The Apollo astronauts who walked on the Moon between 1969 and 1972 brought back just under 842 pounds of rocks and regolith. In 1985, engineers at the University of Wisconsin found that some samples contained significant amount of Helium-3. Helium-3 (or He3) is a stable isotope of helium that we can use to produce clean energy through nuclear fusion. For some, it’s a way to solve the world’s energy crisis. But others see it as a little more complicated. If it can be done, it’s a long way off.
For some, mining He3 from the Moon is a compelling reason to return. It’s a rare isotope on Earth: it’s carried by the solar wind but can’t penetrate our atmosphere. It’s plentiful on the Moon because the Moon has no atmosphere to deflect the solar wind away. He3 builds up in the regolith. But before looking at the arguments for and against using lunar-derived He3 as an energy source on Earth, it’s worth taking a second to look at what sets the isotope apart and how it could be used.
Current nuclear power plants use fission reactors. Uranium nuclei are split, releasing energy that is used to turn water into steam, which in turn drives a turbine to produce electricity. What’s really attractive about fission is that the reaction is self-sustaining. Once it gets started it’s tough to stop. But the byproduct of this reaction is radioactive material. Another downside is that current reactors consume more energy than they put out.
Nuclear fusion is a different type of reaction. The same reaction that fuels the sun – high temperatures and dense concentrations of gas allow positively-charged nuclei to get close enough that the attractive nuclear force overcomes the repulsive electrical force. They fuse. This produces new elements and energy, and when helium is the fuel in this type of reaction it can provide energy without the long lived radioactive or nuclear material that fission produces. It produces a tremendous amount of energy, but it’s a hard reaction to start and sustain.
Fusion reactions that use tritium and deuterium, both isotopes of hydrogen, produce loads of energy but it’s less energy than goes in. The product of this reaction is problematic, namely because it creates neutrons. It’s hard to extract energy from neutrons, and basically everything they come into contact with turn radioactive.
Fusion reactions between Helium-3 and deuterium, on the other hand, creates somewhat less energy. The product in this reaction is helium and a proton without a neutron – it’s the lack of neutron is pretty appealing. But protons end up being a different kind of waste. They can’t be left in the reactor because they affect the continued reaction. They have to be drawn out. This costs energy, but it’s not a total waste. Those neutrons could hit a blanket of lithium to form tritium, which could decay into more He3, but not in time to go right back through the reactor.
Advocates of He3 fusion energy point out that this reaction produces more energy than a reaction with tritium and deuterium. With enough research and dedicated funding, some think we could crack the He3 fusion nut and have a clean energy source right here on Earth. And if the Moon has more of the isotope than the Earth, why not go and mine it? One outspoken advocate of mining the Moon for He3 is Jack Schmitt, Apollo 17’s lunar module pilot and the only geologist to walk on the Moon. He goes so far as to say that not returning to the Moon to mine this vital resource is immoral. We have a way to solve the global energy crisis, we have a responsibility to use that knowledge.
But there are those who see the potential benefits of He3 as fantasy. Or at least harder than the other available options.
For one it’s expensive. Though we know how to get to the Moon having been there with Apollo, we don’t currently have the technology to make returning a reality. We’d have to research, test, and build that technology – not to mention doing the same for the technology to mine the Moon and develop a system to bring He3 back to Earth. Even if there were some tourism to be gained from the venture – Ride to the Moon and back with He3! – finding an outfit to foot the bill could be incredibly difficult. Which brings up the argument that we don’t know exactly how much He3 there really is on the Moon. Is there enough up there to justify the expense of bringing it back or not?
There’s also the slight stopping block that He3 reactors haven’t been invented. If we did bring back He3 from the Moon, we’d have to figure out just how to harness the energy potential in the material. Commercial deuterium-tritium fusion plants don’t even exist yet, so commercial reactors using He3 are far in the future. It’s another substantial cost that would require another big risky investment from a confident company.
Nevertheless an attractive prospect – a single isotope providing a compelling reason to fund space research while also returning the material that will solve our energy crisis – but whether or not its practical given the difficulties involved is still a very big question mark.