Hammering beneath the surface of Mars - Forensic Engineering of failures in the HP3-Mole by applying multi-body dynamics simulation

In order to gain further knowledge about the evolution of terrestrial planets in our inner solar system, NASA’s InSight Mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transfer) aims to investigate Mars’ subsurface. Therefore InSight’s HP3-Instrument (Heatflow and Physical Properties Package), developed by DLR, will measure the heat flux in Mars’ interior. In order to get the instruments down to a final depth of 5m the HP3-Mole is hammering itself below the martian surface deeper than any instrument before. To achieve this challenging goal the HP3-Mole works as a self impelling nail, driven by its inner hammering mechanism. As the achieved depths as well as the needed energy for "digging" strongly depend on the locomotion performance of the Mole, the hammering mechanism has been object to analysis and optimization using numerical multi-body models. While approaching the design limits of mass minimization and performance optimization, mechanical failure in the mechanisms drive train occurred in a later prototype of the system. Therefore the validated dynamic models originally developed to support the mission related design process are adapted and used to track the failure within the tight schedules of space missions. Using simulation-based failure tracking it was possible to identify the actual failure reason. The developed simulation-based forensic engineering approach will be explained using this example.