Abstract: Electric propulsion (EP) is an important technology for NASA. It has played a major role on three missions, namely Deep Space 1, Dawn and Space Technology 7, and it is planned for use on many more. The ion propulsion system for the ongoing Dawn mission has achieved several notable accomplishments, including providing a total velocity change (delta-V) of over 11 km/s to the spacecraft. As a result of these successes, solar electric propulsion (SEP) is now broadly recognized as an essential tec…