To unravel planets' histories and discover new resources, researchers have undertaken various planetary investigations. In particular, subsurface investigations will play an important role in both elucidating the origins of extraterrestrial bodies and developing planetary workstations. To put these investigations into practice, we have been developing a lunar subsurface excavation robot using peristaltic crawling based on an earthworm's locomotion. This robot comprises three units: a propulsion unit, an excavation unit, and a discharging unit. In our previous research, we demonstrated the potential of this robot with the propulsion and excavation units. In this paper, we first show the excavation performance of the robot with three units for propulsion, excavation, and discharging. Result of this excavation elucidates the problem that the soil dropping from the discharging unit interrupts the robot's excavation. To overcome this problem, we propose a “soil-circulating system”. Moreover, we conduct verification experiments for realization of the system. Finally, we conduct an excavation experiment with the robot, which incorporates the system. The experimental results validate the proposed system.
