Mining the Moon

Lab experiments suggest that future fusion reactors could use helium-3 gathered from the moon.
By Mark Williams

Hot gases: Researchers at the University of Wisconsin-Madison’s Fusion Technology Institute are testing this fusion reactor, shown with a view of the grid in which interial electrostatic confinement takes place. Credit: Fusion Technology Institute-University of Wisconsin-Madison


At the 21st century's start, few would have predicted that by 2007, a second race for the moon would be under way. Yet the signs are that this is now the case. Furthermore, in today's moon race, unlike the one that took place between the United States and the U.S.S.R. in the 1960s, a full roster of 21st-century global powers, including China and India, are competing.
Even more surprising is that one reason for much of the interest appears to be plans to mine helium-3--purportedly an ideal fuel for fusion reactors but almost unavailable on Earth--from the moon's surface. NASA's Vision for Space Exploration has U.S. astronauts scheduled to be back on the moon in 2020 and permanently staffing a base there by 2024. While the U.S. space agency has neither announced nor denied any desire to mine helium-3, it has nevertheless placed advocates of mining He3 in influential positions. For its part, Russia claims that the aim of any lunar program of its own--for what it's worth, the rocket corporation Energia recently started blustering, Soviet-style, that it will build a permanent moon base by 2015-2020--will be extracting He3.
The Chinese, too, apparently believe that helium-3 from the moon can enable fusion plants on Earth. This fall, the People's Republic expects to orbit a satellite around the moon and then land an unmanned vehicle there in 2011.
Nor does India intend to be left out. (See "India's Space Ambitions Soar.") This past spring, its president, A.P.J. Kalam, and its prime minister, Manmohan Singh, made major speeches asserting that, besides constructing giant solar collectors in orbit and on the moon, the world's largest democracy likewise intends to mine He3 from the lunar surface. India's probe, Chandrayaan-1, will take off next year, and ISRO, the Indian Space Research Organization, is talking about sending Chandrayaan-2, a surface rover, in 2010 or 2011. Simultaneously, Japan and Germany are also making noises about launching their own moon missions at around that time, and talking up the possibility of mining He3 and bringing it back to fuel fusion-based nuclear reactors on Earth.
Could He3 from the moon truly be a feasible solution to our power needs on Earth? Practical nuclear fusion is nowadays projected to be five decades off--the same prediction that was made at the 1958 Atoms for Peace conference in Brussels. If fusion power's arrival date has remained constantly 50 years away since 1958, why would helium-3 suddenly make fusion power more feasible?
Advocates of He3-based fusion point to the fact that current efforts to develop fusion-based power generation, like the ITER megaproject, use the deuterium-tritium fuel cycle, which is problematical. (See "International Fusion Research.") Deuterium and tritium are both hydrogen isotopes, and when they're fused in a superheated plasma, two nuclei come together to create a helium nucleus--consisting of two protons and two neutrons--and a high-energy neutron. A deuterium-tritium fusion reaction releases 80 percent of its energy in a stream of high-energy neutrons, which are highly destructive for anything they hit, including a reactor's containment vessel. Since tritium is highly radioactive, that makes containment a big problem as structures weaken and need to be replaced. Thus, whatever materials are used in a deuterium-tritium fusion power plant will have to endure serious punishment. And if that's achievable, when that fusion reactor is eventually decommissioned, there will still be a lot of radioactive waste.
Helium-3 advocates claim that it, conversely, would be nonradioactive, obviating all those problems. But a serious critic has charged that in reality, He3-based fusion isn't even a feasible option. In the August issue of Physics World, theoretical physicist Frank Close, at Oxford in the UK, has published an article called "Fears Over Factoids" in which, among other things, he summarizes some claims of the "helium aficionados," then dismisses those claims as essentially fantasy.
Close points out that in a tokamak--a machine that generates a doughnut-shaped magnetic field to confine the superheated plasmas necessary for fusion--deuterium reacts up to 100 times more slowly with helium-3 than it does with tritium. In a plasma contained in a tokamak, Close stresses, all the nuclei in the fuel get mixed together, so what's most probable is that two deuterium nuclei will rapidly fuse and produce a tritium nucleus and proton. That tritium, in turn, will likely fuse with deuterium and finally yield one helium-4 atom and a neutron. In short, Close says, if helium-3 is mined from the moon and brought to Earth, in a standard tokamak the final result will still be deuterium-tritium fusion.
