NASA’s Deep Space 1 was the first mission to use an ion engine as its primary propulsion system.
Launched on October 24, 1998, Deep Space 1 was a technology-demonstration mission designed to test advanced systems for future exploration. Its most important experiment was the ion propulsion system, which accelerated xenon ions electrically to create a very small but continuous thrust.
Unlike a chemical rocket, an ion engine does not provide a powerful launch impulse. Instead, it can operate for long periods and gradually build up a spacecraft’s speed while using propellant efficiently. Deep Space 1’s engine exceeded its original demonstration goal and powered the spacecraft during an encounter with asteroid 9969 Braille and later comet Borrelly.
NASA’s Dawn mission later used ion propulsion to orbit both Vesta and Ceres. Dawn was not the first mission to use the technology, although it became one of the best-known examples of deep-space ion propulsion.