ASTROMETRY FOR THE GALILEO MISSION .1. ASTEROID ENCOUNTERS

Optical CCD astrometry was done at the U.S. Naval Observatory FIagstaf f Station to obtain positions of solar system bodies to be encountered by the Galileo spacecraft. The objects observed were the minor planet s 951 Gaspra and 243 Ida, discussed in this paper, and the Galilean sa tellites of Jupiter, to be discussed in Paper II. Observations of Gasp ra were made from April through August 1991, and Ida was observed from 1991 November through 1993 May. Each observing campaign was followed by a successful encounter. The instrumentation, techniques, analysis m ethods, and astrometric results are described.