Navigation of the Deep Space 1 spacecraft at Borrelly

The navigation challenges posed by Deep Space 1's flyby of comet Borrelly were considerable due to the uncertainty in the knowledge of the comet's ephemeris, as well as difficulty in determining the spacecraft's ephemeris caused by relatively large non-gravitational forces acting on the comet. The challenges were met by using a combination of radio, optical, and interferometric data types to obtain a final fly by accuracy of less than 10 km.