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A rover for the JAXA MMX Mission to Phobos


Abstract and Figures

The Martian Moons eXploration (MMX) is a mission by the Japan Aerospace Exploration Agency, JAXA, to the Martian moons Phobos and Deimos. It will primarily investigate the origin of this moon by bringing samples back from Phobos to Earth and deliver a small (about 25 kg) Rover to the surface. The Rover is a contribution by the Centre National d’Etudes Spatiales (CNES) and the German Aerospace Center (DLR). Its currently considered scientific payload consists of a thermal mapper (miniRAD), a Raman spectrometer (RAX) a stereo pair of cameras looking forward (NavCAM) and two cameras looking at the interface wheel-surface (WheelCAM) and consequent Phobos’ regolith mechanical properties. The cameras will serve for both, technological and scientific needs. The MMX rover will be delivered from an altitude of <100 m and start uprighting and deploying wheels and a solar generator after having come to rest on the surface. It is planned to operate for three months on Phobos and provide unprecedented science while moving for a few meters to hundreds of meters. MMX will be launched in September 2024 and inserted into Mars orbit in 2025, the Rover delivery and operations are planned for 2026-2027
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IAC-19-A3.4.8 Page 1 of 8
Stephan Ulamec1*, Patrick Michel2, Matthias Grott3, Ute Böttger3, Heinz-Wilhelm Hübers3, Naomi Murdoch4
Pierre Vernazza5, Özgür Karatekin6, Jörg Knollenberg3, Konrad Willner3, Markus Grebenstein7, Stephane Mary8,
Pascale Chazalnoël8, Jens Biele1, Christian Krause1, Tra-Mi Ho9, Caroline Lange9, Jan Thimo Grundmann9, Kaname
Sasaki9, Michael Maibaum1, Oliver Küchemann1, Josef Reill7, Maxime Chalon7, Stefan Barthelmes7, Roy
Lichtenheldt7, Rainer Krenn7, Michal Smisek7, Jean Bertrand8, Aurélie Moussi8, Cedric Delmas8, Simon Tardivel8,
Denis Arrat8, Frans IJpelaan8, Laurence Mélac8, Laurence Lorda8, Emile Remetean8, Michael Lange10, Olaf
Mierheim10, Siebo Reershemius9, Tomohiro Usui11, Moe Matsuoka11, Tomoki Nakamura12, Koji Wada13, Hirdy
Miyamoto14, Kiyoshi Kuramoto15, Julia LeMaitre8, Guillaume Mas8, Michel Delpech8, Loisel Celine8, Arthur
Rafflegeau8, Honorine Boirard8, Roseline Schmisser8, Cédric Virmontois8, Celine Cenac-Morthe8, Dominique
Besson8, Fernando Rull16
1 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), 51147 Cologne, Germany
2 Université Côte d’Azur, Observatoire de la Côte d'Azur, CNRS, Laboratroire Lagrange, 06304 Nice, France
3 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), 12489 Berlin, Germany
4 Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SPAERO), 31055 Toulouse, France
5 Laboratoire d’Astrophysique de Marseille (LAM), 13388 Marseille, France
6 Royal Observatory of Belgium (ROB), Bruxelles, Belgium
7 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), 82234 Oberpfaffenhofen, Germany
8 Centre National d’Etudes Spatiales (CNES), 31401 Toulouse, France
9 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), 28359 Bremen, Germany
10 Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), 38108 Braunschweig, Germany
11 Japan Aerospace Exploration Agency (JAXA), ISAS, 252-5210 Sagamihara, Japan
12 Tohoku University, 980-8578 Sendai, Japan,
13 Chiba Institute of Technology, 275-0016Narashino, Japan
14 University of Tokyo, 113-0033 Tokyo Japan
15 Hokkaido University, Sapporo 060-0810, Japan
16 Universidad de Valladolid Centro de Astrobiología, 47151 Valladolid, Spain
* Corresponding author: Stephan Ulamec, DLR,
The Martian Moons eXploration (MMX) is a mission by the Japan Aerospace Exploration Agency, JAXA,
to the Martian moons Phobos and Deimos. It will primarily investigate the origin of this moon by bringing samples
back from Phobos to Earth and deliver a small (about 25 kg) Rover to the surface.
The Rover is a contribution by the Centre National d’Etudes Spatiales (CNES) and the German
Aerospace Center (DLR). Its currently considered scientific payload consists of a thermal mapper (miniRAD), a
Raman spectrometer (RAX) a stereo pair of cameras looking forward (NavCAM) and two cameras looking at the
interface wheel-surface (WheelCAM) and consequent Phobos’ regolith mechanical properties. The cameras will
serve for both, technological and scientific needs.
The MMX rover will be delivered from an altitude of <100 m and start uprighting and deploying
wheels and a solar generator after having come to rest on the surface. It is planned to operate for three
months on Phobos and provide unprecedented science while moving for a few meters to hundreds of meters.
MMX will be launched in September 2024 and inserted into Mars orbit in 2025, the Rover delivery
and operations are planned for 2026-2027.
The MMX Rover is a contribution by the Centre
National d’Etudes Spatiales (CNES) and the German
Aerospace Center (DLR) to the Mars Moon Explorer
(MMX), a mission by the Japan Aerospace Exploration
Agency, JAXA, to the Martian Moons Phobos and
Deimos [1,2]. It will be delivered to the surface of
Phobos to perform in-situ science but also to serve as a
scout, preparing the landing of the main spacecraft. The
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IAC-19-A3.4.8 Page 2 of 8
MMX Rover will deliver information on the regolith
(geometrical and mechanical) properties by high
resolution imaging of the interface of the wheels with
the surface. Even movies are foreseen.
