IDEFIX, the first spacecraft to tour Phobos, the largest moon on Mars

Next year, Japan will send the MMX probe to Mars (Exploration of the moons of Mars), an ambitious mission aimed at returning surface samples from Mars’ largest moon, Phobos. The probe is carrying a very special passenger: a European rover that will explore the surface of Phobos. The rover, which was conceived in 2019 and is in the final stages of its construction, has just been named IDEFIX. In fact, the name refers to the famous puppy from the Asterix comics – although we remember that the dog belongs to Obelix – which in French sounds like fixed idea (“Permanent Idea”). Until now, IDEFIX was simply called MMX Rover (MMX ロ ー バ in Japanese), so this is definitely a good decision (IDEFIX is translated in Japanese as Hiramiki閃き, “inspiration”).

IDEFIX will be the first wheeled vehicle to move through a low-gravity object (thousandth of a g). This is a project led by the French and German space agencies (DLR and CNES) in collaboration with the Japanese space agency JAXA and the Japanese universities in Tokyo and Rikkyu. It will also have significant Spanish participation through INTA (National Institute of Aeronautical Technology) and the University of Valladolid (UVa). IDEFIX builds on cooperation between Japan, France and Germany when developing the “Rover” mask (Surface mobile asteroid sCOuT), which landed on the asteroid Ryugu in 2018 after traveling there on the Japanese probe Hayabusa2.

IDEFIX has a mass of 25 kg and a height of 41.5 cm, with dimensions of 44 x 52 x 35 cm in its compact configuration. Each wheel has its own electric motor. It will launch next year to Mars with the MMX probe (火星衛星探査機 in Japanese) and land on Phobos in 2027. Its mission will last about 100 days, during which it will travel a maximum of several hundred meters. And it is that IDEFIX will only move at a very, very slow speed, 0.1 to 4 millimeters per second, approximately (average speed would be 1 to 2 mm/sec). This slowness is mainly due to the difficulty of moving in a low-gravity environment. The gravitational acceleration on Phobos ranges from 0.004 to 0.007 m/s2 and varies a lot because this moon of Mars is not spherical in shape. If one thinks about it, the amazing thing is that a satellite 27 kilometers long generates such “intense” gravity. Maintaining a grip on the regolith won’t be easy, but the engineers at DLR and CNES believe wheels are a better option than jumping mechanisms like the ones MASCOT uses. In this sense, it is worth remembering that IDEFIX is not the first probe designed to study the surface of Phobos.

In the late 1980s, the Soviet probes Phobos 1 and Phobos 2 both carried sub-probes to explore the surface of Phobos. One of them was a stationary surface station, called DAS (Долговременная Автономная Станция, “long-duration autonomous station”), weighing 67 kilograms, intended, like IDEFIX, to last about 100 days and which was supposed to use a harpoon to stick itself into the regolith of Phobos (like the Philae probe). European on Comet 67P). The other probe was the small robot PrOP-F —PROP-Ф (Прибор Оценki Проходимости, ‘Device for Evaluation of Mobility on Phobos’) – weighing 50 kg, equipped with four arms, two of which are ambulatory, which will have jumps of 20 meters in length allowed . Unlike the DAS, which had three solar panels, the ProOP-F used batteries, so its useful life was limited to 4 hours. Because of this, only about ten jumps are planned. The Phobos 1 probe carried a DAS terminal, while Phobos 2 carried DAS and PrOP-F. Unfortunately, Phobos 1 got lost on its way to Mars and Phobos 2 failed in April 1989 shortly before the Phobos investigation began. As a curiosity, France took part in equipping the DAS station for the Phobos probes with a CCD camera and a solar sensor, so we can say that the French state once again tried to land on the largest moon of Mars, after four decades.

Engineers at NPO Lavochkin and the Soviet IKI considered that in the low-gravity situation of Phobos a jumping rover would be ideal, but CNES and DLR believe they have solved all the problems of a wheeled rover, including skidding – if the wheels don’t have enough grip -, or sudden changes in position that could cause the wheels to collide with each other or with the solar panels. IDEFIX includes two scientific instruments, in charge of the DLR, to study the composition and thermal properties of the surface of Phobos: the Raman spectrometer RAX (Raman spectrometer for MMX), with Spanish participation, and the miniRAD radiometer. It also carries two navigation cameras provided by the French National Center for Space Studies and two other cameras (WheelCams) to monitor the wheels (studying the effects of wheels on the soil is a scientific experiment in itself). The communication system with an MMX probe – IDEFIX will not be able to communicate directly with Earth – is also responsible for CNES, which also built the IDEFIX central service unit with a vehicle computer. For its part, DLR directs the construction of the rover’s wheels, chassis and motion system, as well as the MMX probe communication system.

After launch, IDEFIX will have two control centers, one in Toulouse and one in Cologne. MMX IDEFIX will fall with the wheels folded, causing them to open up on the surface in such a way that they can be held in the correct position even if they fall upside down. Being a solar-powered rover, it has to move to make sure the sun lights up the panels, which is why the SKA system exists (Le Systeme für die Controlle of the Attitude, yes, mixing German, French and English) to properly orient the rover based on the BiSo-64 sun sensor (IDEFIX does not carry an inertial navigation unit). The solar sensor will determine the rover’s orientation with respect to the sun with an accuracy of 0.1 degrees. IDEFIX has just completed thermal and vacuum resistance tests in Toulouse. Its construction will be completed this summer and it will leave in September for Japan. If all goes well, in 2027 it will orbit Phobos for about three months. For its part, the MMX probe should return in 2029 with samples from the surface of Phobos, samples that it must collect with a robotic arm, a peculiarity that distinguishes it from the Japanese Hayabusa probe or NASA’s OSIRIS-REx.

MMX will land on Phobos in an area previously analyzed by IDEFIX using a quadrupedal lander. Although it would certainly be amazing to see Mars from the surface of Phobos, IDEFIX will land in the opposite hemisphere, where the Red Planet is not visible, in order to facilitate communications between MMX and Earth and to simplify lighting conditions. MMX will orbit Phobos and pass Deimos, studying both satellites with eight science instruments. The main goal of MMX and IDEFIX is to determine whether Phobos and Deimos formed from a collision with Mars that created a system of moons, as the latest theories suggest.

References:

• https://presse.cnes.fr/fr/le-cnes-la-jaxa-et-le-dlr-signent-un-accord-tripartite-pour-la-mission-mmx