Effect of Mars atmospheric pressure on percussive excavation forces

Percussive excavation tests were performed at Earth atmospheric pressure, 101 kPa, and at Martian atmospheric pressure, 600 Pa. The experimental set-up included a replica surveyor scoop attached to a custom-built, vacuum-rated hammering system. The excavation system was attached to a six axis load cell to measure excavation forces and torques. All tests were conducted in JSC-1A soil. Comparisons were made between the Earth atmospheric test data and the Martian atmospheric test data to determine how atmospheric pressure influences the effectiveness of percussion in reducing the shear strength of JSC-1A soil during excavation. Test data showed a similar reduction profile in excavation force magnitude for various percussion test permutations at both 101 kPa and 600 Pa. For both test pressures the force reduction profile is attributed to degradation in the in situ soil dilatancy. Overall, it was observed that the baseline excavation force and penetrometer Cone Index magnitude were lower at 600 Pa than at 101 kPa. This reduction in both force measurements could be attributed to one or a combination of the following: reduction in adhesion between the tool and the soil, reduction in coefficient of friction between the tool and the soil, reduction in soil cohesion, and/or reduction in soil internal friction coefficient. From the practical stand point, reduction of excavation forces at Mars pressure directly translates to lower excavation energies on Mars.