Phobos exploration with spacecraft goes back to the
1970s, when Mariner 9 took the first images of the
Martian moons. Since then several spacecraft have
taken images (or spectral data) of Phobos, from orbit or
from the Martian surface, respectively [3]. The Origin
of both Phobos and Deimos, however, are still not clear
[4]. Two possible scenarios are currently discussed
among the science community: asteroid capture [5] or
formation after a major impact on Mars [6-8]. The
MMX Mission targets to solve this puzzle by measuring
in great details the properties of Phobos through
measurements from orbit and on the surface and by
returning samples to Earth.
Despite three attempts (Phobos 1 and 2 in 1988 and
Phobos-Grunt in 2011, all were lost before arrival at
Phobos) and several mission studies [e.g. 9-13], there
has been no dedicated mission to the Martian moons,
The Scientific Objectives of the MMX Rover are
defined in line with those of the overall MMX Mission,
however, complementing the science which can be
performed with the instruments onboard the main
spacecraft or the samples returned.
The data provided by the rover thanks to its
instrument suit (see below) are of high interest for the
communities interested in the regolith dynamics in the
low gravity environment of Phobos, in surface processes
and in the geological history of Phobos, in the
composition of Phobos and in its thermal properties.
This data set obtained in-situ is of high value for the
interpretation of data obtained remotely by the
spacecraft by adding ground truth, and to provide a
geological context to the samples that will be returned
to Earth in order to clarify the origin and history of
The Rover will perform:
Regolith science (e.g. dynamics,
mechanical properties like surface strength,
cohesion, adhesion; geometrical properties
like grain size distribution, porosity)
Close-up and high resolution imaging of
the surface terrain
Measurements of the mineralogical
composition of the surface material (by
Raman spectroscopy)
Determination of the thermal properties of
the surface material (surface temperature,
thermal capacity, thermal conductivity)
This will allow determination of the heterogeneity of
the surface material and thus will also help defining the
landing and sampling strategy.
Characterization of the regolith properties shall
considerably reduce the risk of the landing (and
sampling) of the main spacecraft, as the touch-down
strategy can be adapted accordingly.
The Rover design allows the accommodation of four PI
(Principal Investigator) instruments, which are:
Raman Spectrometer RAX and
During phase A also a gravimeter (GRASSE), provided
by the Royal Observatory of Belgium as well as a
lightweight ground penetrating radar (GRAMM) to be
provided by the Technical University Dresden together
with the University Tokyo have been studied. However,
the current limitations regarding mass and volume led to
a removal of those instruments from the baseline
The NavCAMs will be used for autonomous
navigation but also to image the landscape and place
some constraints on the level of heterogeneity of the
regolith both in terms of composition and space
weathering alteration with a higher spatial resolution
with respect to the orbiter. Figure 1 shows a schematic
view of the stereo pair of cameras, Figures 2 and 4 the
position aboard the rover.
They will thereby provide context information for
the remaining rover instruments.
Fig. 1: Schematic view of NavCAM.
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Figure 2: Rover in fully deployed configurations with
positions of MiniRad, rear WheelCAM and NavCAM
stereo bench
There will be two identical WheelCams on the rover
(Figures 3 and 4). These panchromatic cameras have a
2048 x 2048 pixel resolution and a spatial resolution of
approximately 35µm at the center of the image. The
WheelCAMs will be used to image the wheels and their
interaction with the regolith. By observing the
properties of the regolith compaction and flow around
the wheels it will be possible to characterise the
mechanical properties of the regolith itself. In addition,
the WheelCAMs spatial resolution will be sufficient to
characterise the size distribution of regolith particles
and their angularity. Such information is not only
important for understanding the surface properties of
Phobos and how regolith behaves in a low gravity
environment, but this knowledge about the surface will
also lower the risk of the MMX mission.
The CMOS camera sensor for the WheelCAMs, as
well as the NavCAMs has been developed by 3DPLUS
under CNES contract [14].
Figure 3: Image sensor of a WheelCAM (CASPEX
module) [14].
Figure 4: Camera emplacement. Schematic showing the
respective locations and viewing angles of the
NavCAMs and WheelCAMs.
RAX (Raman spectrometer for MMX) is a compact,
low-mass Raman instrument with a volume of
approximately 81х98х125 mm³ and a mass of less than
1.4 kg developed by DLR, INTA/UVA and
JAXA/UTOPS/Rikkyo. It will perform Raman
spectroscopic measurements to identify the mineralogy
of the Phobos surface. The RAX data will support the
characterization of a potential landing site for the MMX
spacecraft and the selection of samples for their return
to Earth. The RAX measurements will be compared
with Raman measurements obtained from the RLS
instrument during the ExoMars 2020 mission, to
provide evidence for the Martian or non-Martian origin
of the surface minerals of Phobos. Furthermore, RAX
measurements will be compared with Raman
measurements performed in Earth laboratories on the
returned samples for better interpretation of the data
acquired. Figure 5 shows a schematic of the
spectrometer module.
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Figure 5: RAX spectrometer module (RSM)
The miniRAD instrument will investigate the
surface temperature and surface thermo-physical
properties of Phobos by measuring the radiative flux
emitted in the thermal infrared wavelength range.
miniRad will use thermopile sensors to measure flux in
6 wavelength bands and obtain information on regolith
[15,16] and boulder [17] thermo-physical properties.
The instrument will thus directly address or contribute
to addressing fundamental MMX science objectives and
provide a basic picture of surface processes on airless
small body. Furthermore, miniRAD will help to
characterize the space environment and the surface
features of Phobos, thus enabling a comparison with
asteroids. The instrument has strong heritage from the
MASCOT radiometer MARA [18].
