HP³'s core component is a so-called instrumented electromechanical "mole" equipped with active and passive instrumentation for heat flow measurement (TEM-A and TEM-P) and a combined accelerometer and inclinometer (STATIL), which penetrates the ground through an internal percussion mechanism. The thermal probes are located on a 5-meter-long ribbon cable called "Science Tether", which is designed to measure the temperature and gradient down to this depth. The "Landing and Exploration Technology" and "Mechanics & Thermal Systems" departments at DLR Bremen were involved in the project.
The instrument can carry out measurements to clarify a number of important questions in planetary science, such as the development of past and perhaps even present habitats or the functioning of geological processes. Before the redefinition of the Exomars mission in early 2009, which led to the deletion of all geophysical experiments, HP3 was part of the so-called Humboldt payload. In the 2012 NASA Discovery Program decision, the Mole was selected as a payload for the InSight mission. There are also other possible uses, such as on the moon (International Lunar Networks, etc.). The successful launch of the mission took place on May 5, 2018 and the successful landing took place on November 26 of this year. The "Mole" will be set down on the surface of Mars in February 2019 and begin its work.
The Mole is based on the "PLUTO" Mole (PLanetary Underground Tool) developed by DLR for the Beagle-2 mission and delivers the forward motion of the Mole + "Science Tether" system into the ground by means of an internal percussion mechanism. The Mole contains the active thermal probe TEM-A and STATIL, both with the necessary electronics, which are insulated against shocks during operation of the Mole by vibration isolation. The "Science Tether" is used to transfer energy and data between the holding structure of the Mole, which remains on the surface ("Support System"), and the Mole itself. Another ribbon cable ("Engineering Tether") connects the "Support System" with the Mars landing vehicle. During the descent, mainly thermal, but also mechanical properties will be measured below the surface at various depths. After reaching the final depth of 3 - 5 m, the temperature gradient along the drilling depth can be monitored over several months in order to determine the heat flow from the interior of the planet together with the measurements of the physical properties of the soil.
