Over the course of a few months, the HP3 'Mole' developed by the German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt, DLR) will burrow up to five metres deep into the Red Planet to explore its inner structure. This will be the first time that a fully automatic self-hammering probe of this sort has been used. The experiment is part of the NASA InSight mission to Mars, which launched on 5 May 2018. At 13:05 CEST (04:05 local time), an Atlas 401 rocket took off from the Vandenberg Air Force Base in California carrying the probe on board. The geophysical observatory is set to land just north of the Martian equator, on the Elysium Planitia plain, on 26 November 2018, having travelled for half a year, covering almost 500 million kilometres. There the small HP3 penetrometer will hammer into the Martian surface. It will remain there for about two years, providing data about the temperature gradient in the subsurface. Scientists want to understand how the interior of Mars developed, whether it still has a hot, liquid core, and what makes the Earth so special in comparison.
"We are delighted that DLR is making a significant contribution to the NASA InSight mission with HP3 – one of the mission's main three experiments – thus playing a key role in the joint exploration of the interior of Mars," said Pascale Ehrenfreund, Chair of the DLR Executive Board, at the launch in California. Hansjörg Dittus, DLR Executive Board Member for Space Research and Technology, added: "Today's successful launch is the result of six years of outstanding collaboration between seven DLR institutes and facilities, which have made the development of this highly specialised, resource-friendly excavation technology possible."
The researchers want to get a more accurate picture of the interior of Mars, and thus decipher its past. "So far, we only have an approximate idea of the structure and properties of the core, mantle and crust of Mars, and why the dynamics of its internal development slowed down so quickly compared to those of Earth," says the Principal Investigator of the HP3 experiment Tilman Spohn of the DLR Institute of Planetary Research. "We want to examine this in greater detail by carrying out the planned measurements in the Mars soil, which will also give us a better understanding of the evolution of Earth and Earth-like planets in the Solar System and other planetary systems." DLR's HP3 experiment will measure the subsurface temperature and thermal conductivity for that very purpose. The experiment consists of a housing – referred to as the support structure – placed on the surface of Mars that holds a 40-centimetre-long hammering probe with a diameter of 27 millimetres – nicknamed 'the Mole' by the scientists. Powered by an electric hammering mechanism, it will burrow its way centimetre by centimetre into the surface of Mars over a period of several weeks.
Launch from the United States West Coast
The launch of the InSight mission southwards over the Pacific Ocean is the first time that an interplanetary probe has been launched from the United States West Coast. The spacecraft reached orbit 13 minutes and 16 seconds after launch. Seventy-nine minutes later, the Centaur ignited a second time, sending InSight on a trajectory towards the Red Planet. InSight separated from the Centaur 14 minutes later – 93 minutes after launch – and contacted the spacecraft via NASA's Deep Space Network at 14:41 CEST. Two months prior to its arrival on Mars, following further minor course corrections and a plethora of system tests, InSight will be ready to enter the Martian atmosphere at over 20,000 kilometres per hour. The lander will enter the Mars atmosphere at a shallow angle before beginning the critical landing phase (entry, descent and landing, or EDL). Once this has been accomplished, InSight will descend to the surface of the planet using a parachute, from which it will separate and be slowed down by thrusters. Contact will be maintained with the space probe during its flight to Mars and over the course of the mission itself via the 70-metre antennas of NASA’s Deep Space Network in California, Australia and Spain.
The HP3 experiment on the NASA InSight mission
The InSight mission is being conducted by the Jet Propulsion Laboratory (JPL) in Pasadena, California, on behalf of NASA's Science Mission Directorate. The InSight mission is part of the NASA Discovery Programme. DLR is contributing to the mission with its HP3 (Heat Flow and Physical Properties Package) experiment. The DLR Institute of Planetary Research, which was responsible for developing the experiment in collaboration with the DLR institutes of Space Systems, Optical Sensor Systems, Space Operations and Astronaut Training, Composite Structures and Adaptive Systems, System Dynamics and Control, and Robotics and Mechatronics, is leading the experiment. The industry partners Astronika, CBK Space Research Centre, Magson and Sonaca are also involved. The Space Research Institute at the Austrian Academy of Science and the University of Kaiserslautern are scientific partners for the project. HP3 is operated by the DLR Microgravity User Support Centre (MUSC) in Cologne.
Detailed information on InSight and the HP3 experiment are available in this background article and on DLR's dedicated mission site: www.dlr.de/en/insight