Ion Propulsion

Ion thrusters have high specific impulses—ratio of thrust to the rate of propellant consumption using significantly less propellant needed for chemical propulsion, unfortunately Ion thrust engines are practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Spacecraft rely on conventional chemical rockets to initially reach orbit.

Most Ion thruster have been low powered to date but Elon Musk has mentioned look at high power Ion drives for interplanetary travel.

See also plasma Magnetic sail