Design and Operational Elements of the Robotic Subsystem for the e.deorbit Debris Removal Mission

This paper presents a robotic capture concept that was developed as part of the e.deorbit study by ESA. The defective and tumbling satellite ENVISAT was chosen as a potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. A robotic capture concept was developed that is based on a chaser satellite equipped with a seven degrees-of-freedom dexterous robotic manipulator, holding a dedicated linear two-bracket gripper. The satellite is also equipped with a clamping mechanism for achieving a stiff fixation with the grasped target, following their combined satellite-stack de-tumbling and prior to the execution of the de-orbit maneuver. Driving elements of the robotic design, operations and control are described and analyzed. These include pre and post-capture operations, the task-specific kinematics of the manipulator, the intrinsic mechanical arm flexibility and its effect on the arm's positioning accuracy, visual tracking, as well as the interaction between the manipulator controller and that of the chaser satellite. The kinematics analysis yielded robust reachability of the grasp point. The effects of intrinsic arm flexibility turned out to be noticeable but also effectively scalable through robot joint speed adaption throughout the maneuvers. During most of the critical robot arm operations, the internal robot joint torques are shown to be within the design limits. These limits are only reached for a limiting scenario of tumbling motion of ENVISAT, consisting of an initial pure spin of 5 deg/s about its unstable intermediate axis of inertia. The computer vision performance was found to be satisfactory with respect to positioning accuracy requirements. Further developments are necessary and are being pursued to meet the stringent mission-related robustness requirements. Overall, the analyses conducted in this study showed that the capture and de-orbiting of ENVISAT using the proposed robotic concept is feasible with respect to relevant mission requirements and for most of the operational scenarios considered. Future work aims at developing a combined chaser-robot system controller. This will include a visual servo to minimize the positioning errors during the contact phases of the mission (grasping and clamping). Further validation of the visual tracking in orbital lighting conditions will be pursued

Utilizing Artificial Intelligence for Achieving a Robust Architecture for Future Robotic Spacecraft

This paper presents a novel failure-tolerant architecture for future robotic spacecraft. It is based on the Time and Space Partitioning (TSP) principle as well as a combination of Artificial Intelligence (AI) and traditional concepts for system failure detection, isolation and recovery (FDIR). Contrary to classic payload that is separated from the platform, robotic devices attached onto a satellite become an integral part of the spacecraft itself. Hence, the robot needs to be integrated into the overall satellite FDIR concept in order to prevent fatal damage upon hardware or software failure. In addition, complex dexterous manipulators as required for onorbit servicing (OOS) tasks may reach unexpected failure states, where classic FDIR methods reach the edge of their capabilities with respect to successfully detecting and resolving them. Combining, and partly replacing traditional methods with flexible AI approaches aims to yield a control environment that features increased robustness, safety and reliability for space robots. The developed architecture is based on a modular on-board operational framework that features deterministic partition scheduling, an OS abstraction layer and a middleware for standardized inter-component and external communication. The supervisor (SUV) concept is utilized for exception and health management as well as deterministic system control and error management. In addition, a Kohonen self-organizing map (SOM) approach was implemented yielding a real-time robot sensor confidence analysis and failure detection. The SOM features nonsupervized training given a typical set of defined world states. By compiling a set of reviewable three-dimensional maps, alternative strategies in case of a failure can be found, increasing operational robustness. As demonstrator, a satellite simulator was set up featuring a client satellite that is to be captured by a servicing satellite with a 7-DoF dexterous manipulator. The avionics and robot control were - ntegrated on an embedded, space-qualified Airbus e.Cube on-board computer. The experiments showed that the integration of SOM for robot failure detection positively complemented the capabilities of traditional FDIR methods

ROBOPS - Approaching a Holistic and Unified Interface Service Definition for Future Robotic Spacecraft

This paper describes a unified and holistic approach to the identification and definition of interface services and protocols for future robotic spacecraft. Hardware-in-the loop (HiL) demonstration results are outlined based on the implementation of selected end-to-end services. The developed communication interface is intended to facilitate the command, control and monitoring of classic satellites as well as attached robotic devices and robotic mobile platforms. Both system autonomy and distributed mission architectures are promoted. Based on an initial state-of-the-art review of current and past robotic space missions, required capabilities with respect to communication, levels of robotic control and autonomy were investigated. Thereof derived, a general categorization of possible robotic missions was developed, including the definition of roles, responsibilities and major use cases. By applying a hierarchical mission composition, a definition of functional classes and a classification of autonomy levels, a systematic and holistic categorization could be found to the definition of the required services. The concept can be applied to arbitrary hardware and deal as a standard for on-board, spacecraft-to-spacecraft and ground-spacecraft communication. Subsequently, suitable technologies for the definition and implementation of these services were analyzed and a conceptual architecture was developed. As underlying communication protocols and architectures, various options have been evaluated. A disruption-tolerant network (DTN)-based solution was chosen, however, the defined services can work over a variety of different communication protocols. For demonstration purposes, a subset was implemented within the METERON operations environment (MOE) [17] and demonstrated with two different robotic devices, a 7-degrees of freedom (DoF) dexterous manipulator and a samplecollecting rover mockup. The experiments showed that the developed architecture can successfully be used to control robotic manipulators and rovers over DTN in a standardized way

