Deep Space 1 Mission and observation of Comet BorrellyAfter DS1 1 completed its successful primary mission in 1999, NASA sent it on a risky and ambitious extended mission to conduct comet science. In September 2001, DSl executed a flawless encounter with comet Borrelly, yielding the best pictures and other scientific data ever collected at a comet, providing scientists with a tremendous advance in our understanding of these intriguing and important parts of the solar system.