Fault Detection, Isolation and Recovery in the MMX Rover Locomotion Subsystem

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'études 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

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

Mobile Asteroid Surface Scout (MASCOT) - Design, Development and Delivery of a Small Asteroid Lander Aboard Hayabusa2

MASCOT is a small asteroid lander launched on December 3rd, 2014, aboard the Japanese HAYABUSA2 asteroid sample-return mission towards the 980 m diameter C-type near-Earth asteroid (162173) 1999 JU3. MASCOT carries four full-scale asteroid science instruments and an uprighting and relocation device within a shoebox-sized 10 kg spacecraft; a complete lander comparable in mass and volume to a medium-sized science instrument on interplanetary missions. Asteroid surface science will be obtained by: MicrOmega, a hyperspectral near- to mid-infrared soil microscope provided by IAS; MASCAM, a wide-angle Si CMOS camera with multicolour LED illumination unit; MARA, a multichannel thermal infrared surface radiometer; the magnetometer, MASMAG, provided by the Technical University of Braunschweig. Further information on the conditions at or near the lander‘s surfaces is generated as a byproduct of attitude sensors and other system sensors. MASCOT uses a highly integrated, ultra-lightweight truss-frame structure made from a CFRP-foam sandwich. It has three internal mechanisms: a preload release mechanism, to release the structural preload applied for launch across the separation mechanism interface; a separation mechanism, to realize the ejection of MASCOT from the semi-recessed stowed position within HAYABUSA2; and the mobility mechanism, for uprighting and hopping. MASCOT uses semi-passive thermal control with Multi-Layer Insulation, two heatpipes and a radiator for heat rejection during operational phases, and heaters for thermal control of the battery and the main electronics during cruise. MASCOT is powered by a primary battery during its on-asteroid operational phase, but supplied by HAYABUSA2 during cruise for check-out and calibration operations as well as thermal control. All housekeeping and scientific data is transmitted to Earth via a relay link with the HAYABUSA2 main-spacecraft, also during cruise operations. The link uses redundant omnidirectional UHF-Band transceivers and patch antennae on the lander. The MASCOT On-Board Computer is a redundant system providing data storage, instrument interfacing, command and data handling, as well as autonomous surface operation functions. Knowledge of the lander’s attitude on the asteroid is key to the success of its uprighting and hopping function. The attitude is determined by a threefold set of sensors: optical distance sensors, photo electric cells and thermal sensors. A range of experimental sensors is also carried. MASCOT was build by the German Aerospace Center, DLR, with contributions from the French space agency, CNES. The system design, science instruments, and operational concept of MASCOT will be presented, with sidenotes on the development of the mission and its integration with HAYABUSA2

Highly integrated, radiation-hardened, motor controller with phase current measurement

Robotic systems provide an excellent on-site or remote support for astronauts during routine tasks and perform increasingly complex autonomous tasks during exploration missions. New systems like the robotic arm CAESAR and the highly dexterous four fingered robotic hand Spacehand are designed in order to improve the skills and performance of the systems while the needed space for the electronics and the power consumption is decreasing. The small exploration systems MASCOT highlighted the need for a small form factor, highly integrated, lightweight but simultaneously a highly performance motor controller. This paper presents a cold redundant, three phase brushless DC motor driver for medium radiation environment which was developed at the Robotics and Mechatronics Center of the German Aerospace Center (DLR-RMC). The size efficiency of the proposed design relies on an extremely compact position sensing circuit which is based on a resolver principal. The integrated bridge driver, with current limitation, withstands a continuous power up to 120W. To simplify the design the internal voltages are limited to a minimum set. A fault-tolerant processor is used to guarantee a high reliability, The choice of several standard communication interfaces gives the user multiple possibilities to integrate the board in existing designs. The small form factor improves and simplifies the thermal management as well as the integration in small systems. The simple mechanical shape reduces the integrator effort and offers a large amount of configurations. The three phase current sensing, together with the high performance computation platform, allows the implementation of a high level current control such as field oriented control methods. Such control methods optimize the dynamic performance of the actuator, thus, leveraging the actuator performance to size ratio. The system uses a fully programmable processor unit, offering real-time communication and logging capabilities, fully integrated control loops and rich monitoring. This paper gives an overview of the requirements, discusses several of the keys aspects of the design and reports the current state of the design

A Dual Three-Phase DC-Link Inverter Prototype Powering a Redundant Space Robotics Motor Drive

Like their industrial counterparts, space robotics motor drives require a DC-link inverter to convert the spacecrafts DC-bus voltage into a three-phase AC rotating field. The designer of a space grade inverter needs to balance various opposed design objectives. Achieving a high level of operational reliability, including dependable fault monitoring capabilities is essential, while simultaneously keeping design complexity as low as possible. Based on the preliminary results of an earlier on-orbit-servicing project study initiated by German Aerospace Center DLR, the Institute of Robotics and Mechatronics has developed an engineering prototype of a robotic arm for space. This paper describes the design and initial operation of the robotic system's dual three-phase DC-link inverter, which powers the robotic motor drives. It summarizes some lessons learned during the development process and indicates the next steps required to further test and qualify the inverter for a planned in-orbit demonstration of European space robotics servicing technology

Development of a Mobility Drive Unit for Low Gravity Planetary Body Exploration

The 10 kg asteroid lander package MASCOT (mobile asteroid surface scout), developed by DLR, is a contribution to the JAXA Hayabusa-II mission, intended to be launched in 2014. MASCOT will provide in-situ surface science at several sites on the C-type asteroid 1999 JU3. An innovative hopping mechanism, developed at the Robotics and Mechatronics Center (RMC) in Oberpfaffenhofen, allows the lander to upright to nominal position for measurements as well as to relocate by hopping. The mechanism concept considers the uncertain and harsh environment conditions on the asteroid surface by using the impulse of an eccentric mass with all rotating parts completely inside the MASCOT structure. The paper gives an overview of the major development activities which lead to a new promising powerful and scalable drive system for low gravity planetary body exploration

Radiation test of a BLDC motor driver component

Robotic systems will become in the future of space exploration an important technology, whereby brushless motor drives are used for locomotion and manipulation. This paper presents the radiation test results of a COTS motor driver

Flexible Three Phase Brushless DC Motor Driver for medium radiation level

Robotic systems can provide an excellent on-site or remote support for astronauts during routine tasks and perform even autonomous tasks during exploration missions. New systems like the robotic arm CAESAR, the fourfingered robotic hand Spacehand, small exploration systems like MASCOT or several Pan-Tilt-Units on rovers emphasize the need for a highly integrated, high performance motor controller with a small foot print. This paper presents a three Phase brushless DC Motor Driver for medium radiation levels which was developed at the Institute of Robotics and Mechatronics of the German Aerospace Center (DLR). This module is able to withstand 120W of continuous motor power, offers interfaces for analogue and digital motor position measurements as well as a standard high level communication interface on a single board with an extremely small footprint. Due to its small footprint, multiple boards could be used within a robotic system to drive multiple motors synchronously. Simulations have been performed to show the increase in performance that can be achieved through the simultaneous motion of multiple actuators. A potential application is MASCOT-2 (Mobile Asteroid Surface sCOuT), which is analyzed as a case study to present the benefits of a multi-actuator system for relocation and attitude control in low-gravity environments