Robust and modular on-board architecture for future robotic spacecraft

This paper presents a novel approach for future robotic spacecraft by utilizing a modular and robust software architecture based on the time and space partitioning (TSP) concept. Classic satellites are characterized by a strict separation between platform and payload subsystems, both in hardware resources as well as in control software. Novel space-robotic applications such as on-orbit servicing (OOS) feature dexterous robotic devices attached onto the satellite that impose a direct physical feedback on their floating base. Through the high degree of interdependencies, the whole satellite turns into a space robot. Hence, the robot becomes an integral part of the spacecraft itself and needs to be integrated into the existing control and operations approach. The developed embedded on-board framework represents a modular and robust control and communication environment that allows both classic satellite as well as real-time and autonomous robotic operations. The framework features an integral fault detection, isolation and recovery (FDIR) concept in order to prevent overall system shutdown upon single-point failure. Single software components reside in separate logical modules, i.e. partitions, in order to avoid resource violations. Upon critical failure, partitions can be restarted without detracting the rest of the system. By applying explicit time scheduling of partitions, system resources can be optimally distributed and deterministic behavior be achieved. Core system functionality has been implemented by ECSS-tested components that are configurable and thus re-usable over multiple missions. As demonstrator, a realistic on-orbit servicing simulation was set up that comprises autonomous target satellite capture and fault management. The presented architecture follows an integrated approach that is required for safely operating future robotic spacecraft. Through re-usability of software components, fewer resources for the implementation and verification process are - equired as only additional, mission-specific components need to be taken care of. Application developers can use the core functionality and communication API and concentrate on their own task at hand

e.Deorbit Mission: OHB Debris Removal Concepts

To stabilize the space debris problem in low Earth orbit(LEO), the performance of active debris removalmissions is required. To prepare for such missions, theEuropean Space Agency (ESA) has initiated thee.Deorbit mission as part of its Clean Space activities,with ENVISAT as a sizing case for a potential removaltarget.For the phase A of e.Deorbit, OHB System has led ateam with strong heritage in the key fields of missiondesign, space robotics, and guidance, navigation andcontrol (GNC). In this paper, the mission concepts for removing spacedebris with a rigid or flexible capture mechanism arepresented. While re-orbiting was also studied, it is notaddressed in this paper.A key focus of the study has been the creation of a cost-effective design, allowing the high number of futureremoval missions needed for the stabilization ofthe space debris environment while not sacrificing thenecessary levels of reliability and safety

SPHERES Interact - Human–Machine Interaction aboard the International Space Station

The deployment of space robots for servicing and maintenance operations that are teleoperated from the ground is a valuable addition to existing autonomous systems, because it will provide flexibility and robustness in mission operations. In this connection, not only robotic manipulators are of great use, but also free-flying inspector satellites supporting the operations through additional feedback to the ground operator. The manual control of such an inspector satellite at a remote location is challenging, because navigation in three-dimensional space is unfamiliar and large time delays can occur in the communication channel. This paper shows a series of robotic experiments, in which free flyers are controlled by astronauts aboard the International Space Station (ISS). The Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) were utilized to study several aspects of a remotely controlled inspector satellite. The focus in this case study is investigating different approaches to human–spacecraft interaction with varying levels of autonomy under zero-gravity conditions

RobOps - Services for Telerobotic System Operations

This paper presents an approach towards the identification and definition of services for robotic operations. By analyzing use cases, scenarios and current robotic interfaces and operations and by taking autonomy concepts into account, a systematic categorization of robotic services is developed and used as a starting point for the definition of common and extendible robotic operation services. Suitable technologies for the definition and implementation of such services are analyzed and a conceptual architecture is presented. The on-going activities for the demonstration of these services with two different robotic systems are described

Tunable Gas Permeation Behavior in Self-Standing Cellulose Nanocrystal-Based Membranes

Biopolymers arise as environmentally benign alternatives to bio-accumulating, fossil resource-based synthetic polymers for a variety of applications, many of which require self-standing films or membranes. Novel sustainable amine-functionalized cellulose nanocrystals (CNCs) form dense films with low porosity suitable for gas barriers. Due to their brittleness, pure CNC membranes are challenging to work with but represent an attractive support material for selectivity-inducing additives. Supported ionic liquid membranes (SILMs) are promising due to their tunable properties and good performance in gas separation. In this study, we investigate the possibilities to realize such applications by applying glucose and ionic liquids (ILs) as additives with different functions in CNC-based membranes. By the choice of the plasticizer, the gas permeation behavior of the flexible self-standing films can be tuned from impermeable, using glucose as an additive, to permeable by addition of the ILs 1,3-dibutylimidazolium acetate and 1,3-ditetrahydrofurfurylimidazolium acetate. Tunability is also observed through the choice of the CNC source in the form of an inversed selectivity of the gas pair N2/O2, which was traceable to the CNCs’ source-specific properties. The contributions of the matrix and additive were analyzed by comparing CNC to chitosan membranes and considering gas solubilities and diffusivities. The obtained results underline the diversity and tunability of bio-derived functional materials