Guidance with Supersonic Retropropulsion for Mars Pinpoint Landing

摘要

Future human and robotic missions to Mars require the landing of heavier payloads with greater precision. The present entry, descent and landing (EDL) technology is that of the Viking mission with necessary modifications. But this will be challenged by the larger payload mass of the future missions. The high ballistic coefficient of such missions makes parachute deployment impractical. The spacecraft will reach the parachute deployment conditions only at a low altitude with insufficient time for the rest of the EDL events. Also the diameter of the parachute has to be increased and materials which can withstand the atmospheric conditions must be used. This will demand new qualification methods to test the performance of the parachutes. One of the technologies that can be used as an alternative is Supersonic Retropropulsion (SRP). SRP uses thrusters to decelerate the spacecraft to safe landing velocities. Two distinct guidance algorithms to be used in the supersonic regime are discussed in this paper: a minimum time optimal guidance and a polynomial guidance. The optimal thrust angle required to be maintained in the supersonic phase is obtained using calculus of variations. In the subsonic phase, the vehicle uses polynomial guidance to decelerate to safe landing velocities.