30. September 2020
In free fall to the Martian moon Phobos

First tests for land­ing the Mar­tian Moons eX­plo­ration Rover

Preparations for a drop test
Prepa­ra­tions for a drop test
Image 1/7, Credit: © DLR. All rights reserved

Preparations for a drop test

In the cur­rent ex­per­i­ments, the re­searchers are drop­ping the pre­lim­i­nary mod­el of the MMX Rover un­der lab­o­ra­to­ry con­di­tions from a height of five cen­time­tres on­to a change­able sur­face at var­i­ous an­gles to test its ro­bust­ness.
Assembly of the preliminary MMX Rover model
As­sem­bly of the pre­lim­i­nary MMX Rover mod­el
Image 2/7, Credit: © DLR. All rights reserved

Assembly of the preliminary MMX Rover model

The pre­lim­i­nary test mod­el of the MMX Rover al­ready has two wheels (back­ground) and is be­ing used to de­tect and ad­dress po­ten­tial struc­tural weak­ness­es. Mea­sur­ing 47.5 cen­time­tres by 55 cen­time­tres by 27.5 cen­time­tres, the rover hous­ing is a lightweight con­struc­tion com­pris­ing pre­cise­ly stiff­ened sand­wich com­po­nents with out­er lay­ers made of car­bon-fi­bre-re­in­forced poly­mers (CFRP) and cores made of alu­mini­um hon­ey­comb.
Sim­u­la­tion of the MMX Rover land­ing
Video 3/7, Credit: DLR (CC BY-NC-ND 3.0)

Simulation of the MMX Rover landing

Length: 00:01:52
To anal­yse how the MMX Rover will be­have un­der the con­di­tions of re­duced grav­i­ty on Pho­bos, the DLR In­sti­tute of Sys­tem Dy­nam­ics and Con­trol is con­duct­ing com­plex sim­u­la­tions. This sim­u­la­tion shows the par­tic­u­lar­ly chal­leng­ing mis­sion phase of the fi­nal mo­ments of the land­ing and the sub­se­quent re­ori­en­ta­tion of the rover, de­ploy­ment of the so­lar pan­els and align­ment with the Sun. Af­ter this com­plete­ly au­tonomous se­quence, the MMX Rover will be able to charge its bat­tery op­ti­mal­ly for its first jour­ney on Pho­bos. Sim­u­la­tions such as these are used in the project to gen­er­ate im­por­tant find­ings for the fur­ther de­vel­op­ment of the rover.
Drop tests in the DLR Landing and Mobility Test Facility
Drop tests in the DLR Land­ing and Mo­bil­i­ty Test Fa­cil­i­ty
Image 4/7, Credit: © DLR. All rights reserved

Drop tests in the DLR Landing and Mobility Test Facility

Drop tests with the pre­lim­i­nary mod­el of the MMX Rover are tak­ing place in the Land­ing and Mo­bil­i­ty Test Fa­cil­i­ty (Lande- und Mo­bil­ität­stest An­lage; LAMA) at DLR Bre­men.
Model of the MMX Rover undergoing vibration tests
Mod­el of the MMX Rover un­der­go­ing vi­bra­tion tests
Image 5/7, Credit: © DLR. All rights reserved

Model of the MMX Rover undergoing vibration tests

To im­prove the ac­cu­ra­cy of the me­chan­i­cal sim­u­la­tion mod­el, tests on the vi­bra­tion be­haviour of the rover struc­ture are al­so be­ing car­ried out as part of the cam­paign.
Image of Phobos acquired by the nadir channel of HRSC
Im­age of Pho­bos ac­quired by the nadir chan­nel of HRSC
Image 6/7, Credit: ESA/DLR/FU Berlin CC BY-SA 3.0 IGO

Image of Phobos acquired by the nadir channel of HRSC

Im­age of the Mars moon Pho­bos ac­quired by the High Res­o­lu­tion Stereo Cam­era (HRSC) nadir chan­nel at full res­o­lu­tion in the course of a fly­by that took place on 12 Septem­ber 2017 dur­ing or­bit 17,342 of ESA’s Mars Ex­press space­craft.
The MMX Rover moving on Phobos
The MMX Rover mov­ing on Pho­bos
Image 7/7, Credit: DLR (CC BY-NC-ND 3.0)

The MMX Rover moving on Phobos

The land­ing of the MMX Rover on the Mar­tian moon Pho­bos is planned for late 2026 or ear­ly 2027. It will ex­plore the sur­face for ap­prox­i­mate­ly three months.
  • Intensity of the landing impact on Mars’ moon Phobos is being tested with a rover model.
  • The housing of the rover consists of a lightweight construction made of carbon-fibre-reinforced polymers (CFRP).
  • The landing on Phobos is planned for late 2026 or early 2027 as part of the MMX mission.
  • Focus: Space, robotics, exploration, Mars

The Japan Aerospace Exploration Agency (JAXA) Martian Moons eXploration (MMX) mission will have a German-French rover on board when it is launched in 2024. The rover will land on the Martian moon Phobos and explore its surface for approximately three months. Initial landing tests are currently underway at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Landing and Mobility Test Facility (Lande- und Mobilitätstest Anlage; LAMA) in Bremen. Using a first preliminary development model, the engineers are determining how robust the design of the approximately 25-kilogram rover must be to withstand an impact on the moon's surface after a free fall of about 40 to 100 metres.

