Earthworm-inspired subsurface penetration probe for landed planetary exploration

Terrestrial subsurface exploration equipment has developed over time to take advantage of the planet’s gravitational acceleration and energy availability. Today, heavy surface equipment provides the reaction forces needed to overcome the ground penetration resistance. Energy is so readily available that the depth-limiting parameter is often the surface anchor weight. To access the lunar subsurface, mankind will need to overcome its low gravity environment with a limited power supply. This paper reports on the performance of an earthworm-inspired subsurface penetration probe developed to mimic the annelid’s anterior end. The device can be described as a miniature cone penetration probe equipped with a soft membrane that is actuated by an external hydraulic system. Subsurface penetration tests are conducted using lunar mare simulant at high void ratio. The results show up to 80% reduction in penetration resistance at a maximum peak power demand of 0.2 watts. Moreover, the penetration resistance, penetration energy, and power demand can all be adjusted by tuning the probe inflation volume and penetration depth interval. Thus, the earthworm-inspired penetration process can be adapted ‘on the flight’ to site-specific conditions.