On the space colonization topic — I'm flogging the dead equine until the ivory shows — it occurs to me to note that currently, whenever someone asks "who's going to pay for it?" the answer is some variation on "the Lunar He 3 will make us rich!"
For those who were asleep when the Clue Fairy rang the doorbell, the narrative goes like this:
Helium-3 is a light isotope of Helium. It is of interest because, to crib from wikipedia:
Some fusion processes produce highly energetic neutrons which render reactor components radioactive with activation products through the continuous bombardment of the reactor's components with emitted neutrons. Because of this bombardment and irradiation, power generation must occur indirectly through thermal means, as in a fission reactor. However, the appeal of helium-3 fusion stems from the aneutronic nature of its reaction products. Helium-3 itself is non-radioactive. The lone high-energy by-product, the proton, can be contained using electric and magnetic fields. The momentum energy of this proton (created in the fusion process) will interact with the containing electromagnetic field, resulting in direct net electricity generation.
He 3 looks at first sight as if it could be the key to clean nuclear power — that is, to fusion reactors that live up to the original promise of not producing shedloads of high level waste. However, He 3 is vanishingly rare on Earth.
At this point, enter, stage left, a Space Cadet: He 3 is rare, therefore it's expensive. But there's He 3 in the lunar regolith, trapped there after being blasted out by the solar wind. We should go to the moon and mine He 3! It'll solve all our energy problems!
Unfortunately there are a couple of problems.
Firstly, nobody's built a commercially successful fusion reactor yet. ITER plan to build a working test-bed; it's logical successor would be a working prototype first generation power reactor. There are huge obstacles to overcome, not least in developing neutron capture techniques and breeding D/T fuel. These are engineering problems (sorry, annoying paywall) and theoretically amenable to solution — but at a price of billions of euros and decades of work, and even then, it may turn out to be too costly to be a viable competitor for well-understood fourth generation fission technology and a mature waste disposal/fuel recycling chain. And that's before we look to a speculative second generation reactor, running on a different type of fuel, that — because of the higher Coulomb barrier between He nuclei — requires a far higher temperature (on the order of 500M to 1Bn degrees celsius, rather than the relatively chilly 100M degrees C required for D/T fusion).
Given the average generation time for a new reactor technology of 20-30 years, and development costs on the order of $50Bn-100Bn per generation, we won't be even thinking about prototyping an He3 reactor until 2060 at the earliest.
Secondly, there's very little He 3 in the lunar regolith. The amount is non-zero, but we can also breed the stuff on Earth: Neutron bombardment of Lithium, Boron, or Nitrogen targets, or decay of Tritium are currently used. Breeding He 3 requires a high neutron flux, but unless the plan is to automagically shift us all over to a "clean" He 3 power cycle instantly, He 3 reactors will be coexisting with "dirty" high-flux fission or fusion reactors for many decades.
Is it really going to be cheaper to send monster trucks to the moon, than to build a couple of special-purpose high neutron flux reactors optimized for mass production of Tritium (and thereby for production of He3 as a decay product)?
The whole Lunar He 3 mining proposition is a boondoggle, based on wishful thinking: that (a) we can make a working commercial fusion reactor (not yet proven, and will cost some tens of billions of dollars to get to that point), (b) if we run a more advanced — and much hotter — reactor on He 3 it produces somewhat fewer secondary neutrons, (c) He 3 is vanishingly rare on Earth but there is a tiny amount of He 3 in the Lunar regolith, so (d) MOON!!!11!!ELEVENTY!! WITH MONSTER TRUCKS AND BULLDOZERS!!!
He 3 is not magic high-energy pixie dust. And in the context of the space colonization debate it should be seen for what it is — a placeholder for the alchemist's stone that will turn the money-hole of a lunar colony into a profit centre: an extractable natural resource that can't be found on earth and is valuable enough to mine elsewhere. Unfortunately, the harder you look at the value proposition, the more it comes to resemble a pig in a poke.