VASIMR Plasma Rocket Passes Power Test, Announces Launch Date Popular Science

Spacecraft headed to Mars or beyond may harness a new source of propulsion that could refuel almost anywhere in the solar system. Last week, the VASIMR prototype plasma rocket achieved 200 kilowatts of power, the milestone the team was striving for. Now they are beginning development of a flight-capable version, slated for launch in 2013.
Rockets since the dawn of the space age have relied on burning solid or liquid chemical propellants very quickly to reach high velocities. By contrast, the plasma rocket uses an electric power source to ionize fuels such as hydrogen or helium into superheated plasma, and then directs the plasma with magnetic fields in the proper direction to create thrust.