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

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

Efficient Implementation of On-Chip Communication Optimized for SpaceWire Networks

SpaceWire has been used successfully as commu- nication backbone implemented on Field Programmable Gate Arrays (FPGAs) in several robotic systems at the DLR. However, the growing number of available System-on-Chip (SoC) solutions with integrated programmable logic and the demand for efficient processing power in embedded systems require high speed On- Chip communication. Using SpaceWire as interconnection bus inside FPGAs has a major drawback compared to dedicated On-Chip bus systems. As it is not designed to exploit the wide parallelism of FPGAs, several On-Chip communication standards outperform SpaceWire in terms of bandwidth and resource costs. Examples are the AMBA AXI bus, the Avalon bus, CoreConnect or the Wishbone SoC Interconnection. In this work, the Wishbone standard is used to show, how an FPGA system connected to a SpaceWire network can benefit from a dedicated On-Chip bus. The architecture of the Wishbone standard allows an almost seamless integration into a SpaceWire network. Essential parts of SpaceWire, like package oriented communication or time- code distribution, can be mapped onto the Wishbone standard. A slim protocol is presented to allow accessing the On-Chip address space from the SpaceWire network and vice versa. It is also shown, that a heterogeneous On-Chip network consisting of SpaceWire and Wishbone occupies less resources on an FPGA than a similar network implemented with SpaceWire only. In the future, this approach can be used to integrate SoCs with built-in programmable logic into a SpaceWire network

Using SpaceWire Time-codes for Global Synchronization of PLL-Based Local Clocks

Abstract In a control application all sensors and actuators have to be able to perform their functions in a specific time to guarantee the desired control cycle. To achieve an exact actual system state a synchronization of the different sensor measurements is necessary. This guarantees that all acquired values are in a very small period of time and not spread over the whole control cycle. Otherwise, a noiser system state would result. The simplest way to synchronize those measurements is with cyclic triggering. This can be either an external request via communication or generated locally by a timer. Both approaches work well in a monolithic system approach with a central unit due to the existence of a common clock domain. However, a distributed system consists of multiple monolithic systems connected via communication, each with a separate clock domain. Due to the communication delay from unit to unit, and the differences between the local clocks, a synchronization according to the presented approaches is only possible by introducing a global clock domain. With time-codes SpaceWire already includes a mechanism to distribute time over a network. However, the communication delay regarding the time-code distribution is not considered. In systems consisting of large networks which have to be synchronized in very small cycles (e.g. high dynamic robots see [1]) this aspect is not negligible. This approach introduces a global time distribution by synchronization and runtime compensation. The synchronization is based on digital phase locked loops (PLLs) which align the units’ local time to the occurence of SpaceWire time-codes. The runtime compensation of the time- code distribution in the network is based on statistical evaluation

SpaceWire Meets Big Data - Realtime Data Mining

Abstract —The whole is more than the sum of its parts. This saying particularly fits in the context of big data and data mining. A single data set is only valid and relevant at exactly one point in time. Dependencies between the individual elements of the data set as well as the behaviour over time can only be investigated if large amounts of data are available. A good example is traffic monitoring based on GPS data, WiFi, and/or cellular triangulation of modern mobile phones (see [1], [2]). Here, the data sets are collected from multiple sources to estimate a precise traffic situation. Data completeness is vital to achieving sufficient reflection of the actual state of a system, since information can be lost through downsampling. This is a difficult requirement to fulfill especially for highly dynamic systems like robots. Data recording over the same communication infrastructure from multiple sources must meet strict real time requirements of the control application. Main control loops at joint level of ≥ 3 kHz and up to 100 kHz at motor control are quite common (e.g. [3]). Due to this, a simple duplication of the cyclic data sets at CPU-level for simultaneously controlling and recording is not possible without decimation of the recording sample rate. Therefore recording has to be performed at a different point of the communication infrastructure. This approach provides a duplication of the data at SpaceWire packet level by using seperate SpaceWire regions for control and recording without violating the real time requirements of the control application

Robot Integrated User Interface for Physical Interaction with the DLR MIRO in Versatile Medical Procedures

To enhance the capability of the DLR MIRO for physical human robot interaction (pHRI), six buttons were integrated as additional input interface along the robot structure. A ring of eight RGB-LEDs at the instrument interface informs the user as additional output interface about the robot's state. The mechatronic design, which is transferable to other robots, adapts to the existing communication infrastructure of the robot and therefore offers real-time capability. Besides the interaction with the robot itself, it also allows the control of third party devices connected to its communication network. Both interfaces can be flexibly programmed e.g. in C++ or Simulink

Robotic Demands on On-Board Data Processing

This paper gives an overview of the control and computing architectures of current lightweight robots and their demands on on board data processing units. On Earth, robots are an established technology in our daily life. They are getting more and more aware of their surroundings, which allows their use in many new domains. Collaborative workplaces where a robotic co-worker directly interacts with a human are already state of the art. Current research on machine learning and Artificial Intelligence (AI) in the robotic domain will introduce many new applications for robotic systems. These developments also have a great potential to be used in future space missions, for example on-orbit servicing of satellites or maintenance of space stations. However, this induces certain requirements on involved computing hardware that future on-board data processing units will also have to deal with