Can we harness energy from outer space?

Using helium-3 from the moon in nuclear fusion reactions could power the Earth without giving off any pollution. See more green science pictures.
HowStuffWorks 2008

People have been searching for clean alternative energy sources for decades to no avail. As soon as one source seems to pass the test, someone uncovers its fatal flaw. Nuclear, wind, solar and hydropower have all been dragged through the mud to some degree. Traditional nuclear fission is too risky, winds aren't consistent, the sun doesn't always penetrate the clouds and hydropower dams disrupt natural environments.

It seems like any workable solution is light-years away -- literally. Some researchers think the an­swer to our energy needs rests in the stars. From wind turbines on Mars to helium-3 fusion, people are increasingly looking to extraterrestrial sources for the Earth's energy needs.

One of the sources they're looking at is helium-3 to use in nuclear fusion reactions. As opposed to nuclear fission, which splits an atom's nucleus in half, nuclear fusion combines nuclei to produce energy. While nuclear fusion has already been tested with the hydrogen isotopes deuterium and tritium, those reactions give off the majority of their energy as radioactive neutrons, raising both safety and production concerns. Helium-3, on the other hand, is perfectly safe. It doesn't give off any pollution or radioactive waste and poses no danger to surrounding areas.

An isotope of the element helium, helium-3 has two prot­ons but only one neutron. When it's heated to very high temperatures and combined with deuterium, the reaction releases incredible amounts of energy. Just 2.2 pounds (one kilogram) of helium-3 combined with 1.5 pounds (0.67 kilograms) of deuterium produces 19 megawatt-years of energy [source: Artemis]. Roughly 25 tons of the stuff could power the United States for an entire year [source: Wakefield].

The only problem is we don't have 25 tons of helium-3 just lying around. But conveniently, the moon does. In fact, scientists estimate our lunar rock contains more than 1 million tons of the element. The energy stored in that much helium is 10 times the amount of energy you'd find in all the fossil fuels on Earth [source: Artemis]. If you put a cash value on it, helium-3 would be worth $4 billion a ton in terms of its energy equivalent in oil [source: Wakefield].

The only issues that remain are the practicalities of extracting the helium and fine-tuning the fusion process. Current fusion reactors have yet to achieve the sustained high temperatures needed to produce electricity, and helium-3 extracted from the lunar surface would require lots of refining since it exists in such low concentrations in the soil.

The most promising space-based fuel source seems to be one we already have here on Earth. Find out why even the Pentagon is looking beyond our own backyard for solar power on the next page.