Second, Close rejects the claim that two helium-3 nuclei could realistically be made to fuse with each other to produce deuterium, an alpha particle and energy. That reaction occurs even more slowly than deuterium-tritium fusion, and the fuel would have to be heated to impractically high temperatures--six times the heat of the sun's interior, by some calculations--that would be beyond the reach of any tokamak. Hence, Close concludes, "the lunar-helium-3 story is, to my mind, moonshine."
So, is He3-based fusion untenable? In fact, Close is correct in his claims about how impracticable both deuterium-helium-3 fusion and pure helium-3 fusion in tokamak-based reactors would be. But there might be alternatives. For example, Gerald Kulcinski, a professor of nuclear engineering at the University of Wisconsin-Madison, has maintained the only helium-3 fusion reactor in the world on an annual budget that's barely into six figures.
Kulcinski's He3-based fusion reactor, located in the Fusion Technology Institute at the University of Wisconsin, is very small. When running, it contains a spherical plasma roughly 10 centimeters in diameter that can produce sustained fusion with 200 million reactions per second. To produce a milliwatt of power, unfortunately, the reactor consumes a kilowatt. Close's response is, therefore, valid enough: "When practical fusion occurs with a demonstrated net power output, I--and the world's fusion community--can take note."
Still, that critique applies equally to ITER and the tokamak-based reactor effort, which also haven't yet achieved breakeven (the point at which a fusion reactor produces as much energy as it consumes). What's significant about the reactor in Wisconsin is that, as Kulcinski says, "We are doing both deuterium-He3 and He3-He3 reactions. We run deuterium-He3 fusion reactions daily, so we are very familiar with that reaction. We are also doing He3-He3 because if we can control that, it will have immense potential."
The reactor at the Fusion Technology Institute uses a technology called inertial electrostatic confinement (IEC). Kulcinski explains: "If we used a tokamak to do deuterium-helium-3, it would need to be bigger than the ITER device, which already is stretching the bounds of credibility. Our IEC devices, on the other hand, are tabletop-sized, and during our deuterium-He3 runs, we do get some neutrons produced by side reaction with deuterium." Nevertheless, Kulcinski continues, when side reactions occur that involve two deuterium nuclei fusing to produce a tritium nucleus and proton, the tritium produced is at such a higher energy level than the confinement system that it immediately escapes. "Consequently, the radioactivity in our deuterium-He3 system is only 2 percent of the radioactivity in a deuterium-tritium system."
More significant is the He3-He3 fusion reaction that Kulcinski and his assistants produce with their IEC-based reactor. In Kulcinski's reactor, two helium-3 nuclei, each with two protons and one neutron, instead fuse to produce one helium-4 nucleus, consisting of two protons and two neutrons, and two highly energetic protons.
"He3-He3 is not an easy reaction to promote," Kulcinski says. "But He3-He3 fusion has the greatest potential." That's because helium-3, unlike tritium, is nonradioactive, which, first, means that Kulcinski's reactor doesn't need the massive containment vessel that deuterium-tritium fusion requires. Second, the protons it produces--unlike the neutrons produced by deuterium-tritium reactions--possess charges and can be contained using electric and magnetic fields, which in turn results in direct electricity generation. Kulcinski says that one of his graduate assistants at the Fusion Technology Institute is working on a solid-state device to capture the protons and convert their energy directly into electricity.
Still, Kulcinski's reactor proves only the theoretical feasibility and advantages of He3-He3 fusion, with commercial viability lying decades in the future. "Currently," he says, "the Department of Energy will tell us, 'We'll make fusion work. But you're never going to go back to the moon, and that's the only way you'll get massive amounts of helium-3. So forget it.' Meanwhile, the NASA folks tell us, 'We can get the helium-3. But you'll never get fusion to work.' So DOE doesn't think NASA can do its job, NASA doesn't think that DOE can do its job, and we're in between trying to get the two to work together." Right now, Kulcinski's funding comes from two wealthy individuals who are, he says, only interested in the research and without expectation of financial profit.
Overall, then, helium-3 is not the low-hanging fruit among potential fuels to create practical fusion power, and it's one that we will have to reach the moon to pluck. That said, if pure He3-based fusion power is realizable, it would have immense advantages.
Source: http://www.technologyreview.com