15 Rover-Years of Slip Risk Assessment for Robotic Arm Safety

Science return from the Curiosity and Perseverance Mars rovers, like Spirit and Opportunity before them, depends in large part on “contact science” activities in which instruments on a turret mounted on a robotic arm are placed near, on, or into the ground surface. When planning arm operations, rover teams are responsible for ensuring that torques and forces on arm joints and links will not exceed design specifications during contact science. This necessarily includes consideration of likelihood and consequence of rover movement due to wheel slip or settling. Simulation tools and practices for protecting Curiosity's arm were initially presented at this conference by [1], centered on the Slip Risk Assessment Process (SRAP). During the 12 Earth years of operating Curiosity and 3 years of operating Perseverance (“15 rover-years”), SRAP and related arm safety procedures were gradually improved, and subsequently adapted for use on Perseverance operations. Herein, we summarize those improvements and adaptations and then examine the use of SRAP and related procedures since their inception. We present data addressing questions including: How often do arm safety concerns preclude arm contact science? When contact science is precluded, what are the primary scenarios of concern? What is SRAP's impact on the planning timeline? How do predicted wheel slip likelihoods compare with observed slip event frequency? In discussing these questions, we aim to consider how the Curiosity and Perseverance arm safety paradigm might be further optimized to maximize science return while maintaining hardware safety. We also aim to provide lessons that may be of use to planetary missions conducting terrain-contact science, including upcoming Lunar missions.