Ion thruster. Close-up of a 7-kilowatt ion thruster being tested as part of NASA's Evolutionary Xenon Thruster (NEXT) Project. Ion thrusters are a form of electrically powered spacecraft propulsion system that create thrust by accelerating ions. An ion thruster produces small levels of thrust relative to chemical thrusters, but does so at higher specific impulse (or higher exhaust velocities), which means that it has a fuel efficiency of 10-12 times greater than a chemical thruster. The higher the rocket's specific impulse (fuel efficiency), the farther the spacecraft can go with a given amount of fuel. Given that ion thrusters produce small levels of thrust relative to chemical thrusters, they need to operate in excess of 10,000 hours to slowly