Figure 6: Conceptual design of the miniRAD sensor
head showing the fields of view of the six individual
infrared channels. The instrument’s field of view will
overlap that of the rover’s navigation stereo cameras.
The overall Rover system consists of 2 ground segments
(one in Germany and one in France) and the flight
hardware. The communication between the Rover
ground segment and the flight segment is linked via the
JAXA MMX mission (JAXA ground segment, ground
stations and MMX main spacecraft).
The MMX Rover flight system consists of the
Mechanical Support System (MECSS) which provides
interface (mechanical fixation, electrical link…)
between the Rover and the main spacecraft and allows
the release and the ejection of the Rover. The RF
communication hardware (antenna and RF electronic
box) aboard the spacecraft is also part of the Rover
flight hardware.
The Rover itself has an internal module referred to
as Service Module (SEM), thermally insulated from the
outside and supporting the electronics, batteries, attitude
sensor and instruments. The service module is
embedded into the chassis (outside walls) which support
the locomotion system and solar generator.
The overall mass of the Rover Flight System (incl.
the units on the main S/C) is 29.1 kg. (see Table 1 for a
mass breakdown). The payload, including the cameras
has an overall mass of about 2.6 kg. Figure 7 shows the
Rover, attached to the MECSS, wheels and solar
generator folded, as in launch/cruise configuration.
Figure 8 shows the rover assembly.
Mass [kg]
Electronics (incl. OBC, battery …)
Attitude sensor
Service module, SEM (structure,
Cameras (all cameras, bench…)
Chassis (structure, shutters, harness…)
Mobility (motors, legs, wheels)
Solar array
RF hardware on main spacecraft
Table 1: Mass breakdown of MMX Rover
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Figure 7: MMX Rover in launch configuration
Figure 8: Exploded view of Rover assembly, showing
Service Module, chassis, locomotion system and solar
IV.I Structure
The two rover system primary structures, Chassis
and MECSS, feature a carbon fibre-reinforced plastic
(CFRP) sandwich designs.
The MECSS is a single sandwich plate design with a
30 mm aluminium honeycomb core and 1.5 mm CFRP
face sheets. Next to providing an interface to the MMX
S/C, the four corners are part of an integrated rover
bearing concept (see Fig. 9). This combines the
interface to the MMX main spacecraft and the rover
bearing as well as the Hold-Down and Release
Mechanism (HDRM) in one integral insert. Thus, the
rover is clamped right at its four bearings, which are
aligned concentrically to the four HDRM frangibolts.
Further the MECSS features a Push-Off Mechanism that
is based on the MASCOT design [19]. After releasing
the HDRM, the Push-Off mechanism will stabilize the
rover and provide it with the required separation energy.
Similarly to the MECSS, the Rover Chassis has two
structural main interfaces, one towards the MECSS and
the other towards the Service Module. During launch
the chassis must remain secured on the MECSS and also
support the Service Module. Once separated from the
MECSS and the MMX spacecraft, respectively, the
Rover chassis must sustain the landing impact on
Phobos surface keeping its structural integrity. Thus, the
chassis features an integral base element and separable
panels closing the base element. Additionally, there are
titanium flanges next to each locomotion unit, which are
part of the base element and redirect loads into the
removable front and rear panel. A top panel, which also
supports the solar generator, is closing the chassis.
Except for the top frame and the locomotion interface
flanges, all parts are sandwich plates (5 mm aluminium
honeycomb core and 0.5 mm CFRP face sheets on each
side). Only the chassis bottom plate, which includes the
main interface with the SEM and the MECSS, as well as
three shutters and the umbilical, is a sandwich plate
including a 10 mm aluminium honeycomb core and
1 mm face sheets.
Figure 9: Top view of the MECSS with central Push-
Off Mechanism. In the four corners a combined
interface to the MMX S/C and the Rover Chassis,
respectively, including the HDRM.
Rover I/F
incl. HDRM
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IV.II Thermal Concept
The thermal control of the MMX Rover is quite
challenging due to the cold environment of Phobos and
the low level of electrical power available for rover
operations and control. In addition, some internal
equipment temperature requirements are difficult to
Power dissipated by the units inside the service
module has to be kept inside as much as possible to
reduce the need of additional heating power.
Consequently, all the thermal leaks between the internal
module, the chassis and the environment have to be
During cruise, the Rover will be heated by the
orbiter via an umbilical to power cruise heaters and read
out thermal sensors for regulation.
On the surface of Phobos the operational modes
have to be chosen carefully to keep the instruments and
electronics within the thermal limits and minimize the
required heating power.
Thermal and power requirements limit the latitudes
on Phobos, where the Rover can be operated.
IV.III Power System
The MMX Rover power architecture is composed
of 3 deployable solar panels and one fixed on the top
panel of the rover, one rechargeable battery and one
power conversion and distribution unit (PCDU). A
particularity for this rover is a connection with MMX
spacecraft umbilical via MECSS equipment. This will
enable the rover to be powered by the spacecraft during
cruise phase. The umbilical and its separation connector
pair are based on technologies already used on PHILAE
and developed further for MASCOT [19].
Power management on board during the operation
phase on Phobos is critical because the solar flux is
limited. To guarantee a positive power budget, the
Rover shall point the solar panels toward the Sun, using
the locomotion subsystem while stationary.
IV.IV Locomotion Concept
The technology for locomotion on the surface of Phobos
is one of the major endeavors of the MMX rover. As the
rover is very compact and light weight, the locomotion
concept is based on four wheels only. No additional
steering actuators are used. The rover features four legs
to bring itself into nominal orientation from any initial
position after landing phase. The sequence of
positioning the four legs to the ground depends on the
achievement of nominal orientation and needs to be
selected autonomously. To increase flexibility on that,
the upper joint is able to perform one full rotation.
