Deep Space 1
Deep Space 1 originally was designed to test a dozen new technologies including the use of an ion engine for spacecraft propulsion. Deep Space 1 far outstripped its primary mission goals by also successfully flying by the asteroid 9969 Braille and comet Borrelly. The flybys produced what are still considered some of the best images and data ever collected from an up-close encounter with an asteroid or comet. The success of Deep Space 1 set the stage for future ion-propelled spacecraft missions, especially those making the technically difficult journey to asteroids or comets, such as NASA's Dawn mission.