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R.C. Stone (USNO, Flagstaff Station)
For the first time, the Hipparcos and densified versions thereof (Tycho and ACT) catalogs of star positions provide a highly accurate optical reference frame that can be used with differential CCD reductions to determine accurate positions for solar system objects. This paper describes the observing program that started in 1998 with the Flagstaff Astrometric Scanning Transit Telescope (FASTT) to significantly improve the ephemerides for the outer planets, many of their satellites, and a large number of asteroids and comets. All of the FASTT observations are reduced to J2000 (ICRS) equatorial coordinates using differential reductions with reference stars taken from the ACT star catalog, and accuracies of ±60 mas in each coordinate are routinely achieved. The current FASTT observing program includes three planets (Uranus, Neptune, and Pluto), 18 satellites of Jupiter, Saturn, Uranus, and Neptune, over 2000 asteroids, and various targets of opportunity. These data are being used for a variety of projects, such as to improve the ephemerides of solar system targets prior to spacecraft encounters (NEAR, DS1, Cassini, and Pluto Express), compute dynamical masses for asteroids, provide accurate predictions for occultation events, and to investigate the dynamics of asteroids and various planetary satellite systems. Over 30 thousand observations were taken in the past year, and this observing program will continue.
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