Figure 10 shows the main module of the locomotion
system, one leg of the rover.
The wheels have been designed in order to
maximize the likelihood of success even in case of very
soft soil thanks to advanced particle simulations.
The drive train is designed to fulfill three purposes:
execute the self-righting moves required to
bring the rover in an upward position after
drive the rover to a location on the surface
of Phobos,
orient the body of the rover in order to
maximize the performance of the science
instruments and to maximize the energy
flux on the panels.
The actuators and sensors for the four wheels and
legs are all placed inside the rover, to provide a more
advantageous thermal configuration at the cost of a
more complex mechanical design. The actuators are
three phase brushless motor, with a nominal six-step
commutation mode and a stepper mode commutation in
case of sensor error. The leg position is measured
redundantly with two potentiometer technology, a
classical resistive track with grabber and a foil
potentiometer. Finally, a very sensitive joint torque
sensor is used as a safety mechanism to detect
extraordinary torques applied to the legs, most likely
indicating a large rock or an unexpected wheel sinkage.
The motion controller electronics is divided into
three PCBs. Two of them include the power inverter
electronics for providing the motor phase voltages. One
PCB is going to measure the sensor signals, ensure
communications link to OBC via SpaceWire and
compute the control algorithms for all eight actuators.
The MMX Rover is equipped with all the software
and hardware needed to perform autonomous navigation
to overcome the limitations of receiving telemetry and
sending commands between Phobos and Earth, leading
to a drastic reduction of effective speed by manual
operations. The rover can create digital elevation maps,
traversability maps and detect obstacles. Therefore,
once it is confirmed that the rover can drive on the
surface, combined with its path planning and scheduling
software, the rover will be able to safely navigate on the
surface of Phobos, covering much greater distances and
collecting more scientific data. One of the important
activities on ground will be the modeling of the ground
properties based on the collected data in order to drive
faster and more efficiently. Autonomous driving is a
prerequisite in the design of roving vehicles to explore
celestial bodies even more distant than Mars.
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Figure 10: Locomotion system. The image shows one
leg including the wheel and the actuators
IV.V Communication
The RF system for the Rover main spacecraft
communication link will be managed on Rover and
spacecraft side by the rover system.
On board the main spacecraft an S-Band
communication system with a patch antenna will
communicate with the Rover (see Fig. 11).
Figure 11: RF communication on the spacecraft : RF S-
Band and patch antenna
This communications subsystem allows
communication up to 100 km, which covers all mission
phase of the Rover while the MMX spacecraft is in
visibility of the Rover.
The data rate for the telecommand is 32 kbit/s
whereas the data rate for the telemetry can go up to 512
The MMX Rover will be commanded via the MMX
main spacecraft, operated at JAXA. All TMTC will be
linked via the main spacecraft as relay. During cruise,
the rover is connected to MMX via an umbilical, after
separation an S-band RF system will be used.
The Rover itself will be operated from two control
centers, at CNES Toulouse and at DLR/MUSC in
Cologne, respectively.
Operations will be divided into several mission phases:
Launch and Cruise (incl. commissioning, health
Separation-Landing-Upright-Deployment (SLUD)
phase (from separation from the main spacecraft, to
descent, bouncing-phase to the quasi-autonomous
up-righting and solar generator deployment)
Phobos commissioning phase, to check the
functionality of the Rover, its subsystems and
Phobos Operational (Driving & Science) Phase
with a life-time of >100 days (including previous
commissioning phase) on the surface of Phobos.
During this phase different locomotion modes
(including automated) will be tested and
instruments will perform measurements at different
locations on Phobos´ surface.
End of Mission phase (finally passivating the
Figure 12 shows the Rover with its solar generator
deployed as it would be in the Phobos operational phase
on the surface of Phobos.
Figure 12: MMX Rover with deployed wheels and solar
panels in on-surface configuration
The Rover is currently in its phase B and will go
through development and qualification in the coming
years. The logic of development of the Rover is based
on a protoflight approach. The Rover AIT shall start in
2022 and the Flight Model will be delivered to JAXA in
early 2023. The MMX mission is to be launched in
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IAC-19-A3.4.8 Page 8 of 8
Rover operations are currently foreseen for at least
100 days, in 2026. It is currently planned, that MMX
will leave Mars orbit to return to Earth in 2028 [2].
MMX is a JAXA mission with contributions
from NASA, CNES and DLR. The Rover will be
provided by CNES and DLR with science
contributions from Japan and Spain.
The authors would like to thank the teams of MMX
and the Rover as well as the programmatic support to
start this project.
DLR Bremen acknowledges the contribution of
nano-spacecraft developments locally shared with
acknowledges funding support from CNES.
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onboard the Hayabusa2 mission. Space Sci. Rev.,
Vol. 208, pp. 339-374, 2017
... decreasing g) should also be explored (e.g. Saturn's moon Enceladus, which has a gravity level of about 1/100-g, or Mars' moon Phobos, which has a gravity level of about 1/2000-g, for which an upcoming rover mission is planned (Ulamec et al. 2019)). At the wheel speeds and wheel radii studied in our work, for Fr = 1 , g would be 0.001 m/s 2 or 1/10000-g. ...
