Mars Science Laboratory Flyaway Guidance, Navigation, and Control System Design

This paper describes the flyaway guidance, navigation, and control system design that was successfully used during the landing of NASA's Mars Science Laboratory on Mars on 5 August 2012. One of the most challenging phases of the Mars Science Laboratory mission is the entry, descent, and landing that starts with the Mars atmospheric entry and ends with the rover Curiosity landing on Mars and the descent stage with the sky crane crashing to the surface. Because the two-way signal's communication time between Earth and Mars is about 26 min and the fact that the end-to-end entry, descent, and landing takes about 7 min, the lander must be controlled completely autonomously. At the last step of the landing, the rover is lowered to the surface by using a new sky crane, which resides on the descent stage of the lander. The sky crane slowly descends toward the Martian surface as the rover is lowered. Once the touchdown is detected, the onboard control system flies the descent stage as far away as possible from the rover. This phase of the landing is called the "flyaway." The flyaway is the last phase, and its main goals are to move the sky crane, which may contain unused propellant, to a safe distance and to avoid plume impingement on the sensitive science instruments on the rover during the flyaway maneuver. The coupled attitude and translational motion is planned, that is, rotational and translational trajectories are time profiled by the onboard guidance algorithm. The trajectories obey the control authority constraints, due to maximum torque and force, while maximizing the divert distance. These guidance trajectories are tracked by using feedback control laws that provide robustness to any model uncertainties and disturbances forces and torques. Simulation results predicted that a desirable performance would be achieved in terms of the flyaway distance and the plume avoidance. Finally, the actual landing on Mars on 5 August 2012 was extremely successful, and the results were consistent with predictions.