Helium-3, a lightweight isotope of the familiar helium gas, is found on Earth but in such limited quantities it could not be used as fuel for nuclear fusion. But it is available on the moon and is often cited as one of the most promising resource discoveries in space so far.
Transporting a high-value, low-volume mineral back to Earth for use here represents the next stage of mining in space, after the first stage, known as in situ resource utilization.
Apollo 17 astronaut Harrison Schmitt, a geologist, has been a leading supporter of mining helium-3 on the moon to generate nuclear fusion power on Earth.
The following is condensed from Mr. Schmitt's Mining the Moon essay that appeared in the October, 2011, issue of Popular Mechanics magazine:
Nuclear fusion powers the sun and it is of interest to scientists because of its potential to create electrical power on Earth without the dangers of radioactive byproducts produced by nuclear fission, the process now used to generate nuclear power.
Although the fusion process is understood, there is not an adequate source of helium-3, whose unique atomic structure makes it ideal as a nuclear fuel source, to use it as a fuel for nuclear fusion and to develop a fusion reactor.
But helium-3 does exist in plentiful quantities on the moon and the volumes needed to produce significant amounts of power are small enough to justify transporting back to Earth.
Just 220 pounds of helium-3 would supply enough power to run a city the size of Detroit for a year.
At a cost estimated at about $141-million, 220 pounds of helium-3 is the kind of high-value, low-volume mineral that makes mining in space for resources to be used on Earth economically viable.
The cost of the investment in mining helium-3 on the moon would be significant, comparable to the cost of building a major transcontinental pipeline.
The challenges of extracting helium-3 from the moon and returning it to Earth would be difficult. "But the potential rewards would be staggering for those who embarked upon this venture," Mr. Schmitt said. "Helium-3 could help free the United States – and the world – from dependence on fossil fuels."