Hammering beneath the surface of Mars – Modeling and simulation of the impact-driven locomotion of the HP3-Mole by coupling enhanced multi-body dynamics and discrete element method

As the formation of the rocky planets in our inner solar system has always been a major subject of scientific interest, NASA’s discovery mission InSight (Interior Seismic Investigations, Geodesy and Heat Transport) intends to gain further knowledge about the interior structure of Mars. In order to understand the processes that lead to planetary evolution, Mars’ seismic as well as thermal properties will be measured. DLR’s HP3-Mole (Heat Flow and Physical Properties Package), an innovative self impelling nail, will hammer itself into the red planet deeper than any other instrument before, in order to measure the heat flux and thermal gradient down to a final depth of 5 m. To achieve this challenging goal, high fidelity simulation models have been used throughout the whole development process. To meet the demands on accuracy, two detailed models were created based on enhanced multi-body dynamics and discrete element techniques. For the most detailed analysis both methods are coupled to enable further understanding of the interaction between Mole mechanism and soil dynamics. Validation has been carried out for every existing prototype stage of the mechanism and has shown very good correlation between measurement and simulation. Additionally the soil model is compared to penetration tests in real soil as well as cone penetrometer measurements. Using these simulation models various influences can be evaluated by virtual prototypes in the actual environmental conditions of Mars, which would not be achieved in reality before the start of the mission. By supporting the design with detailed simulations, it was possible to increase the locomotion performance while reducing the consumed power remarkably, i.e. by less than 5W of input power