MSL CRUISE ATTITUDE CONTROL FLIGHT EXPERIENCE AND IMPLICATIONS FOR MARS 2020

The spectacular landing of the Mars Science Laboratory "Curiosity" rover in August 2012 was made possible by the near perfect delivery of the vehicle to the planned entry conditions after a 8-month interplanetary cruise. Using a spin-stabilized attitude control architecture based on the earlier Mars Exploration Rovers and Mars Pathfinder missions, MSL executed 4 trajectory corrections, 22 turns to maintain power and communications and 18 turns in support of in-flight alignments and calibrations. To enable use of a guided, lifting entry, cruise ACS was also called on to perform a high-reliability precision initialization of the entry vehicle's onboard inertial navigation system just before landing. Along with other surprises, cruise operations were complicated by an early problem with the spacecraft flight computer which prevented use of the onboard star scanner for the first few months of flight. During this important period, ACS activities were accomplished using a combination of sun-only modes and ground based attitude determination. This paper outlines the MSL cruise attitude control system and relates our flight experience during operations, describing some of the challenges faced during the mission and the techniques and system features used to over-come them. We also present a performance assessment and several lessons learned with relevance. to Mars 2020 and other future missions using the MPF/MER/MSL cruise architecture.