Re: The Moon Could Meet the World's Energy Needs for 10000 y
Posted: Fri 08 Aug 2014, 10:21:20
KaiserJeep - It's not so much rejecting the proposal because it is a clean, carbon free source of electrical power. But because it doesn't make sense, at all. The economics don't make sense. The technologies needed don't exist. And there are better alternatives here on earth that are infinitely more viable than lunar HE3 mining.
Helium-3, Lunar ChimeraLunar Helium-three (3He) has been widely promoted as a killer ap for Lunar development; supposedly offering aneutronic fusion to an energy-starved world, helium three is pitched as something that is in short supply on Earth but common on the Moon, apparently the ideal raw material around which to justify the investment needed for Lunar development. In actual fact, lunar 3He is a complete chimera; it is not common on the Moon, it cannot deliver true aneutronic fusion, it is subject to replacement by terrestrial materials, and in fact our civilization is incapable of using it to generate energy at all.
Abundance
Lunar 3He reserves are pitched in such a way the seemingly large absolute quantities of 3He on the moon; phrases like “enormous reserves” are tossed around to describe the estimated millions of tonnes of 3He potentially trapped in lunar regolith. What boosters fail to highlight in press reports is that this vast reservoir is stored within a much larger amount of regolith; recovering one tonne of lunar helium-three would require processing ten million tonnes or more of regolith.
False Promise
3He is pitched as a clear thermonuclear fuel. Unlike deuterium-tritium reactions, helium-three-deuterium reactions produce no neutrons. The catch is that deuterium can fuse with itself; while half of the D-D reactions produce no neutrons, the other half do produce neutrons. This means that while a fusion reactor using helium three would be cleaner than one using deuterium and tritium, it would still produce neutrons and so cannot be said to be a clean reaction; admitting to the neutron issue would mean admitting that the same mitigating technologies required for D+T reactors would be required for 3He+D reactors, although admittedly to a lesser degree. 3He+D is also harder to fuse than D+T. This means the payoff for power used to induce fusion will be smaller and the cost per kilowatt-hour produced smaller than for D+T fusion; reduced neutron emission comes at a cost.
Terrestrial replacements
There is a potential fusion reaction that is more truly aneutronic than 3He+D, one that uses boron-eleven; 11B +p yields helium; unfortunately like the 3He+D reaction, there will be side-reactions, in particular 11B reacting with alpha particles, that will produce neutrons but these will produce somewhat fewer neutrons overall than the side-reactions for 3He+D. Like 3He based fusion, 11B fusion is more difficult to initiate than D+T fusion and so will be more expensive than D+T but 11B has one great advantage over 3He; boron is a reasonable common substance on Earth and about 80% of it is 11B. Unfortunately from the point of view of a space proponent, the ease of acquiring boron on Earth is counterproductive; if you can order the stuff from a mundane chemical supply company, there is no need to go into space to get it.
We don't have commercial fusion power plants, not even D+T fusion power plants
This is the giant cephalopod on the kitchen table that lunar 3He boosters have to ignore because without fusion plants, it hardly matters if the reaction the plants would use produce an abundance of neutrons or a dearth of them. Without fusion generators, there's no demand for 3He, lunar or not, as a fusion fuel. Without fusion plants, there's no market for lunar 3He as a fusion fuel. Sadly, a thorough audit of the power-generating facilities of the world reveals a complete lack of commercial fusion power plants. This is because we have currently lack the know-how needed to build commercial fusion power plants. Not only are we currently incapable of building the devices on which the lunar 3He scheme is utterly dependent but it does not seem very likely that we will acquire the required skills any time soon; although research is ongoing commercial fusion is at best decades away, perhaps longer. ITER, a showcase project for fusion research, is only intended to produce more energy than it consumes rather than producing energy cheaply enough for sale; commercial exploitation of the information produced by ITER will have to follow the complete of that program in 2038 and will presumably involved D+T reactions, not the far more difficult D+3He reactions. It is arguably possible that most of the people reading this will be dead before commercial fusion is developed.