Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21715601j&link_type=abstract
American Astronomical Society, AAS Meeting #217, #156.01; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
We have carried our a series of Very Long Baseline Array (VLBA) astrometric observation of the Cassini spacecraft, which is currently orbiting Saturn, to determine the position of Saturn's center of mass in the International Celestial Reference Frame (ICRF). Our positional accuracies are typically 0.2-0.3 milli-arcseconds, corresponding to about 2 km at the distance of Saturn. The goal of the project is to improve the Saturn ephemeris. This paper reports the results of our first eight epochs of observing, from October 2006 through April 2009. A new planetary ephemeris (DE 422) has been fit to these data, plus two earlier VLBA observations of Cassini by others and a Cassini-based VLBA gravitational deflection experiment by Fomalont et al. in February 2009. Post-fit residuals for DE 422 have a mean offset less than 0.2 mas in both coordinates, but not all of our phase reference sources have ICRF position with this accuracy yet. Future observations will improve reference source positions, and will continue to follow Saturn through more than 1/4 of its orbital period. (The Cassini mission is currently funded to operate until 2017.) We are grateful to Larry Teitelbaum for support of this project through the Advanced Tracking and Observational Techniques of JPL's Interplanetary Network Directorate, and to John Benson and the VLBA operations team at NRAO for their excellent support of these observations. The VLBA is a facility of the National Radio Astronomy Observatory, which is operated by Associated Universities, Inc., under a cooperative agreement with the National Science Foundation. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
Border Jamess.
Dhawan Vivek
Folkner William
Fomalont Ed
Jacobson Robert
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