Interest in robotic subsurface investigations has been growing internationally. So far, the development of devices for sampling and analyzing the Martian subsoil has particularly progressed. Currently, the detailed investigation regarding the interior of the Moon is notable. Hence, implementation of subsurface exploration technology is required. This paper presents a lunar subsurface explorer that can burrow by itself in order to bury a scientific instrument such as a long-period seismometer. For the development of this drilling and self-propelled robotic explorer, the authors first discuss qualitatively its locomotion strategies and then focuses on a conical screw drilling mechanism taking into account the lunar soil properties. More specifically, this paper presents a novel screw drilling mechanism, called the CSD (contra-rotor screw drill), which mainly consists of a front and a contra rear screw. The proposed mechanism also has a structure that exerts no reaction against the body and has the capability to agitate compacted soil. The performance of the CSD is evaluated by indexes based on kinematic states and dynamic inputs. The validity is confirmed by comparing the experimental results of the fundamental screw drill, called the SSD (single screw drill). The main contribution of this paper is to investigate the feasibility of screw drilling applied to the lunar subsurface explorer and to examine the possibility to realize an effective drilling condition of the CSD.
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