No rover had so little gravity before

No rover has fallen from the sky yet. But that's exactly what should happen in a few years - on the Martian moon Phobos. As part of the Japanese MMX research mission (“Martian Moons eXploration”), a German-French rover will fall from a height of 50 meters onto the Martian moon in free fall.

That sounds more daring than it actually is. Because Phobos, which is only around 27 kilometers across, has only one-thousandth of the force of gravity. The research rover deployed by the MMX mother probe will not crash on the Phobos surface, but will nevertheless first do a few somersaults and then come to rest on the ground in an unpredictable position.

When designing the rover, it had to be taken into account that it can stand up on its wheels and stand up on its own from such a situation with the help of a drive system. The next step would then be to unfold the solar panels that will supply the rover with electrical energy.

The real challenge comes then. "With the MMX Rover, we are breaking new technical ground, because never before has a wheeled reconnaissance vehicle driven on a small celestial body that only has around one-thousandth the force of gravity," says Markus Grebenstein from the DLR Institute of Robotics and Mechatronics in Oberpfaffenhofen.

He is the DLR project manager for the MMX rover, which was equipped with special wheels so that it can maintain contact with the ground even in very low gravity - and not take off. Nevertheless, it will move very carefully over the Phobos surface at a speed of only a few millimeters per second.

The rover consists of a particularly light carbon structure that was built in Bremen and then delivered to the French space agency CNES in Toulouse. The rover is to be completed there by summer 2023 and, in particular, all measuring devices that are to research Phobos are to be installed. Two of these systems also come from Germany – the radiometer miniRAD and the Raman spectrometer RAX. They were built at DLR in Berlin.

The rover is equipped with two cameras that can constantly keep an eye on the wheels and the ground to be driven on. There are also two more cameras that are intended for navigation. Of course, an on-board computer, a power supply system and a radio system that enables communication with a terrestrial control center are also required. Overall, the rover will only weigh 25 kilograms.

The radiometer miniRAD will use infrared measurements to determine the surface temperature of the Martian moon. On the other hand, these measurements also allow conclusions to be drawn about the porosity of the surface material. It is interesting for the scientists to compare the porosity with that of asteroid and comet samples.

Along the rover route, RAX will determine the mineralogical composition of the Phobos surface. This could allow conclusions to be drawn about the origins of the celestial body. In particular, it is exciting to compare the mineralogy of Phobos with that of the planet Mars. Rovers have already made corresponding measurements there.

The launch of Japan's MMX spacecraft is currently scheduled for 2024 on an H-3 rocket from Japan's Tanegashima Cosmodrome. About a year later, the probe will enter an orbit around Mars. From there she will first observe the two moons Phobos and Deimos. Then it's on to Phobos, where the MMX probe is expected to drop the rover in 2027.