Astrometry for the Galileo Mission. I. Asteroid Encounters

Optical Charge Coupled Device (CCD) astrometry was done at the U.S. Naval Observatory Flagstaff Station (NOFS) to obtain positions of solar system bodies to be encountered by the Galileo spacecraft. The objects observed were the minor planets 951 Gaspra and 243 Ida, discussed in this paper, and the Galilean satellites of Jupiter, to be discussed in Paper II. Observations of Gaspra 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 methods, and astrometric results are described.