To learn more about Mars and its structure, NASA sent the robotic probe InSight that landed in November 2018. Now it’s time to find out how much heat is escaping Mars’s interior. This will be done with an instrument called HP3 that will enter five meters deep into the ground. It is a bolt, lovingly dubbed “Mole” by its developers. It works like a nail that drives itself into the ground.
Inside the Mole, there is a maxon-built drive, consisting of a DCX 22 motor and a GP 22 HD planetary gearhead, that has to stand up to extremely high requirements. This is because Mars, with its temperature fluctuations, sand storms, and thin atmosphere, is a very unfriendly place for technology. On top of that, the brushed DC motor is going to be exposed to forces of up to 400 g. The motor’s task is to wind up a spring, which then releases with great force, executing a powerful downwards punch. This causes the bolt to drive itself into the ground step by step. The whole process takes several days. Once embedded, the device stays in place.
The measurement is performed using a cable equipped with temperature sensors dragged along by the Mole. It is used to generate an exact temperature profile of the ground on Mars over a two-year period, to determine the surface heat flow. Information on the porosity and density of the ground can also be derived from the penetration speed of the Mole. Both results are of great interest for terrestrial geophysics and will give us a better understanding of the formation and evolution of rocky planets.