Abstract
After nearly a seven years flight, mother and daughter spacecraft, Cassini-Huygens, entered into Saturn orbit on July 1, 2004. They parted ways on December 25, 2004 on a trajectory that sent Huygens on a rendezvous with Titan (Saturn's planet-size satellite) on January 14, 2005. Data collected during a 2 hours 32 minutes descent in Titan's thick atmosphere and a surprising 1 hour 12 minutes on its frigid surface promise to provide critical pieces of information regarding the physical nature of this enigmatic satellite. Meanwhile, the mother orbiter Cassini continues on its planned "tour" of the Saturn system, completing 74 revolutions around Saturn by June 30, 2008 (the nominal mission lifetime). The orbits have been designed to provide balanced integrated science from a set of 12 major Cassini instruments that observe Saturn, its ring system, its particles and fields environment, and many of its satellites (including 44 close-encounters with Titan). Some of the early orbits have already provided much useful data. One of the 12 Cassini instruments is the Radio Science Subsystem (RSS) designed to investigate physical properties and structure of Saturn's rings, the atmospheres and ionospheres of Saturn and Titan, and to determine the mass and gravitational harmonics of Saturn, Titan, and other major satellites. The radio observations are conducted using three nearly monochromatic coherent signals (0.94, 3.6, and 13 cm-wavelength; Ka-, X-, and S-Band, respectively), a capability unique to Cassini. Here, radio occultation observations of Saturn's rings are used as an example to illustrate expected performance from a set of eight optimized Cassini orbits to be implemented during the period May to September 2005. The expected performance is contrasted with the 1980 Voyager ring occultation and with a target-of-opportunity X-band only ring occultation conducted during Saturn orbit insertion using the Cassini low-gain antenna. Despite the much lower free-space SNR compared with nominal experiments using the high-gain antenna (~10 dB compared with ~50 dB, or a factor of ~10,000 less), the signal was detectable over most ring features, except for the thick Ring B. Preliminary results are presented.