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.


One Small Step for Man, One Giant Leap for Solar Power

A solar satellite like this would receive eight times more sun than one on Earth.

Despite the fact that solar power is at our fingertips, there are benefits to outsourcing it beyond the stratosphere. Aside from the more obvious reason of avoiding the large land-use footprint presented by collections of solar panels, there's the fact that the sun actually does shine brighter on the other side of the fence. In this case, eight times brighter [source: Hanley].

Without the obstacles like rain, clouds and nighttime, solar arrays based in space would receive more concentrated solar rays than they would on Earth. The panels also wouldn't be subject to the seasonal fluctuations that are unavoidable on Earth.


Space solar power, or SSP, would basically work the same way that regular solar power works. The only difference is that the solar panels would either be attached to orbiting satellites or stationed on the moon (in which case it would be called lunar solar power, or LSP). The electricity created would be converted into microwaves and beamed down to Earth. Rectifying antennas, or rectennas, on the ground would collect the microwaves and convert them back into electricity.

If the concept seems like a stretch, consider that communications satellites already do something very similar when they transmit your cell phone conversations. Some people have even suggested that the solar panels could piggyback on communications satellites. In fact, one of the reasons space-based solar power has gotten so much attention is that all of the necessary equipment and technology is already developed and understood. The transmission of microwaves is old hat, and solar cells, or photovoltaics, are almost three times more efficient than they used to be [source: Philips].

Some initial proposals in the 1970s envisioned gigantic 3-by-6-mile (5-by-10-kilometer) solar panel arrays transmitting microwaves to rectifying antennas of a similar size. These geostationary satellites, 22,300 miles (36,000 kilometers) high would stay in the same place in relation to the Earth at all times. While just one of these satellites would produce enormous amounts of energy -- twice the energy output of the Hoover Dam -- launching such a big project proved to be economically impossible [source: Hanley].

Recent proposals to have smaller satellites circle the Earth continuously would be more manageable and still produce considerable energy output. A satellite less than 1,000 feet (300 meters) across orbiting 300 miles (540 kilometers) above Earth could potentially power 1,000 homes [source: Hanley]

Even the Pentagon is on board, having released a study detailing applications in powering military operations. Japan, Russia, Europe and the island nation of Palau are also looking into it. Some experts estimate a test project could be done by 2012 and that significant amounts of power could come from space before the beginning of the next century [source: Hanley].

The major obstacle right now, as with any new technology, is cost. Launching, setting up and maintaining a solar farm on the moon would require vast amounts of manpower and money. As it is now, launching an object into space costs 1,000 times more than transporting that object across the country on a plane -- even though they use the same amount of energy [source: Hoffert].

If NASA succeeds in finding a new generation of reusable launch vehicles, though, costs could go down. Not to mention the fact that a solar satellite could pay back the energy used to send it into orbit in less than five days [source: Hoffert].

Many people agree that as we start to exhaust the Earth's natural resources, looking to the heavens for an answer may not be such a bad investment. If you're one of those people, try out some of the links on the next page.


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More Great Links

  • A­rtemis. "Lunar Helium-3 as an Energy Source, in a nutshell." 2007. (July 23, 2008)
  • Hanley, Charles J. " 'Drilling Up'-- Some Look to Space for Energy." Associated Press. Dec. 26, 2007. (July 22, 2008).
  • Hoffert, Martin I. and Seth D. Potter. "Beam It Down: How The New Satellites Can Power The World." Space Future. Oct. 1997. (July 22, 2008) an_power_the_world.shtml
  • Macey, Richard. "Pentagon offers a ray of hope in energy debate." The Sydney Morning Herald. Oct. 17, 2007. (July 22, 2008). energy-debate/2007/10/16/1192300768027.html
  • Philips, Graham. "Solar Space Power." Catalyst. March 13, 2008. (July 22, 2008)
  • Singer, Jeremy. "Pentagon may study space-based solar power." April 11, 2007. (July 22, 2008).
  • Trivedi, Bijal P. "Can Earth Be Powered by Energy Beamed From Moon." National Geographic Today. April 26, 2002.
  • Wakefield, Julia. "Researchers and space enthusia