Pointing-Stability Performance of the Cassini Spacecraft

The operations of Cassini optical remote sensing instruments require a high level of spacecraft-pointing stability to minimize image distortion during an exposure window. This paper summarizes the flight performance of the Cassini spacecraft's pointing stability with respect to mission requirements. Sources of spacecraft jitter, the Cassini spacecraft control modes, and pointing-stability metrics are discussed to provide a context for the results. In designing the Cassini attitude-control system, a pointing-stability performance metric that considered the frequency contents of the disturbance sources was employed. Cassini pointing-stability results using the root-mean-square stability metric are provided for both spacecraft control modes, using the reaction-wheel assembly or the reaction control system composed of eight thrusters. The pointing-stability results are then related to characteristics of the spacecraft and operations. For thruster-based control, the pointing-stability results are analyzed with respect to the per-axis dead band. Results from the scientific instruments onboard the Cassini spacecraft confirm that the pointing-stability results in either control mode have achieved high accuracy pointing capabilities critical to the success of the mission and have resulted in data to improve our understanding of Saturn. [PUBLISHER ABSTRACT]