Percussive Penetration of Unconsolidated Granular Media in a Laboratory Setting
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This controlled study examined the feasibility of a simple percussive approach to drilling through unconsolidated regolith deposits on Mars. The experiments showed that the approach is feasible at the low power levels and low confining pressures used, and that the rate of impact is more important to the penetration rate than is the mass of the impactor (hammer). More massive impactors tend to lower energy efficiency, as they do in terrestrial pile-driving. Unexpectedly, penetration plotted against applied energy tends to cluster into parallel linear trends. Within a given cluster, penetration is very sensitive to applied energy, while between clusters, the same penetration requires different energy levels. The clusters are separated by gaps whose widths may be related to the average grain size of the material being penetrated. The layered nature of natural sedimentary deposits is reflected in the cumulative energy-penetration plots, which could thus serve to record bedding thickness and frequency during Mars exploration. This study has shown that percussive drilling using a down-the-hole hammer design may be feasible in unconsolidated fine regolith near the ground surface.