23 Jul 2024


Motor-driven probe will drill into Mars’ history

The lander's “Mole” probe is using a motor-driven, spring-loaded rod to drag sensors up to 5m below the surface.

Nasa’s InSight probe, which landed on Mars in November 2018, is using a motor-driven probe to penetrate 5m into the Martian surface to shed light on the formation of rocky planets. The lander is scheduled to perform measurements for the next two years that will provide insights into Mars and the formation of the Earth.

The HP3 probe, developed by the German Aerospace Centre, will determine the planet’s temperature profile. A rod-shaped penetrometer, nicknamed “the Mole”, will be driven 5m into the Martian surface.

This will be done using a 22mm-diameter motor-gearhead to tension a spring. The spring will then be released, producing a powerful downward punch. In this way, the Mole will burrow downwards over a period of several weeks, pulling a cable equipped with sensors as it moves to determine the thermal state of the interior of Mars and to help researchers draw conclusions about the planet’s origin. Because Mars is a rocky planet like the Earth, the results may also help to gain a better understanding of our own planet.

To drive the penetrometer, the DC motor will need to withstand forces of more than 400 g at least 100,000 times. The motor was developed for the mission by the Swiss manufacturer maxon motor, and it took several variations and failed tests before it came up with a suitable design. The motor is based on a standard DCX 22 motor, modified by the addition of welding rings, bearing welds and specially shortened brushes. The only change needed to the attached GP 22 HD gearhead was to fill it with Mars-specific lubrication.

The InSight probe is being powered by two solar panels. To save costs, the Jet Propulsion Laboratory (which is conducting the mission for Nasa) re-used designs from its earlier Phoenix mission. Another maxon DC motor being used to extend the panels. This motor (an RE 25) has helped to keep Nasa’s Opportunity rover active on Mars for more than 14 years (although it is currently in deep sleep due to a sandstorm).