Utensils have come through a great advance, mostly better metalurgy, which is in the end applied quantum mechanics.

Metal utensils used to be too expensive for normal people, and they were either made from weak metals, or from rusr-attracting metals. It's not that long ago that most people just had a knife and nothing else, and had to polish it all the time to keep it from rusting away.

That everyone can have a drawer full of sharp, dishwasher-proof utensils is a great stride forward...

493:

@ 460:

You missed one fundamental way space travel has changed since the 1960s: the use of gravitational slingshots, and then of chaotic orbital dynamics, to move spacecraft around with very little energy inputs . . .

There's now work on using three-body interactions to move probes from high earth orbit directly onto interplanetary trajectories without needing an upper stage burn, and the implication -- cheap (albeit slow) travel anywhere in the solar system -- is noteworthy (for our robots, anyway).

Which just underscores the fact that in space the natural pace of things is slooow. I can believe in life - even intelligent life - trafficking regularly between the stars. But my suspicions are that it will be more like the cometary-based uber-intelligences in Wilson's Spin or Hoyle's Black Cloud. Not for people like us.

And really, wanting energetic travel at high speeds is just a byproduct of our biological processes. I'm fond of pointing out that the only reason ftl is something of other than academic interest is because the stars are so far away; if we lived in a globular cluster like M72 where there's about a million stars within a radius of 21 light-years, well, 21 divided by the cube root of a million times two works out to an average of just 0.42 light-years between stars. On average. Now your generation ship takes just two generations to get to the nearest star, and round-trip journeys can be made in a single (moderately) extended lifetime. Heck, even using the very best reasonably plausible spacecraft propulsion - constant one gee acceleration - won't give you enough of a runway to get up much past 1/2 c.

I guess what I'm saying is that, realistically speaking, given the natural scale of the setting, maybe people should just resign themselves to the idea that travel even to the nearer stars is going to be on the order of half a millenium, minimum. We're small creatures living in a big sky.

494:

Some general comments on Space Elevators:

1) Yes, there have been some "wins" recently in beam powered climber testing - however - having spoken to several of the team members who won, they're all pretty negative about the prospects of an elevator on an Earth sized planet.

2) The issue with speed of climber isn't just the atmosphere - the current designs use wheels clamped to the cable, which limits the speed the climber can climb to a few hundred KPH - if you're lucky. They also represent a mechanical nightmare - there aren't a lot of trains that do 30,000kms in continuous, non-stop, service.

3) There's a bunch of stuff that hasn't been researched very well - not least of which, the cable/ribbon will flex and rotate - basic calcs done show this will lead to the cable having to deal with 400K+ temperate changes from side to side of a thin cable - all of which happen in seconds as the cable flexes into the sun and out again. For something essentially made of carbon this is sub-optimal.

If you bump into him at a con and he's not sick of talking about it already, I recommend spending an hour chatting to Jordan Kare about the problems of building an elevator...

495:

Fair enough, but aren't you confusing Want with Need? ..that is to say the Need ? Of, say, a very artificial society in which the female Colonists/Crew Members may well be expected to be the incubators of the SEED of, say the Religious/Political Leader Prophet of choice ?

Equal Rights is all very well but it is a pretty new concept even in western/Democratic political terms and even there there is the possibility of the Very Wealthy Christian Religious Right of the US of A liens deciding to equip their very own inter- planetary/ Generation Star Ship Colony with their own idea of the Proper Place for Women ... or Men if it comes to that, though a Matriarchy would be a bit of a stretch from the the Religious/and or Political entities that we have now and are likely to have in the next few hundred years.

496:

Oops, forgot to add ...


http://www.telegraph.co.uk/family/8276156/Surrogacy-the-brave-new-world-of-making-babies.html

And She isn't even a Dear Leader.

497:

@ 482:

Lazy, SoV: the next paragraph is:

Ah, I'm not disagreeing with you at all. Sorry if it came across that way (though my point is actually sort of orthoganol to yours.)

I think a pellet stream is vaguely plausible, only because the shielding any interstellar craft needs to survive the voyage does about the same thing, except at the front of the ship. Therefore, I think it's safe to hypothesize that *if* you can build a shield that will allow the ship to survive getting hit by a bullet traveling at some fraction of C, then it's reasonable to use similar pellets to move the ship.

Well, like I said, you don't need any solid material to intercept the pellet - and anyway the mass of a physical catcher goes as the square of the radius; not good.[1]

But that's not what I was trying to get at, so let me try again: What's the "best" way to conserve oil for transportation? Should we apply engineering know-how to manufacturing a car that increases fleet mileage, going from 40 miles per gallon to, say, 70 mpg (29.7 km/l)? How about coming up with a car that doesn't use gasoline at all, say electric or compressed air or whatever? Or maybe we should invest heavily in public transportation infrastructure? How about throwing in some social machinery and requiring everyone to car pool?

As it turns out, none of those things.