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Traversing granular regolith, especially in reduced gravity environments, remains a potential challenge for wheeled rovers. Mitigating hazards for planetary exploration rovers requires testing in representative environments, but direct Earth-based testing fails to account for the effect of reduced gravity on the soil itself. Granular scaling laws (GSL) have been proposed in the literature to predict performance of a larger wheel based on tests with a smaller wheel, or to predict performance in one gravity level based on tests in another gravity level. However, this is the first work to experimentally validate GSL in reduced gravity. Here, an expanded version of existing GSL was evaluated experimentally by measuring performance of a single wheel driving through cohesionless lunar soil simulant GRC-1 aboard parabolic flights that reproduce the effects of lunar gravity, and comparing those results to scaled tests performed on the ground. This scaled-wheel testing achieved less than 10% prediction error on three measured output metrics: drawbar pull (i.e. net traction), sinkage, and power draw. Predictions also erred on the conservative side. Subsurface soil imaging revealed similar soil behavior between scaled tests. GSL thus offers an accurate and conservative method for predicting wheel performance in reduced gravity based on 1-g experiments, at least in cohesionless soil.
... more preferred over Charge Coupled Devices (CCD) in many current space imaging missions, such as for the rover MARS 2020 Perseverance [4,5], One Web constellation [6], and selected on MMX [7]. ...
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For the last two decades, the CNES optoelectronics detection department and partners have evaluated space environment effects on a large panel of CMOS image sensors (CIS) from a wide range of commercial foundries and device providers. Many environmental tests have been realized in order to provide insights into detection chain degradation in modern CIS for space applications. CIS technology has drastically improved in the last decade, reaching very high performances in terms of quantum efficiency (QE) and spectral selectivity. These improvements are obtained thanks to the introduction of various components in the pixel optical stack, such as microlenses, color filters, and polarizing filters. However, since these parts have been developed only for commercial applications suitable for on-ground environment, it is crucial to evaluate if these technologies can handle space environments for future space imaging missions. There are few results on that robustness in the literature. The objective of this article is to give an overview of CNES and partner experiments from numerous works, showing that the performance gain from the optical stack is greater than the degradation induced by the space environment. Consequently, optical stacks can be used for space missions because they are not the main contributor to the degradation in the detection chain.
... This will return high-resolution information on the shape file, but obviously only on the side/region of impact. The same is true for the Juventas CubeSat landing on Dimorphos (Goldberg et al., 2019), and the MMX mission with a planned rover deployment (Ulamec et al., 2019) and a surface-sample-acquisition-manoeuvre (Kuramoto et al., 2022). All these examples have in common that they will return detailed surface information on the surface surrounding the landing point/rover operation region. ...
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In classical gravimetry, different corrections are applied, e.g. to correct for the measurement elevation above a reference plane and the gravitational attraction of the material lying between the measurement point and reference plane. Additionally, and especially in non-flat regions, a correction for the topography is generally needed. While this contribution is relatively small on spherical celestial objects, it can be more important for irregularly shaped bodies, such as small bodies or some natural satellites. With the surface gravity being much smaller, the relative importance of the topographic correction increases, while the approximation errors of the surface will become larger. In this work, the novel Wedge-Pentahedra Method (WPM) for topographic correction for (near-) surface gravimetric measurements and simulations is presented that allows precise topographic corrections for asteroids and natural satellites. For a first study, the WPM is applied to the Martian moon Phobos. Taking an exemplary surface location, a high-resolution artificial terrain is added to the surrounding, and the gravitational influence of this topography compared to the original surface is assessed. It is found that the influence of topography on the surface gravity of a small body such as Phobos can be in the order of a few percent, making it an important correction not only for surface gravity science, but likewise for landing and surface operations, to best ensure the mission success. Therefore, the here presented WPM opens a manifold of possible future applications in the context of Solar System exploration, regarding both space science and space technology.
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Phobos, a satellite of Mars, was successfully studied by flyby, orbiter, and landing missions to the Red Planet, but several questions remain about its origin, composition, and relationship to Mars. It is suggested that Phobos is either a captured body from the asteroid belt or the outer Solar System (capture scenario), or a consequence of re-accreted ejecta from Mars ( in situ formation/giant impact). So far, Phobos has been characterized by its two spectral units - blue and red - with different compositional restrains. The red unit represents most of the surface, while the blue unit is focused on the Stickney crater and surroundings. In the absence of samples returned from this satellite, simulant regolith must be studied to infer various proprieties, and complement in situ studies. To date, there are three simulants of this satellite: Phobos-1C, Phobos Captured Asteroid-1 (PCA-1), and Phobos Giant Impact-1 (PGI-1). Since Phobos may have a Mars-like composition, terrestrial analogues of Mars should also be analysed. The data retrieved from the various assays performed with these planetary field analogues may be used as a database to complement future space missions to Phobos, but, ultimately, the composition of Phobos will have to be analysed by a sample-return mission.
Conference Paper
In any mechatronic system, faults can occur. Likewise also in the MMX rover, which is a wheeled rover mutually developed by CNES (Centre national d’ ́etudes spatiales) and DLR (German Aerospace Center), intended to land on Phobos. An essential part of the MMX rover is the locomotion subsystem which includes several sensors and eight motors actuating the four legs and the four wheels. In each of these components and their interfaces, there is a possibility that faults arise and lead to subsystem failures, which would mean that the rover cannot move anymore. To reduce this risk, the possible faults of the MMX locomotion subsystem were identified in a FMECA study and their criticality was classified, which is presented in here. During this examination, the criticality was graded depending on different mission phases. With the help of this study, the hardware, firmware and software design were enhanced. Fur- ther, certain fault detection, isolation and recovery strategies were implemented in the locomotion firmware and software as well as in the full rover software.
