In space, however, these rockets are inefficient—they burn through huge quantities of fuel while generating more thrust than necessary. That’s why researchers are increasingly turning to nonchemical propulsion systems, which could drastically lighten spacecraft while achieving higher speeds.
Some of the ideas being researched, like antimatter engines, depend on established physics but go far beyond current technology.
“Someone’s got to think beyond the obvious,” says Marc Millis, a propulsion physicist at NASA’s Glenn Research Center. “You have enough other people in the world doing the next obvious thing. By reaching beyond that, you can discover the breakthroughs other folks aren’t even looking for, and change everything.”
A. Solar Sail
Max speed: 200,000 mph
How it works: Photons strike an immense sail of ultrathin material. Earth- or space- based lasers or particle beams could add initial oomph. Solar-sail ships go faster the longer they travel.
Tradeoffs: The dynamics of spaceflight could damage the fragile spacecraft—and micrometeorites could kill them.
Update: The Planetary Society plans to launch a 105-square-foot solar-sail craft into space this fall.
Max speed: 220,000 mph
How it works: Electrically charged molecules shoot from the engine to propel the ship. A nuclear reactor or solar cells provide the electricity.
Tradeoffs: Ion engines can’t overpower Earth’s gravity, but in space they require little fuel.
Update: NASA used an ion engine in its Deep Space 1 mission in 1998. MIT engineers won a 2009 PM Breakthrough Award for a less expensive design with about 10 times the thrust. And an ion engine built by Ad Astra Rocket Company may be tested at the Inter national Space Station in 2013.
Max speed: 270,000 mph
How it works: An engine harnesses the enormous energy released when matter and antimatter come into contact.
Tradeoffs: Creating enough antimatter in particle accelerators is currently impossible. The engine would also have a damaging kick and produce a lot of radiation.
Update: Penn State researchers have conceived of an engine to drive a spacecraft with shock absorbers tough enough to survive the collisions of protons and antiprotons.