NASA’s Deep Space 1 spacecraft, launched on 24 October 1998, was propelled to its target, Comet Borrelly, by a revolutionary type of engine. A beam of ionized xenon atoms were expelled from the engine at 35km/s (21 miles/s), providing a thrust of 0.09 Newtons (0.02 lbs), equivalent to the force exerted by a sheet of paper resting on the palm of a hand. The ion engine was ten times more efficient than a chemical rocket and was fired for 16,265 hours during the mission.

NASA is the National Aeronautics and Space Administration of the USA