I, ‘! ’.* An Attitude Control Design for the Cassini Spacecraft

The Cassini planetary mission to Saturn and Titan requires accurate pointing and complex maneuvers of the spacecraft, which is comprised of a Saturn orbiter and Titan probe. An attitude control design is described to achieve the many capabilities of Cassini including thrust vector control, precision pointing and stability control fc)r remote sciences, tracking of a probe released to the Titan atmosphere, and radar mapping of the Titan surface. Additional constraints for control design have been imposed by a high percentage of liquid propellant (60. % at launch) and lowly damped flexible spacecraft appendages. Computer simulation results of attitude determination, pointing and maneuver controls are provided to demonstrate the design capability. I 1. IntroductionI 1.1 Mission and Science Objectives The Cassini spacecraft to Saturn and Titan is scheduled for launch in 1997, and will arrive at Saturn in 2004. It will orbit the inner solar system to pick up Venus and l;arth gravity assists, followed by Jupiter flyby and Saturn orbit insertion. Probe entry to the atmosphere of Titan will occur about four months after Saturn arrival. Unlike both Voyager 1 and 2 which flew by Saturn but did not go into orbit