Space Power

more Go out at night and look at the sky. Every star you see is a fusion reactor. Scientists would like to harness such power to propel spaceships and energize distant colonies.

Fusion, which releases energy by combining rather than splitting atoms, could in principle supply gigawatts of clean power. However, fusion propulsion systems as we understand them today would be very big, requiring a vehicle the size of the space station or Battlestar Galactica, weighing hundreds of tons - although the size might come down with research.

Fusion engines would be very efficient fuel burners with a specific impulse of 100,000 seconds. "Though we couldn't do it in 10 years, if we could launch a fusion propulsion system 10 years from now, we could send a vehicle out to catch Voyager and bring it back," says Cole. That kind of power and speed shortens the time that astronauts would be exposed to harmful cosmic radiation and the bone loss that comes from prolonged weightlessness.

Perhaps there's something even better than fusion: A thruster powered by matter-antimatter annihilation would have a specific impulse of 2,000,000 seconds, according to Cole.

more This "Penning trap" developed at Penn State University stores antiprotons.

It sounds like science fiction, but researchers are learning to create and store small amounts of antimatter in real-life labs. A portable electromagnetic antimatter trap at Penn State University, for example, can hold 10 billion antiprotons. If we could learn how to use such antimatter safely, we could impinge some on a thin stream of hydrogen gas to create thrust. Alternatively, a little antimatter could be injected into a fusion reactor to lower the temperatures needed to trigger a fusion reaction.

"Propulsion isn't the only reason to go nuclear," notes Colleen Hartman, director of solar-system exploration at NASA. "Onboard systems benefit, too. The excess power is like getting the Las Vegas strip instead of a single light bulb. It gives you greater communication and mission flexibility."

The Mars Smart Lander and Mobile Laboratory, slated for launch as early as 2009, was originally conceived as a solar-powered mission. But now researchers are considering an upgrade from solar to nuclear power: "Putting nuclear power on board will extend the mission from 3-6 months [with solar power] to 5 years [with radioisotope power]," says Ed Weiler, head of the Space Science Enterprise at NASA headquarters. "It will enable the rover to drive to a location rather than having to land there. The bandwidth for data communication goes way up, and the rover can work 24 hours a day. Everything increases by a factor of 10 when you add an RTG to a mission."