"Under laboratory conditions, we drop the preliminary model of the MMX Rover from a height of five centimetres onto a changeable surface at various angles," explains Test Manager Michael Lange from the DLR Institute of Composite Structures and Adaptive Systems. "In this way, since Phobos has only approximately two thousandths of Earth's gravity at its surface, we can simulate the intensity of the impact for the rover structure." A particular challenge is that the free-falling rover could arrive at the surface in any orientation, possibly also hitting a rock. "To simulate this situation, we are using two hemispheres with diameters of two and nine centimetres that are positioned in a bed of sand, in addition to a flat plate," says Michael Wrasmann from the DLR Institute of Space Systems. "The exact location of the landing on the surface of Phobos is a matter of chance and we are using these analyses to prepare for the various possible scenarios."

An MMX Rover wheel
An MMX Rover wheel
The preliminary test model of the MMX Rover already has two wheels.

Cores made of aluminium honeycomb

The preliminary test model in the laboratory already resembles the final MMX Rover, with two mounted wheels and two dummy wheels and a mechanical safety system for launch and landing . It is being used to detect and address potential structural weaknesses in as much detail as possible. The rover's 47.5-centimetre by 55-centimetre by 27.5-centimetre housing is a lightweight construction comprising precisely stiffened sandwich components with outer layers made of carbon-fibre-reinforced polymers (CFRP) and cores made of aluminium honeycomb. In addition to the laboratory tests, extensive computer simulations are also being carried out to cover a wide range of other landing situations. In order to improve the accuracy of the mechanical simulation model, tests on the vibration behaviour of the rover structure are also being carried out as part of the campaign. The findings of the experiments will help the researchers to define the design of the MMX Rover in more detail. "In 2021, we plan to test a significantly more representative structural model equipped with all the components of the motion system. This consists of four wheels attached to movable legs and a foldable mechanism at the rear of the rover. If the rover lands on its side, this mechanism will bring it into a position where it can autonomously move into the final driving orientation and deploy its solar panels," explains DLRs overall Project Manager for the MMX Rover, Markus Grebenstein from DLR’s Robotics and Mechatronics Center (RMC) in Oberpfaffenhofen.

In addition to the structural stresses caused by the landing, the rover will be exposed to extreme environmental conditions. Phobos heats up from -150 to +50 degrees Celsius within a day-night cycle that lasts just over seven hours. The interior of the rover must be actively maintained at a comparatively constant temperature to ensure the quality of the scientific measurements. “For this reason, extensive tests of the temperature behaviour of the rover will also be carried out in 2021 using a thermal model,” Grebenstein continues.

The launch of the rover with the JAXA Martian Moons eXploration (MMX) mission is scheduled for 2024, with insertion into Mars orbit in 2025. The mission's targets are the two moons Phobos and Deimos, which might be asteroids captured by the Red Planet or may have formed as a result of the collision of a larger body with Mars. The formation mechanism of the Mars, Phobos and Deimos system is one of the keys to a better understanding of planet formation in the Solar System. The landing of the MMX rover as part of the mission is planned for late 2026 or early 2027. It will spend approximately 100 days analysing the surface properties of the Martian moon in detail and thus contribute to solving the scientific puzzle concerning its origin.

Cooperation in partnership

The German-French MMX Rover is being designed and built under the joint management of DLR and CNES (Centre National d'Études Spatiales). DLR is responsible for the development of the rover structure and the entire locomotion system, which also contributes to the reorientation and enables uprighting, as well as two instruments, a Raman spectrometer and a radiometer, each measuring the composition and properties of the surface. CNES is responsible for the camera systems for spatial orientation and exploration on the surface and for the investigation of mechanical soil properties, as well as development of the central service module including the rover's on-board computer and the power and communication system. After landing, the rover will be operated by control centres at DLR and CNES.

The MMX mission continues the many years of successful collaboration between the partners JAXA, DLR and CNES. It is following in the footsteps its successful predecessor mission, Hayabusa2, in which JAXA sent a spacecraft to the asteroid Ryugu with the German-French Mobile Asteroid Surface Scout (MASCOT) lander on board. On 3 October 2018 MASCOT sent spectacular images back to Earth showing a landscape with large amounts of debris and rocks, but almost no dust – which scientists had expected to find on Ryugu. Hayabusa2 collected samples from Ryugu and is currently bringing them back to Earth. The asteroid samples are contained in a capsule that is scheduled to land in Australia on 6 December 2020 and will then be examined in the laboratory.

  • Falk Dambowsky
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Linder Höhe
    51147 Cologne
  • Dipl.-Ing. Michael Lange
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Com­pos­ite Struc­tures and Adap­tive Sys­tems
    Lilienthalplatz 7
    38108 Braunschweig
  • Markus Grebenstein
    Deputy Di­rec­tor
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Robotics and Mecha­tron­ics
    Münchener Straße 20
    82234 Oberpfaffenhofen-Weßling
  • Michael Wrasmann
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Space Sys­tems
    Sys­tems En­gi­neer­ing and Project Of­fice
    Robert-Hooke-Straße 7
    28359 Bremen

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