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A. Kliore, N. Rappaport, A. Anabtawi, S. Asmar, J. Armstrong, E. Barbinis, G. Goltz, D. Johnston, D. Fleischman, D. Rochblatt, J. Anderson (JPL), E. Marouf, K. Wong (SJSU), F. Thomson (Stanford U.), F. M. Flasar, P. Schinder (NASA-GSFC), R. French, C. McGhee (Wellesley Coll), P. Mohammed, P. Steffes (GIT), A. Nagy (U. Michigan), L. Iess (U. Roma), P. Tortora (U. Bologna), R. Ambrosini (IRA-CNR), E. Flamini (ASI)
The Cassini spacecraft, which has been in orbit about Saturn for over a year, is the first Radio Science platform to provide three downlink frequencies. In addition to the X-band telemetry link (3,56 cm w.l.), two other frequencies, S-band (13.04 cm), and Ka-band (0.94 cm) are available. This, plus the high SNR (>50 dBHz at X-band) afforded by the 4 m diameter s/c high gain antenna in combination with the excellent low noise receivers of the DSN, as well as overall system stabilities of 1 x 10-13 when referenced to the on-board ultra-stable oscillator (USO) in one-way operation, and 1 x 10-15 for a two-way link, make Cassini an unprecedented instrument of radio science.
In addition to Gravitational Wave Search and Solar Conjunction experiments conducted during the cruise phase, the orbital tour phase of the mission has as its main radio science objectives:
a) determination of the masses and gravity fields of Saturn's icy satellites, Titan, and Saturn through two-way tracking during fly-bys. To date, the masses of Phoebe, Iapetus, Dione and Enceladus have been measured, and will be reported here.
b) Measurement of the structure and other properties of Saturn’s rings through three-band occultation. Several near-diametric occultations at a high ring opening angle have been completed, and the results will be presented here.
c) Measurement of the vertical structure of the atmosphere and ionosphere of Saturn. The same series of occultations have provided nearly equatorial occultations, and the results on the atmosphere structure, the ionosphere, and the abundances of microwave-absorbing gases in Saturn's atmosphere will be described here.
In the remaining years of the Cassini mission, these results will be expanded to include the atmosphere, ionosphere, surface, and gravity field of Titan, the gravity field and masses of Saturn and the remaining icy satellites, and the completion of the Saturn objectives described above.
The Cassini Radio Science Team wishes to express its gratitude to the personnel of the DSN, whose contributions have made our results possible.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.