Conference Paper
The MMX Rover, developed by CNES and DLR, will fly to and explore the surface of the Martian Moon Phobos within the JAXA Martian Moon Exploration Mission. It will be the first wheeled locomotion system in a milli-g environment. In the development of the rover, simulations have been used to test and develop its robotic activities. This paper presents the multi-physics simulations that are being used. The overall simulator setup and its main components are discussed. To provide appropriate simulations for the var-ious topics while maintaining a unified simulator, a modular approach was required. The different modules and their role will be outlined. For this, Dymola's implementation of the Mod-elica modeling language provides the basis, especially regarding multi-body dynamics, and the possibility to include external libraries, e. g. for environment interaction, control logic and visualization. Finally, examples for the simulator used in driving, uprighting, alignment and separation will be presented. These examples illustrate the approach on experiment design, setup and result evaluation. To date the MMX Rover simulator is regarded as an indispensable development and analysis tools, especially since representative lab experiments are much limited when designing a robotic system for milli-g operations. It is also planned to be used during operations phase for planning and analysis.
Conference Paper
This paper motivates and details the tools used to control a planetary exploration rover prototype and its simulation twin. The novelty is the coupling of the prototype and the simulation. The prototype and simulation of the rover use the same software tools and code for communication, signal processing, data storage and drive control algorithms. The presented toolchain is unprecedented for mobile robot to the best of the authors' knowledge, yet generic and versatile enough that it can easily be adapted to different kinds of robotic systems as the full paper will show. Advantages and drawbacks as well as comparison to other solutions are also key content of this text. DLR's Institute of System Dynamics and Control (SR) is developing a new mobile robot called \textquotedblScout\textquotedbl that will serve as the example of the toolchain. The Scout rover is a robust cave exploration rover, based on rimless wheels and biologically inspired locomotion mechanisms. It consists of segments interconnected by elastic \textquotedblvertebrae\textquotedbl in longitudinal direction. Some of the special features of this rover design can only reasonably be unfold thanks to the toolchain, e.g. the bionic phase shift control or simulative exploration of different rover and wheel configurations. The development of the Scout rover relies on modeling, simulation and optimization and follows the \textquotedblV\textquotedbl-shaped paradigm of system development. Elements of rapid control prototyping are implemented and commercial of the shelf sensors, actuators and computation units integrated. This has rapidly led to a robust mobile robot that is capable to cross obstacles that are larger than the radius of the wheels. The Scout rover development relies on the Modelica language for guiding and safeguarding virtual design decisions as well as for rapid control prototyping using the commercial Modelica modeling and simulation environment Dymola. Using this toolchain is a good compromise for satisfying the requirements in terms of rapid control prototyping. It has effective facilities for modeling the challenging physics for reliable Model-in-the-Loop simulations, at the same time the model of the controller can be directly used on the prototype's hardware. A well-thought-out model structure allows a transparent and seamless swapping between virtual model components and model components which drive physical drives and sensors. The actuators of the prototype are addressed using the EtherCAT protocol, communication with sensors and human operators goes through a light-weight in-house middleware and logged data is stored in the popular HDF5 format. Coordination of the actuators and reaction to user input in a state machine like manner is implemented with scripts in the Lua language. Steps for further work include integration of cameras and implementation of obstacle detection, additional control algorithms and more autonomy. Operations in the field of a space mission is envisioned around 2030. The presented toolchain is thought-out enough that this won't require major changes even when COTS parts need to be replaced by space qualified hardware. Likewise, the simulation of the rover will remain an important activity.
Conference Paper
Martian Moons eXploration (MMX) is a joint project of the French, German and Japanese space agencies Centre national d'etudes spatiales (CNES), German Aerospace Center (DLR) and Japan Aerospace Exploration Agency (JAXA) for an exploration mission to the moons of Mars, i.e. Phobos and Deimos. CNES and DLR are providing a rover payload to the mother spacecraft of JAXA which is designated to be the first rover to drive in milli-g-environment. Locomotion in milli-g-environment on potentially hazardous terrain with steep slopes and high sinkage raises increased demands on the locomotion subsystem and control algorithms. The MMX-Rover chassis control algorithms (CCA) are embedded as part of the MMX-Rover locomotion software partition in a three layer architecture between the Command and Control Software and the hardware-related Basic Software. This paper proposes a trajectory-based generic chassis control framework as extended chassis control variant for the MMX-Rover. The rover locomotion possibilities are formulated upon a generic rover motion interface to derive analytical solutions for the specialized MMX-Rover locomotion modes. The resulting algebraic chassis control algorithms (A-CCA) are mathematically formulated in detail. A connection to meta-modelling for kinematic locomotion functions is established. The generic chassis control framework can be used to formulate the onboard control algorithms as minimal application code or generic application code. The decision between the minimal or generic code formulation variant practically influences the control software architecture and implementation. The generic chassis control framework is used as a practical analysis and verification tool to ensure the qualification of a geometrically inspired and kinematically simplified control algorithm variant (G-CCA) as flight software candidate. In particular, the algebraic equations originating from the generic chassis control framework are compared to the geometric control algorithms regarding their functional scope, kinematic formulation and practical software implementation. Results for the analysis and verification of G-CCA are shown and their qualification in terms of the locomotion functional coverage and rover motion behavior discussed. The generic chassis control framework contributes to ensure and enhance the functioning and quality of the control algorithms in the MMX-Rover mission context.
