MMX Locomotion Subsystem: mechanics for extraterrestrial low gravity drive

The advent of exploring low-gravity environments gives the opportunity to land rovers on celestial bodies without any landing platform and perform manipulative tasks under mostly unknown conditions. In addition to common loads, for example vibration, operation and thermal loads, the rover will face also impact loads during touchdown. This circumstance requires additional mechanisms to protect exposed parts, like the legs and wheels of a rover. Previous research attaches the wheels to the rover body or the landing platform through cup-cone interfaces at the wheel hub, which leads to unfavorable force distribution at the wheel rim in certain load cases, especially if the wheel represents the first point of contact during touchdown. This paper gives a detailed description in the mechanical design and testing of the locomotion subsystem (LSS) of the Martian Moons eXploration (MMX) rover. As the rover will fall to the moon Phobos unprotected and without any landing platform, the exposed locomotion subsystem has a high probability of being the initial contact point at touchdown. Besides the drivetrains and thermal hardware, a novel hold down and release mechanism (HDRM) will be introduced as an integral part of the locomotion subsystem. The HDRM is realized using three support structures at the wheel rim and one fixation in the wheel axis. In this way, the exposed locomotion subsystem will be stabilized in described load cases, since each support structure forms a closed kinematic loop with the wheel and the central fixation in stowed configuration. This approach leads to vibration and impact resistant behavio

Conquering the Cold: Thermal Testing of MMX Rover IDEFIX's Locomotion Subsystem for the Exploration on Phobos

The Martian Moon eXploration (MMX) mission, led by the Japan Aerospace Exploration Agency (JAXA), is scheduled for launch in 2024 with the objective of sample-return from the Martian Moon Phobos and additional scientific observations of Deimos. As part of this mission, the MMX rover 'IDEFIX', developed collaboratively by the French Centre National d'Études Spatiales (CNES) and the German Aerospace Center (DLR), will serve as a mobile scout on the surface of Phobos. With its four-wheeled design and a weight of 25 kg, the rover will operate in microgravity and conducting in-situ measurements in areas of scientific interest. The locomotion subsystem (LSS) of the MMX rover, developed, build and qualified by DLR's Robotics and Mechatronics Center, plays a key role in fulfilling the mission objectives. The LSS is designed to accomplish various high-level requirements, including the correct reorientation (so-called uprighting) of the rover after ballistic landing, precise alignment of the solar cells for optimal power generation, and the provision of different driving modes to explore Phobos and interact with its surface. Additionally, the LSS allows for adjusting the rover's ground distance to allow measurements with the Raman spectrometer. To ensure the LSS can withstand the challenging conditions of the MMX mission, particularly the harsh environment during the cruise phase and the expected extremely low temperatures on Phobos, a comprehensive thermal design was developed. The LSS was subsequently subjected to rigorous testing throughout the development phases. The testing involved evaluating the mechanical, electrical and thermal aspects of various subunits, including the complex hold-down and release mechanism (HDRM), as well as conducting full functionality tests of the flight representative LSS during the qualification and acceptance stages. This presentation provides an overview of DLR's approach to thermal testing activities for the LSS during the development phase of the MMX rover. It offers insights into the MMX mission as a whole and presents a detailed examination of the qualification and acceptance thermal tests conducted for the LSS, emphasizing the significance of these tests in ensuring the successful operation of the rover during the mission

Driving in Milli-G: The Flight Model of the MMX Rover Locomotion Subsystem and its Integration & Testing in the Rover

IDEFIX is a 25 kg four-wheeled rover that will explore the surface of the Martian Moon Phobos in 2027. The rover is jointly developed by the German Aerospace Center (DLR) and the Centre National d'Etudes Spatiales (CNES) and will be brought to Phobos within the Japan Aerospace Exploration Agency's (JAXA) Martian Moon eXploration (MMX) mission. Being the world's first wheeled system to drive in milli-gravity, IDEFIX's locomotion deserves special attention. This paper gives an overview of the locomotion subsystem (LSS) of the rover, which is entirely developed and built by the Robotics and Mechatronics Center of DLR (DLR-RMC). A representative LSS, mounted on an IDEFIX prototype, is shown in Figure 1. The LSS is tailored to the needs for the IDEFIX rover and the most important, sizing challenges and functional requirements are summarized. It is then shown how the final flight model (FM) design answers to these requirements. The assembly, integration and testing (AIT) with respect to the LSS consists of several steps of integration and testing at different facilities as well as a comprehensive test sequence once the rover is mostly integrated. Since the LSS is an important, interconnected and the functionally most complex subsystem of the rover, some functionalities could only be tested once the LSS was integrated into IDEFIX. These AIT aspects are therefore summarized in this paper as well

MMX - development of a rover locomotion system for Phobos

The MMX mission (Martian Moons eXploration) is a robotic sample return mission of the JAXA (Japan Aerospace Exploration Agency), CNES (Centre National d'Etudes Spatiales ) and DLR (German Aerospace Center) for launch in 2024. The mission aims to answer the question on the origin of Phobos and Deimos which will also help to understand the material transport in the earliest period of our solar system and the most important question how was the water brought on Earth. Besides the MMX mothership (JAXA) which is responsible for sampling and sample return to Earth a small rover which is built by CNES and DLR shall land on Phobos for in-situ measurements similar to MASCOT (Mobile Asteroid Surface Scout) on Ryugu. The MMX rover is a four wheel driven autonomous system with a size of 41 cm x 37 cm x 30 cm and a weight of approx. 25 kg. Multiple science instruments and cameras are integrated in the rover body. The rover body is basically a rectangular box, attached at the sides are four legs with one wheel per leg. When the rover is detached from the mothership, the legs are folded together at the side of the rover body. When the rover has landed passively (no parachute, braking rockets) on Phobos, the legs are autonomously controlled to bring the rover in an upright orientation. One Phobos day lasts 7 earth hours, which gives for the total mission time of 3 earth months, the number of about 300 extreme temperature cycles. These cycles and the wide span of surface temperature between day and night are main design drivers for the rover. This paper gives a short overview on the MMX mission, the MMX rover and a detailed view on the development of the MMX rover locomotion subsystem

