Ion propulsion
Ion propulsion is a long duration, low thrust system which only requires a source of electrical energy (solar power or nuclear power) and a relatively small amount of ionizable reaction mass (such as a few hundred kilograms of Xenon gas). Small ion thrusters have been used for decades on Russian satellites for stationkeeping. Ion propulsion has also been used on more recent space exploration missions, such as the Smart-1 lunar probe and the Dawn mission to asteroids Ceres and Vesta.
