Goals: Deep Space 1 was an engineering test flight for a dozen new technologies, including highly-efficient ion engines and autonomous navigation software. After its successful primary mission, scientists sent the spacecraft to get a close look -- the closest at the time -- at a comet's nucleus and structure.
Accomplishments: Despite the failure of a system that helped the spacecraft determine its orientation, the flyby was a success. Deep Space 1 -- dubbed the little spacecraft that could -- sent back excellent images and science data from a comet. Information from the flyby was used to plan several later comet missions.