Dual Reciprocating Drilling in Planetary Regoliths: Evolution of a Bio-Inspired Solution.

To find life on Moon, Mars or other space bodies, drilling capabilities are required. Whether it be to take a sample or to conduct in-situ experiments, drilling increases the scientific return of any space exploration mission. However, high constraints on a space systems’ mass and low gravity environments lower the performance of rotary drilling (massively used on Earth for oil, gas and mining). A novel solution was identified in the manner the wood-wasp (a 1 cm-long insect) drills into wood to lay its eggs. Previous research and publications suggested that by imitating this insect, one could develop a planetary drill requiring no normal force or external push to progress. Such a system could enable drilling and sampling from highly miniaturized probes. This thesis builds on this concept and explores the feasibility and performance of such a bio-inspired drilling solution in regoliths, the loose granular material that covers the surface of the Moon and Mars. This bio-inspired drilling mechanism is named Dual Reciprocating Drilling (DRD). To enable engineers to design a compact and efficient DRD system, it is necessary to understand and characterize the interaction between the drill head and the regolith surrounding it. At the start of this research the understanding of DRD did not allow to chose between different DRD system architectures. The main focus of the PhD was thus laid on testing and understanding the behaviour of the drill head in the regolith. The novelty of DRD in regoliths and the high preference for experimental approaches in soil mechanics, drilling and space exploration has pushed this research to adopt a predominantly experimental approach (though some numerical and analytical modelling has been contributed). Four major steps were taken to enhance our understanding of DRD in regolith. First Moon and Mars regolith simulants were identified and characterized. Their geotechnical properties were experimentally obtained. Special emphasis was laid on the manner they were prepared. Preparation methods were proposed and tested. Secondly, a custom test bench was built to test DRD in the regolith simulants. This allowed to identify the importance of slippage in the drilling process for the first time (concept taken from vehicle traction and adapted for DRD) and to propose DRD penetration mechanics in regolith. Then to confirm the first experimental results, a simplified force sensor test bench was built. It was used to measure the influence of slippage on the forces between regolith and the DRD. This allowed to revise and confirm the DRD penetration mechanics proposed previously. The importance of lateral movements during the drilling process was identified. Finally, to enable future regolith drill developers to have a numerical simulation tool, the recent advances in hardware computing (Graphics Processing Unit (GPU)) were used to conduct the first very large number of particles numerical simulations of regolith drill interaction (using discrete element methods). This allowed to confirm the importance of lateral forces in DRD. To conclude, the work presented in this thesis has lead to a significant advancement of our understanding of the manner DRD is considered. Before this work, it was considered as able to generate its own drilling force. In regoliths it is now clear that it requires non-zero external force to drill. However it does enable to lower this drilling force (thanks to lateral forces and displacements) making it an efficient solution to be considered for future planetary exploration. A system architecture reflecting this new vision of DRD is proposed