hopdavid

Website: hopdavid.livejournal.com/

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Commented on Lunch with the Astronaut
Some thought tethers were discredited when electric current fried a tether in February 1996. http://www-istp.gsfc.nasa.gov/Education/wtether.html However, they learned from that experience. A number of tethers have been launched, some of them successful. http://en.wikipedia.org/wiki/Space_tether_missions Kirk Sorensen has a number of tether...
Commented on You probably already saw this, but ...
(Reading your post 108...) I don't see that you have a clue that the constraints and requirements of ascent from earth's surface is quite different from an orbital burn. Ascending through a thick atmosphere up the slopes of a steep...
Commented on You probably already saw this, but ...
I was saying re-entry abuse is one the factors that make reusable earth to orbit vehicles difficult (if not impossible). The 10 km/sec to LEO delta V budget likely mandates multi-stage expendables even without thermal protection. Add in re-entry abuse,...
Commented on You probably already saw this, but ...
Please see my post 112. Launching from earth's surface you want a dense, high thrust propellent to minimize drag and gravity loss. In orbit, gravity loss is not an issue. It makes more sense for an upper stage to use...
Commented on You probably already saw this, but ...
Besides being easier to handle, kerosene has a better thrust to weight ratio. In general, better ISP means worse thrust. The initial part of the trip to orbit must be a vertical ascent. Gravity loss is incurred during vertical ascent....
Commented on You probably already saw this, but ...
Any power source generates heat. Whether nuclear, fossil fuels, what have you. The human generated power is a minute amount compared to what the sun gives the earth. Power generation may contribute noticeably to warming if it generates green house...
Commented on You probably already saw this, but ...
Please see my post 47 above. A mirror with perfect optics at Molniya apogee would project an image of the sun about 370 km in diameter. About the size of state of Massachusetts. You would need a photovoltaic array of...
Commented on You probably already saw this, but ...
Yes, it would likely be difficult mining lunar propellant. How difficult? Some factors to consider: The elevated CPR found by Chandrayaan-1's mini Sar radar seems to indicate sheets of ice at least two meters thick. Lunar light lag is only...
Commented on You probably already saw this, but ...
Given perfect optics, the diameter of the image projected by the mirror will be ((distance from mirror to image)/(distance to sun)) * diameter sun. A Molniya's orbit apogee has an altitude of about 40,000 km. The projected image of the...
Commented on You probably already saw this, but ...
Propellant depots could drastically decrease the complexity. As delta V budget climbs, you rapidly reach an undoable mass fraction. At this point you start discarding mass in the form of expendable stages. More stages mean more mass, complexity and failure...
Commented on You probably already saw this, but ...
Both moon and Mars are inhospitable vacuum. The chief selling point for Mars has been CHON. But LRO and Chandrayaan-1 have found CHON at the lunar poles. Not only is water useful for life support and radiation shielding but it...

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Charlie Stross commented on Lunch with the Astronaut
If NASA is bloated and useless, what does that make other countries' space programs? The Soviets, on about a quarter the budget, nearly got to the Moon with a cosmonaut. If Apollo 11 hadn't pipped them to the post they'd probably have made it in 1971 or 1972 -- they'd nearly ironed the bugs out of the N1 engine management system when the program was cancelled due to Neil Armstrong planting that flag and Brezhnev not wanting the embarrassment of coming in second (or worse, a speculacular and lethal public failure). As it is, they ran a very solid space...
brucecohenpdx commented on Lunch with the Astronaut
ISTM that a lot of the bloat came from very bad choices in mission requirements. That's basically what sunk the shuttle: it had to do everything from acting as a first stage for launching geosynch and interplanetary satellites, to on-orbit repairs, to polar military surveillance missions (and then the USAF pulled out of the program, leaving the shuttle holding the bag for missions it would never fly). That's not very different from what happened to the JSF: it turns out that the supersonic jet missions it was designed for isn't terribly relevant to current military requirements (we have interceptors and...
Charlie Stross commented on Lunch with the Astronaut
The ability to retrieve satellites on orbit was seen as a driving factor in the design. Also, I believe it was design so that it wouldn't have to de-orbit over the USSR, which added more constraints to the design process. Capabilities which were, in fact, never used in combination, but which fundamentally compromised the design. So: the shuttle was used, but not as intended -- and arguably was unfit for [eventual] purpose. The real tragedy was that it was effectively a prototype; if they'd build two and flown 30-40 missions during the early 1980s, while working on a Version 2...
bjacques commented on Lunch with the Astronaut
Late to the party--it looks like most points of the post have been answered. (Disclosure: I worked at NASA-JSC 1986-1996 doing a number of things, ending as a flight controller the final 3 years) In Commander X;'s defense, I was there when the TSS missions failed spectacularly. The technology has been proven since, but first impressions are the most lasting. The Shuttle trailing a big snarl of yarn across the night sky was a pretty embarrassing image. I think the astronaut might have been there too, at least as a candidate, and was reliving a trauma. I can't speak to...
Moderator Alan commented on Lunch with the Astronaut
Yes. That link was mentioned nearly a week ago, and expanded upon in hopdavid's comment at #47. Do you have anything to add?...

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Common Misconceptions About Publishing—a series of essays about the industry I work in.
How I Got Here In The End —my non-writing autobiography, or what I did before becoming a full-time writer.
Unwirer—an experiment in weblog mediated collaborative fiction.
Shaping the Future—a talk I gave on the social implications of Moore's Law.
Japan: first impressions — or, what I did on my holidays
Inside the MIT Media Lab—what it’s like to spend a day wandering around the Media Lab.
The High Frontier, Redux — space colonization: feasible or futile?
“Nothing like this will be built again”—inside a nuclear reactor complex.
Old blog—2003-2006 (RIP)

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