THE CASSINI MISSION AT SATURN

摘要

The Cassini Mission to Saturn, a joint undertaking by NASA, the European Space Agency, and the Italian Space Agency, is now at about the mid-point of its planned four year tour of the Saturnian system. Close encounters with Titan and the smaller icy satellites are occurring on schedule, and observations of these bodies along with Saturn's atmosphere, its rings, and magnetosphere are being made and scientific data returned on a daily basis. The icy satellites are turning out to be more distinct and unique than had been anticipated, the dynamics of the ring particles have been shown to be even more extensive than expected, and Titan's atmosphere had surprises for both the scientists as well as the engineers. A denser than expected upper atmosphere on Titan has led to the requirement to modify the planned orbital tour about Saturn to increase the flyby altitudes for about 20 of the Titan flybys to values above the originally planned 950 km level in order to avoid the risk of atmospherically induced torques causing the spacecraft to be unable to maintain its commanded attitude. Navigation of the spacecraft on the tour continues to go exceptionally well, with optical navigation enabling delivery accuracies to some of the satellites down to the one or two kilometer level, and propellant consumption is running slightly below budget. Science observation sequence development and execution has been highly successful in acquiring virtually ail of the originally designed observations. This paper summarizes the supporting engineering activities over the past year in support of operating the mission, as well as provides a high level summary of the scientific results of the Cassini mission to date.