The best way to conserve oil right now is simply to junk any older car that gets less than, say, 25 mpg (10.6 km/l) and buy a newer car that gets 40 mpg (17 km/l). Leaving aside the other solutions, it may seem weird weird that going from 40 to 70 mpg gives less of an improvement than going from 25 to 40 mpg (if nothing else 70/40=1.75>1.6=40/25), but its true. For a trip of 1400 miles, the 70 mpg machine uses 20 gallons while a 40 mpg vehicle uses 35, a savings of 15 gallons (57 l). Otoh, going from 25 to 40 saves 56-35=21 gallons (80 l), a difference of six gallons (or 23 l).

So in this case, the lower-tech solution is actually the best one in terms of resources saved. Moreover, while the better engineered cars may in some sense be called an aesthetic improvement over the older ones, from an engineering standpoint, they're a much bigger headache.

And really, that's all I meant with that comment. Yes, pellet propulsion is way cool in the abstract, and yes, it can get some sort of ship up to 0.2 c without too many difficulties (relatively speaking, of course.) But using the tested and true (by that time) techniques for long-term high-population habitats, fission power, etc. might be the better way to go in the long run. Sure, it's slower. But you'll get there with what you need with some reasonable certainty. And since this is a one-way voyage anyway, I'd rank trip time as relatively low on the list of priorities.


[1]It's a side point, but . . . lets run the numbers. Assuming you had some sort of catching mechanism 10,000 km across, at one light-year out it will subtend an angle of 10e7/10e16=10e-9 radians. Call it a target of about 10e-4 arcsecs across that the pellets have to intercept. Ouch! Now, that's still within the realm of possibility - when Gaia comes on line sometime with the next three years, it will be able to measure angles on the order 10e-5 arcsecs, and that's with early 21 century technology. However, at the far end . . . a material catcher 10,000 km across seems to be a bit on the large side, particularly if it has to stop bits of metal moving at a substantial fraction of c. You might be able to hit the target, but in terms of any useful velocity changes . . . If you use a current carrying loop however, the mass problem becomes much more tractable. It's only the perimeter of the catcher that masses anything then, and perimeter scales linearly rather than as a square.

498:

What a load of b... I mean, of wasted time. People should concentrate on the most important thing - the cable. It, at least, can have other implementations.

499:

Er... not sure what your point is here?

Building cables like that is one thing, a Space Elevator is another. If you're building a Space Elevator you can't ignore the hard problems to concentrate on the bit you're interested in.

That's why I think engineers should be taught a metric sh1tload more systems, manufacturing and production engineering in their degrees than they usually are.

500:

My point is, a strong cable can be used here and now in lots of ways, while designing Space Elevator infrastructure is an exercise in futility.

501:

and if we can run a self-contained and unreprovisioned habitat there for a century, then we can probably strap a propulsion system to it and run it for a century-long interstellar cruise.

We run into a problem here: who is going to run this thing? An century-long experiment is going to last longer than most governments.

We do have one institution in the West that has experience with running projects that last for centuries, has a long-range planning horizon - the Roman Catholic Church.

502:

I had exactly those same experiences you describe, which is why I will go out of my way (to this day) to avoid certain substances which are mistakenly described as "food". (Not that I was taught cutlery usage at school -- I got it at home, first.)

503:

Ahem. I wouldn't characterise a space elevator as futile per se.

I agree that the problems with building a classic Clarkian surface-to-GEO space elevator on Earth are formidable and it's unlikely to be a viable engineering proposition any time soon.

However, a polar-to-L1 elevator on the Moon is another matter. Less energy required to run a climber, constant sunlight (if we want to consider solar powered climbers), and a much lower support strength for the cable. It's not suitable for human access to the Lunar surface (56,000Km at low speed with radiation exposure!) but for moving freight and or scientific payloads it's a goer. There are no problems with atmospheric turbulence, and we don't even need woven fullerene fibre -- Kevlar or Spectra have sufficient tensile strength.

(Whether we want a substantial outpost on the Moon is another matter -- but if we do, this is the right way to do surface resupply/resource extraction.)

Mars is another candidate, and although there's an atmosphere to consider it's much thinner. Also: shallower gravity well than Earth, and a much lower synchronous orbit -- 17,100Km (compared to 35,700Km on Earth).

Venus is probably a non-starter: near-Earth mass combined with hideous atmospheric properties and no stable synchronous orbit closer than the L1 or L2 points.

Finally, we might well be able to use a non-synchronous skyhook in Earth orbit. It wouldn't be anything like as elegant as a full-on space elevator, but it ought to be achievable with today's materials and a suitable carrier aircraft and provide a good shortcut into LEO. Moreover, there's David Brin's proposal to run a current through a closed loop of wire cutting through the Earth's magnetic field and use it as a motor for orbital adjustment; this might allow a non-synchronous skyhook to maintain its orbital inclination and altitude without blowing out fuel despite yanking numerous payloads into orbit. The problems seem to lie in the tether dynamics, and we're still in the very early days of discovering just how to unroll a long, strong cable in orbit.