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R. A. Jacobson, P. G. Antreasian, J. J. Bordi, K. E. Criddle, R. Ionasescu, J. B. Jones, R. A. Mackenzie, F. J. Pelletier, W. M. Owen Jr., D. C. Roth, J. R. Stauch (JPL/CalTech), Cassini Navigation Team
Prior to the Cassini Tour of the Saturnian system Jacobson (2004 {\em AJ}\, 128, 492) determined the orbits of the Saturnian satellites and a revised Saturnian system gravity field from Earth-based astrometry and observations acquired with the Pioneer~11 and Voyager spacecraft. We have been extending that work to include additional Earth-based astrometry, Cassini Doppler tracking data, radiometric range, and optical navigation imaging. Results based on data taken through March 2005 appeared Jacobson {\em et al.} (2005 {\em BAAS} 37(2), 524). The data set contained Cassini data acquired during the Cassini close flyby of Phoebe, the January 2005 encounter with Iapetus, the February and March encounters with Enceladus, and four flybys of Titan. In this paper we report on the current status of the gravity field and orbits. We have incorporated the results from two additional Titan flybys and another close encounter with Enceladus. More importantly, however, we have included the tracking data from a series of 4 consecutive Saturn periapsis passages by Cassini. As a consequence we have significantly improved our knowledge of the Saturnian system GM and the zonal gravitional harmonics of Saturn.
The authors thank S. D. Gillam and V. Alwar (JPL) for their efforts in reducing the Cassini optical navigation data.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.