Deep Space 1 was NASA’s first spacecraft to use ion propulsion as its primary propulsion system.
Launched on 24 October 1998, Deep Space 1 was a technology-demonstration mission designed to test advanced systems for future deep-space exploration. Its ion engine used electricity to accelerate xenon ions, producing very low thrust but operating continuously for long periods.
The spacecraft successfully flew past asteroid 9969 Braille and later conducted a close encounter with comet Borrelly in 2001. Its autonomous navigation system and other experimental technologies also performed important demonstrations.
Dawn later used ion propulsion to orbit Vesta and Ceres. SMART-1, operated by the European Space Agency, also used ion propulsion, but it launched after Deep Space 1.