Saturn Impact Trajectories for Cassini End-of-Mission

Potential end-of-mission scenarios to be considered for the Cassini spacecraft must satisfy planetary quarantine requirements designed to prevent contamination of a pristine environment, which could include Titan and the other Saturnian moons. One assumed acceptable option for safe,disposal of the spacecraft includes Saturn impact trajectories. Two classes of impact trajectories are investigated: short-period orbits characterized by periods of 610 days and long-period orbits with period, greater than 850 days. To impact Saturn with short-period orbits, a series of successive Titan flybys is required to increase inclination and decrease periapsis to within Saturn's atmosphere, while simultaneously avoiding the rings and mitigating Delta V expenditures. To ensure that the spacecraft is not prematurely damaged by material in the rings, Tisser and graphs are employed to determine when the ring-plane crossing distance is within the F-G ring gap: the necessary geometry for the penultimate transfer. For long-period Impact trajectories, solar gravity is exploited to significantly lower periapsis. Depending on the size and orientation or the long-period orbit, a maneuver (<50 m/s) at apoapsis must be added to ensure impact. For sufficiently large orbits with favorable characteristics, solar gravity alone drops the spacecraft's periapsis into Saturn's atmosphere. No maneuver is necessary after the final Titan flyby, providing an attractive flyby-and-forget option.