MMX Rover Locomotion Subsystem - Development and Testing towards the Flight Model

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 rove

Analyse der Kaltverschweißung von Metallseilen für die Verwendung in Weltraumroboterhänden

Um in Zukunft Astronauten bei ihren Aufgaben sicher und zuverlässig zu unterstützen müs-sen Robotersysteme entwickelt werden die in menschenfeindlichen Umgebungen, wie dem Weltraum, robust und ausdauernd sind. Zudem sollten diese als universelle Werkzeuge die-nen. In der Natur zeigt sich die menschliche Hand durch Bewältigung verschiedenster Greif-operationen als eines der universellsten Werkzeuge aus. Der Mensch ist jedoch nicht für die raue Umgebung des Weltalls geschaffen und muss deshalb durch geeignete Systeme dazu befähigt werden in solchen Umgebung zu überleben oder diese zu erkunden ohne wirklich vor Ort zu sein. Eine dieser Lösung wird mit der Spacehand des DLR vorangetrieben. Die Spacehand soll wie die menschliche Hand als universelles seilbetriebenes Werkzeug für die Astronauten dienen und durch diese telemanipuliert werden. Um die Funktionalität der Spacehand zu gewährleisten wird in dieser Arbeit untersucht wie sich die Aktuierung durch Stahlseile in Hinblick von Kaltverschweißungseffekten verhält. Hierzu wird in einer Ther-malvakuumkammer zunächst ein Prüfstand aufgebaut und verschiedene Szenarien untersucht. Die Prüfszenarien sollen darüber Aufschluss geben, ob und in welcher Stärke sich Kaltver-schweißungen an den Stahlseilen zeigen. Nach Beendigung der Testreihen erfolgen eine Be-wertung der Ergebnisse und eine anschließende Diskussion über die Eignung von Stahlseilen zur Verwendung in Weltraumroboterhänden bei Langzeitmissionen

Wheeled locomotion in milli-gravity: A technology experiment for the MMX Rover.

For the Martian Moons eXploration (MMX) mission of the Japan Aerospace Exploration Agency (JAXA), the French Centre National d'Études Spatiales (CNES) and the German Aerospace Center (DLR) jointly develop a wheeled exploration rover. This paper will discuss the planned analysis of wheeled locomotion of the MMX Rover. The focus will be on the expected challenges, the methods to overcome them and the plans on how to achieve a better understanding of wheeled locomotion in a milli-g environment by performing and analyzing a set of driving activities on Phobos. With the MMX Rover being the first wheeled system landing on a small body, there is no experience on how such a system will behave. Topography, rocks and regolith at the landing site will have a large impact on the achievable performance. To ensure safe operations, the locomotion system, developed at DLR-RMC, is designed to master a large variety of environments: The wheels are designed for optimal traction on soft regolith and the legs are actuated individually. Thereby, advanced maneuvers like inching locomotion allow the rover to climb slopes beyond its regular traction limits. In parallel to the hardware and software development, a detailed simulation environment was established, which both assists in the design of the rover and will serve as a planning tool during driving operations. During the mission, specific locomotion manoeuvres are performed and the downlinked data is then analyzed in detail to obtain a comprehensive understanding of the achieved performance and its constraints. The telemetry from the rover will be used to reconstruct the situation in simulation. After correlation, the simulator is used to get a deeper understanding of the wheeled locomotion dynamics under milli-g conditions. Of particular interest are the control strategies chosen and the influence of environmental characteristics on the rover's maneuverability, traction achieved, obstacle traversal, and controllability. Furthermore, the performance of specific components, like the traction generated by the wheels and the actuator performance, will be compared against expected behavior. During the mission, the findings will be directly used to improve the day-by-day planning of the rover's driving phases. Later, the results will be further analyzed and published to enable better designs with reduced uncertainties for future wheeled locomotion in low gravity environments. The paper will give details on the planned maneuvers, strategies to analyze them as well as the expected results

Qualification of the MMX Rover Locomotion Subsystem for the Martian Moon Phobos

Planetary rovers have proven their function and value for the Earth moon as well as Mars in the past decades. While these celestial bodies have a gravity of the same order of magnitude as the Earth, wheeled locomotion has never been performed on a body with much lower gravity. Within the Japanese Martian Moon eXploration (MMX) mission, a wheeled rover will land on the Martian Moon Phobos with a gravity of about 1/2000 of the Earth gravity. The Robotic and Mechatronics Center of the German Aerospace Center (DLR-RMC) has designed and built the locomotion subsystem (LSS) for this rover. As the first ever driving gear for milli-gravity, the LSS needed to undergo a comprehensive qualification campaign. Due to the very challenging timeline of this project, the extent of the campaign needed to be carefully tailored to the needs of the mission. This work describes the concept of the verification including some crucial tailoring choices that have been made. The individual domains of verification are then described in detail with their scope, setup, procedure and results. The goal of this publication is to give a good overview and a detailed insight into the verification of the LSS for milli-gravity. Besides follow-up missions to Phobos, this work is also a good foundation for the qualification of future driving gears for low gravity environments or small rovers in general