Conference Paper
Wheeled rovers have been successfully used as mobile landers on Mars and Moon and more such missions are in the planning. For the Martian Moon eXploration (MMX) mission of the Japan Aerospace Exploration Agency (JAXA), such a wheeled rover will be used on the Marsian Moon Phobos. This is the first rover that will be used under such low gravity, called milli-g, which imposes many challenges to the design of the locomotion subsystem (LSS). The LSS is used for unfolding, standing up, driving, aligning and lowering the rover on Phobos. It is a entirely new developed highly-integrated mechatronic system that is specifically designed for Phobos. Since the Phase A concept of the LSS, which was presented two years ago [1], a lot of testing, optimization and design improvements have been done. Following the tight mission schedule, the LSS qualification and flight models (QM and FM) assembly has started in Summer 2021. In this work, the final FM design is presented together with selected test and optimization results that led to the final state. More specifically, advances in the mechanics, electronics, thermal, sensor, firmware and software design are presented. The LSS QM and FM will undergo a comprehensive qualification and acceptance testing campaign, respectively, in the first half of 2022 before the FM will be integrated into the rover
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C-type asteroids are among the most pristine objects in the Solar System, but little is known about their interior structure and surface properties. Telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. This includes observations of C-type asteroid (162173) Ryugu1–3. However, on arrival of the Hayabusa2 spacecraft at Ryugu, a regolith cover of sand- to pebble-sized particles was found to be absent4,5 (R.J. et al., manuscript in preparation). Rather, the surface is largely covered by cobbles and boulders, seemingly incompatible with the remote-sensing infrared observations. Here we report on in situ thermal infrared observations of a boulder on the C-type asteroid Ryugu. We found that the boulder’s thermal inertia was much lower than anticipated based on laboratory measurements of meteorites, and that a surface covered by such low-conductivity boulders would be consistent with remote-sensing observations. Our results furthermore indicate high boulder porosities as well as a low tensile strength in the few hundred kilopascal range. The predicted low tensile strength confirms the suspected observational bias⁶ in our meteorite collections, as such asteroidal material would be too frail to survive atmospheric entry⁷.
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The MASCOT radiometer MARA on board the Hayabusa2 mission will measure surface brightness temperatures on the surface of asteroid (162173) Ryugu in six wavelength bands. Here we present a method to constrain surface thermophysical properties from MARA measurements. Moreover, uncertainties when determining surface thermal inertia as well as emissivity are estimated. Using data from all filters and assuming constant emissivity, thermal inertia of a homogeneous surface can be determined with an uncertainty range of 250 ±16 Jm⁻²K⁻¹s−1/2, while the emissivity uncertainty is below 6%. Similar results are obtained if emissivity is allowed to vary as a function of wavelength and if the MARA channels with the best signal-to-noise ratio are used to constrain thermal inertia. If the observed surface is heterogeneous and two morphologically different units are present in the instrument's field of view, thermal inertia of the subunits can be retrieved independently if their contrast in terms of thermophysical properties is large enough. If, for example, the surface is covered by equal area fractions of fine-grained and coarse-grained material, then thermal inertia is found to be retrievable with uncertainties of 658 ±78 and 54 ±22 Jm⁻²K⁻¹s−1/2 for the coarse-grained and fine-grained fraction, respectively.
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On December 3rd, 2014, the Japanese Space Agency (JAXA) launched successfully the Hayabusa2 (HY2) spacecraft to its journey to Near Earth asteroid (162173) Ryugu. Aboard this spacecraft is a compact landing package, MASCOT (Mobile Asteroid surface SCOuT), which was developed by the German Aerospace Centre (DLR) in collaboration with the Centre National d’Etudes Spatiales (CNES). Similar to the famous predecessor mission Hayabusa, Hayabusa2, will also study an asteroid and return samples to Earth. This time, however, the target is a C-type asteroid which is considered to be more primitive than (25143) Itokawa and provide insight into an even earlier stage of our Solar System. Upon arrival at asteroid Ryugu in 2018, MASCOT will be released from the HY2 spacecraft and gently descend by free fall from an altitude of about 100 m to the surface of the asteroid. After a few bounces, the lander will come to rest at the surface and perform its scientific investigations of the surface structure and mineralogical composition, the thermal behaviour and the magnetic properties by operating its four scientific instruments. Those include an IR imaging spectrometer (MicrOmega, IAS Paris), a camera (MASCAM, DLR Berlin), a radiometer (MARA, DLR Berlin) and a magnetometer (MASMAG, TU Braunschweig). In order to allow optimized payload operations the thermal design of MASCOT is required to cope with the contrasting requirements of the 4-year cruise in cold environment versus the hot conditions on the surface of the asteroid. Operations up to 2 asteroid days (∼16 hours) based on a primary battery are currently envisaged. A mobility mechanism allows locomotion on the surface. The mechanism is supported by an attitude and motion sensing system and an intelligent autonomy manager, which is implemented in the onboard software that enables MASCOT to operate fully independently when ground intervention is not available.
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Despite many efforts an adequate theory describing the origin of Phobos and Deimos has not been realized. In recent years a number of separate observations suggest the possibility that the martian satellites may have been the result of giant impact. Similar to the Earth-Moon system, Mars has too much angular momentum. A planetesimal with 0.02 Mars masses must have collided with that planet early in its history in order for Mars to spin at its current rate (Dones, L., Tremaine, S. [1993]. Science 259, 350-354). Although subject to considerable error, current crater-scaling laws and an analysis of the largest known impact basins on the martian surface suggest that this planetesimal could have formed either the proposed 10,600 by 8500-km-diameter Borealis basin, the 4970-km-diameter Elysium basin, the 4500-km-diameter Daedalia basin or, alternatively, some other basin that is no longer identifiable. It is also probable that this object impacted Mars at a velocity great enough to vaporize rock (>7 km/s), which is necessary to place large amounts of material into orbit. If material vaporized from the collision with the Mars-spinning planetesimal were placed into orbit, an accretion disk would have resulted. It is possible that as material condensed and dissipated beyond the Roche limit forming small, low-mass satellites due to gravity instabilities within the disk. Once the accretion disk dissipated, tidal forces and libration would have pulled these satellites back down toward the martian surface. In this scenario, Phobos and Deimos would have been among the first two satellites to form, and Deimos the only satellite formed - and preserved - beyond synchronous rotation. The low mass of Phobos and Deimos is explained by the possibility that they are composed of loosely aggregated material from the accretion disk, which also implies that they do not contain any volatile elements. Their orbital eccentricity and inclination, which are the most difficult parameters to explain easily with the various capture scenarios, are the natural result of accretion from a circum-planetary disk.
