Thursday, August 23, 2007

Moon Oil or Moonshine?

There's an article called Mining the Moon in today's email update from MIT's Technology Review. It discusses lab experiments on helium-3 fusion, several containment options, the potential for mining helium-3 on the Moon, and the fact that multiple countries (China, India, Japan, others) seem to be interested in this possibility, notwithstanding the fact that no "break even" demonstration of He3-He3 fusion (or any other kind for that matter) has yet been done. Some nuclear physicists maintain that while helium-3 fusion offers many potential advantages (especially the possibility that most of the reaction products can be charged particles rather than neutrons, allowing for control of the particles with electromagnetic fields, requiring much less shielding and producing much less nuclear waste), it's not the easiest fusion reaction to start and maintain. For background, helium-3 is an isotope of helium that has two protons and one neutron (common helium is helium-4 with two protons, two neutrons). Helium-3 is very rare on Earth but seems to be relatively common on the Moon, having been "planted" in the lunar regolith (soil) by billions of years of unprotected bombardment by high energy particles from the Sun (the Earth is protected from most of these particles by our magnetic field).

I'm still glad I chose in 1977 to get a graduate degree in optics rather than nuclear engineering, but this helium-3 fusion stuff is certainly intriguing. If we can get it to work, and develop Moon bases that can cost-effectively mine huge volumes of regolith, extract the helium-3, and ship it back to Earth (relatively small masses would provide a lot of electical power here on Earth), it could be a clean and abundant energy source for many years to come. Of course that's a lot of "ifs," and there's a lot of R&D to be done. Could the Moon be the Persian Gulf of the next century (in the "abundant source of energy" sense, not in the eternal conflict sense, I hope)? Or is it all a lot of moonshine, as at least one critic has said? It's certainly seems promising enough to invest a few billions of government and private sector R&D money every year in both the fusion and space development technologies, though I would also want to see more work on solar power satellites as another option (both might contribute to future energy supplies, and the powersats might even be built from lunar materials). Ground based solar too!

For a more detailed analysis (nearly a business plan) of the prospects for lunar helium-3 as a future energy source, Harrison Schmitt's Return to the Moon is a good place to start. It's not exactly an easy read (I read most of it last month), but it really works through the background and the problems and gets started on possible solutions. It also has tons of references.

Another good resource is this 2006 paper (The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion, 1 MB PDF) by Robert Bussard. This paper is actually not about He3-He3 fusion, but about an alternate neutron-free reaction based on fusion of protons (H+, hydrogen nuclei) and boron-11 to produce three alpha particles (helium-4 nuclei) which are charged particles that can be confined "electrodynamically." The paper summarizes years of research on small-scale prototypes for this approach, and it also sounds promising if it is truly as scalable as the author suggests. One of Bussard's interests in this is approach is as a high-efficiency space propulsion system (more info here). Bussard is also known for the Bussard ramjet space propulsion concept, which also uses fusion, but "scoops up" its hydrogen fuel from the interstellar medium, potentially solving the fuel mass problem for interstellar journeys.

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