Design details of the HP3 mole onboard the InSight mission

Abstract

The HP³ Mole system is part of the HP³ payload on the InSight discovery class mission, which will place a geophysical lander onto the surface of Mars in 2018. DLR's HP³ - instrument (Heat Flow and Physical Properties Package) will measure Mars' interior heat flux and thermal gradient down to a depth of 5 m and thus penetrates deeper below the Martian surface than any other instrument before. Being the locomotion system of the instrument, the HP³ Mole acts as a self-impelling nail in order to accomplish this goal. The inner hammering mechanism is spring driven and periodically loaded by a cylindrical cam mechanism. The innovative impact driven locomotion principle enables a minimum in required energy and mass, but leads to complex system behaviour and dependence of the inner mechanism dynamics on the outer force conditions exerted by the soil. The scope of this paper is to provide an overview of the Mole, its role in the mission and payload, as well as to give a brief overview about its subsystems, its interfaces and working principle.