MOSAR-WM: A relocatable robotic arm demonstrator for future on-orbit applications

In the past few years, the raise of space robotics yielded novel potential applications. The utilization of more advanced and capable robotic manipulators opens a whole new horizon of possibilities for future space missions, ranging from On-Orbit Servicing (OOS) of existing satellites (for refueling, Orbital replacement unit (ORU)or de-orbiting)to On-Orbit Assembly (OOA) and reconfiguration of modular spacecraft. This paper deals with the design and primary Manufacturing, Assembly, Integration and Testing (MAIT)activities of a novel robotic manipulator demonstrator for such on-orbit applications. MOSAR-WM is a 7 degree of freedom(DOF)manipulator, 1.6-meter long, symmetrical and relocatable (aka. “walking” capable). Its overall structure is human-like with asymmetric joints. Manipulator joints are hollow-shaft for internal cable routing, and include cutting-edge space-compatible technologies. Each joint embeds a torque sensor in addition to position sensors (incremental and absolute encoders). The kinematic architecture of MOSAR-WM offers a wide end effector workspace, and its stiff structure guarantees a high accuracy and repeatability while allowing compactness for launching and storing purposes. Each extremity of MOSAR-WM is equipped with a HOTDOCK standard interface that allows for mechanical connection, powering and controlling the arm. Manipulator avionics consists in seven joint controllers (one per joint) and an embedded computer called Walking manipulator controller(WMC) running a real time operating system. The WMC receives high-level commands from the external computing unit through the connected HOTDOCK interface. It also calculates the dynamic model of the robot to provide proper feed-forward terms for the joint control. Depending on the desired behaviour, the gains of the joint control loop are adaptive for optimal performance in position control. In addition, a Cartesian impedance control is implemented to allow for compliant operations. The joint controllers are daisy-chained through EtherCAT, while the control of each HOTDOCK is performed through a CAN bus managed by the internal WMC. MOSAR-WM is developed in the context of the European Commission’s Space Robotic H2020 MOSAR project. It aims to validate the developed technologies at Technology Readiness level (TRL)4 in a space representative scenario

HOTDOCK: Design and Validation of a New Generation of Standard Robotic Interface for On-Orbit Servicing

This paper presents the design and validation of HOTDOCK, a new generation of standard interface for on-orbit and planetary applications providing mechanical, power, data and thermal coupling capabilities between payloads and spacecraft, between spacecraft modules and as end-effector of robotic manipulators. The provision of standard interfaces in the design of spacecraft buses and payload modules will become essential to enable the emerging LEO/GEO on-orbit robotic servicing market. That includes payload management for spacecraft maintenance and reconfiguration, large structures assembly in space and de-orbiting operations. Standard interfaces are also highly interesting for supporting robotic operations in future deep space missions (LOP-G, Moon and Mars surface operations). HOTDOCK features a compact and fully integrated androgynous and 90-degree symmetrical design. The external form-fit geometry supports mating trajectories in a cone of up to 130-degrees, allowing for simultaneous connection of three orthogonally mounted interfaces. The unique patented coupling mechanism, along the circumference, allows stiff mechanical structural coupling with high load transfer. A central connection plate, equipped with spring-loaded POGO pin connectors, offers re-configurable and switchable electrical power as well as bi-directional high rate data transfer between connected subsystems. HOTDOCK can be optionally equipped with a fluidic transfer capability for thermal cooling on top of the regular thermal conduction between two units. In its nominal configuration called Active, HOTDOCK provides an actuation mechanism for the mating as well as integrated control and interface electronics. A purely passive version, without active components, has also been developed to offer a lower cost, volume and mass version. Both Active to Active and Active to Passive connections are possible, allowing in each case power, data and thermal transfer capabilities. HOTDOCK has been adopted as the reference Standard Interface in three projects of the European Commission’s H2020 Space Robotic Technologies cluster(OG8 PULSAR, OG9 MOSAR and OG11 PRO-ACT). They respectively address large structure assembly in space, modular satellite reconfiguration, and collaborative robotic planetary operations. More than 50units are currently being produced for integration in several ground demonstrators (TRL 4). Furthermore, HOTDOCK is used as part of the Michigan Technical University “T-REX” project awarded by NASA (BIG Idea Challenge)