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[15.02] The Orbits of the Major Saturnian Satellites and the Gravity Field of the Saturnian System

R. A. Jacobson, P. G. Antreasian, J. J. Bordi, K. E. Criddle, R. Ionasescu, J. B. Jones, M. C. Meek, W. M. Owen Jr., D. C. Roth, I. M. Roundhill, J. R. Stauch (JPL/Caltech), Cassini Navigation Team

In preparation for the Cassini Tour of the Saturnian system Jacobson (2004 {\em AJ}\, 128, 492) developed ephemerides for the Saturnian satellites based on numerical integrations of their orbits fit to Earth-based astrometry and observations acquired with the Pioneer~11 and Voyager spacecraft. A byproduct of this effort was a revised Saturnian system gravity field. We have extended this work to include Cassini Doppler tracking data, radiometric range, and optical navigation imaging. We find significant corrections to the orbits of Mimas, Enceladus, Hyperion, Iapetus, Phoebe, Helene, Telesto, and Calypso. Changes in the gravity field, however, are minimal with the exception of the GM of Phoebe. Analysis of data from the Cassini 2070 km altitude flyby of Phoebe leads to a value of 0.5527\,±,0.0010 km³ s^-2 for the Phoebe GM.

The refinement of the satellite orbits will continue throughout the Cassini tour. Planned low altitude flybys of Enceladus, Dione, Rhea, Titan, Hyperion, and Iapetus will permit improvement in the knowledge of their GMs.

The authors thank S. D. Gillam and T-C. M. Wang (JPL) for their efforts in reducing the Cassini optical navigation data.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.