This paper focuses on the radiation-induced dose and single-event effects (SEEs) on a color CMOS camera designed for space missions. The γ -ray and proton tests are used to evaluate the tolerance against cumulative dose effects. The dark current of the image sensor is the main parameter impacted by dose effects. Heavy ions testing is performed to evaluate SEEs. single-event upset, single-event functional interrupt, and single-event latchup have been observed and mitigation techniques were proposed for specific space missions.
DePhine – Deimos and Phobos Interior Explorer – is a mission proposed in the context of ESA’s Cosmic Vision program, for launch in 2030. The mission will explore the origin and the evolution of the two Martian satellites, by focusing on their interior structures and diversity, by addressing the following open questions: Are Phobos and Deimos true siblings, originating from the same source and sharing the same formation scenario? Are the satellites rubble piles or solid bodies? Do they possess hidden deposits of water ice in their interiors? The DePhine spacecraft will be inserted into Mars transfer and will initially enter a Deimos quasi-satellite orbit to carry out a comprehensive global mapping. The goal is to obtain physical parameters and remote sensing data for Deimos comparable to data expected to be available for Phobos at the time of the DePhine mission for comparative studies. As a highlight of the mission, close flybys will be performed at low velocities, which will increase data integration times, enhance the signal strength and data resolution. 10 – 20 flyby sequences, including polar passes, will result in a dense global grid of observation tracks. The spacecraft orbit will then be changed into a Phobos resonance orbit to carry out multiple close flybys and to perform similar remote sensing as for Deimos. The spacecraft will carry a suite of remote sensing instruments, including a camera system, a radio science experiment, a high-frequency radar, a magnetometer, and a Gamma Ray / Neutron Detector. A steerable antenna will allow simultaneous radio tracking and remote sensing observations (which is technically not possible for Mars Express). Additional instrumentation, e.g. a dust detector and a solar wind sensor, will address further science goals of the mission. If Ariane 6-2 and higher lift performance are available for launch (the baseline mission assumes a launch on a Soyuz Fregat), we expect to have greater spacecraft mobility and possibly added payloads.
The Martian moons Phobos and Deimos may have accreted from a ring of impact debris, but explaining their origin from a single giant impact has proven difficult. One clue may lie in the orbit of Phobos that is slowly decaying as the satellite undergoes tidal interactions with Mars. In about 70 million years, Phobos is predicted to reach the location of tidal breakup and break apart to form a new ring around the planet. Here we use numerical simulations to suggest that the resulting ring will viscously spread to eventually deposit about 80% of debris onto Mars; the remaining 20% of debris will accrete into a new generation of satellites. Furthermore, we propose that this process has occurred repeatedly throughout Martian history. In our simulations, beginning with a large satellite formed after a giant impact with early Mars, we find that between three and seven ring–satellite cycles over the past 4.3 billion years can explain Phobos and Deimos as they are observed today. Such a scenario implies the deposition of significant ring material onto Mars during each cycle. We hypothesize that some anomalous sedimentary deposits observed on Mars may be linked to these periodic episodes of ring deposition.
Conference Paper
PADME is a proposed NASA Discovery mission to investigate the origin of two remarkable and enigmatic small bodies, Phobos and Deimos, the two moons of Mars.
Although the two moons of Mars, Phobos and Deimos, have long been thought to be captured asteroids, recent observations of their compositions and orbits suggest that they may have formed from debris generated by one or more giant impacts of bodies with ∼0.01× target mass. Recent studies have both analytically estimated debris produced by giant impacts on Mars and numerically examined the evolution of circum-Mars debris disks. We perform a numerical study (Smoothed Particle Hydrodynamics simulation) of debris retention from giant impacts onto Mars, particularly in relation to a Borealis-scale giant impact ( J) capable of producing the Borealis basin. We find that a Borealis-scale impact is capable of producing a disk of mass ∼ kg (∼1–4% of the impactor mass), sufficient debris to form at least one of the martian moons according to recent numerical studies of martian debris disk evolution. While a Borealis-scale impact may generate sufficient debris to form both Phobos and Deimos, further studies of the debris disk evolution are necessary. Our results can serve as inputs for future studies of martian debris disk evolution.
Mars' moons Phobos and Deimos are low-albedo, D-type bodies that may preserve samples of outer solar system material that contributed organics and volatiles to the accreting terrestrial planets. A Discovery-class mission concept described in this paper, the Mars-Moon Exploration, Reconnaissance and Landed Investigation (MERLIN), will obtain in situ measurements from Deimos to test models for the moon's origin. The measurement objectives of MERLIN are to determine Deimos' elemental and mineralogical composition, to investigate its volatile and organic content, and to characterize processes that have modified its surface. To achieve these objectives, a landed payload will provide stereo imaging and measurements of elemental and mineralogical composition and interior structure. An orbital payload will acquire global high-resolution and color imaging, putting the landing site in context by characterizing Deimos' geology. Following MOI the spacecraft flies in formation with Deimos, and uses small changes in its orbit around Mars to investigate Deimos from a range of altitudes and illuminations over 4 months. Data taken during 1- to 2-km altitude flyovers will certify a landing site. The spacecraft will be delivered to a point several kilometers above Deimos, and will navigate to landing on a fresh exposure of regolith using onboard imaging. 90 days of baseline landed operations will provide a complete set of measurements, with schedule reserve, and there is sufficient propellant to repeat the measurements at a second site.