Target effects during penetrator emplacement: heating, triboelectric charging, and mechanical disruption

The violent emplacement of penetrators has effects on the target material which, while largely ignored to date, may be quite significant in the interpretation of scientific data returned from penetrators or may even cause system failures. These effects, for which we offer preliminary quantification, include heating of the target material, largely but not exclusively by frictional heating along the walls of the penetrator, the development of triboelectric charge, and the mechanical compaction, comminution and fracturing of the target material. The sparse and often difficult-to-obtain literature on these processes is summarized, and some unique preliminary experiments conducted in support of the NASA DS-2 Mars Microprobe mission are reported. We urge future spacecraft penetrator projects to pay attention to these interesting and important phenomena.