A Robophysical Analysis and Gait Development for the NASA Resource Prospector Rover

Planetary rovers can become entrapped in soft substrates. The LCROSS lunar mission in 2009 indicated that regolith was less consolidated at the lunar poles than the equator. This led NASA JSC to develop RP-15, a 300 kg rover capable of lifting and sweeping each wheel to develop a crawling behavior. To discover techniques to improve performance, we created a scaled (2.1 kg) robophysical rover, conducting systematic experiments in our autonomous tilting, aerating, and motion capture gantry apparatus. A combination of stepping and wheel rolling produced higher drawbar-pull than wheel rotation alone in any situation (~4x increase on a 0^o poppy incline). We validated our findings through experiments on RP-15 at JSC (~2x on a 0^o sand incline). On steeper slopes (up to 27^o, near max angle of stability), a novel gait generated forward progress via terrain remodeling via controlled avalanches. Rolling front wheels led to substrate mound formation posterior to the rover with stepping/paddling hind wheels generating forward progress; the wheel-only and walking-only gaits led to backward progress. Single paddling/rolling wheel force measurements showed a 2x increase in normal force per gait cycle over pure rolling. Our discoveries generalize to weakened (via aeration) and wet granular media.