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

Robotic Manipulation and Capture in Space: A Survey

Space exploration and exploitation depend on the development of on-orbit robotic capabilities for tasks such as servicing of satellites, removing of orbital debris, or construction and maintenance of orbital assets. Manipulation and capture of objects on-orbit are key enablers for these capabilities. This survey addresses fundamental aspects of manipulation and capture, such as the dynamics of space manipulator systems (SMS), i.e., satellites equipped with manipulators, the contact dynamics between manipulator grippers/payloads and targets, and the methods for identifying properties of SMSs and their targets. Also, it presents recent work of sensing pose and system states, of motion planning for capturing a target, and of feedback control methods for SMS during motion or interaction tasks. Finally, the paper reviews major ground testing testbeds for capture operations, and several notable missions and technologies developed for capture of targets on-orbit

ET-Class, an Energy Transfer-based Classification of Space Debris Removal Methods and Missions

Space debris is positioned as a fatal problem for current and future space missions. Many e ective space debris removal methods have been proposed in the past decade, and several techniques have been either tested on the ground or in parabolic ight experiments. Nevertheless, no uncooperative debris has been removed from any orbit until this moment. Therefore, to expand this research eld and progress the development of space debris removal technologies, this paper reviews and compares the existing technologies with past, present, and future methods and missions. Moreover, since one of the critical problems when designing space debris removal solutions is how to transfer the energy between the chaser/de-orbiting kit and target during the rst interaction, this paper proposes a novel classi cation approach, named ET-Class (Energy Transfer Class). This classi cation approach provides an energy-based perspective to the space debris phenomenon by classifying how existing methods dissipate or store energy during rst contact

Dynamics and control of robotic systems for on-orbit objects manipulation

Multi-body systems (MSs) are assemblies composed of multiple bodies (either rigid or structurally flexible) connected among each other by means of mechanical joints. In many engineering fields (such as aerospace, aeronautics, robotics, machinery, military weapons and bio-mechanics) a large number of systems (e.g. space robots, aircraft, terrestrial vehicles, industrial machinery, launching systems) can be included in this category. The dynamic characteristics and performance of such complex systems need to be accurately and rapidly analyzed and predicted. Taking this engineering background into consideration, a new branch of study, named as Multi-body Systems Dynamics (MSD), emerged in the 1960s and has become an important research and development area in modern mechanics; it mainly addresses the theoretical modeling, numerical analysis, design optimization and control for complex MSs. The research on dynamics modeling and numerical solving techniques for rigid multi-body systems has relatively matured and perfected through the developments over the past half century. However, for many engineering problems, the rigid multi-body system model cannot meet the requirements in terms of precision. It is then necessary to consider the coupling between the large rigid motions of the MS components and their elastic displacements; thus the study of the dynamics of flexible MSs has gained increasing relevance. The flexible MSD involves many theories and methods, such as continuum mechanics, computational mechanics and nonlinear dynamics, thus implying a higher requirement on the theoretical basis. Robotic on-orbit operations for servicing, repairing or de-orbiting existing satellites are among space mission concepts expected to have a relevant role in a close future. In particular, many studies have been focused on removing significant debris objects from their orbit. While mission designs involving tethers, nets, harpoons or glues are among options studied and analyzed by the scientific and industrial community, the debris removal by means of robotic manipulators seems to be the solution with the longest space experience. In fact, robotic manipulators are now a well-established technology in space applications as they are routinely used for handling and assembling large space modules and for reducing human extravehicular activities on the International Space Station. The operations are generally performed in a tele-operated approach, where the slow motion of the robotic manipulator is controlled by specialized operators on board of the space station or at the ground control center. Grasped objects are usually cooperative, meaning they are capable to re-orient themselves or have appropriate mechanisms for engagement with the end-effectors of the manipulator (i.e. its terminal parts). On the other hand, debris removal missions would target objects which are often non-controlled and lacking specific hooking points. Moreover, there would be a distinctive advantage in terms of cost and reliability to conduct this type of mission profile in a fully autonomous manner, as issues like obstacle avoidance could be more easily managed locally than from a far away control center. Space Manipulator Systems (SMSs) are satellites made of a base platform equipped with one or more robotic arms. A SMS is a floating system because its base is not fixed to the ground like in terrestrial manipulators; therefore, the motion of the robotic arms affects the attitude and position of the base platform and vice versa. This reciprocal influence is denoted as "dynamic coupling" and makes the dynamics modeling and motion planning of a space robot much more complicated than those of fixed-base manipulators. Indeed, SMSs are complex systems whose dynamics modeling requires appropriate theoretical and mathematical tools. The growing importance SMSs are acquiring is due to their operational ductility as they are able to perform complicated tasks such as repairing, refueling, re-orbiting spacecraft, assembling articulated space structures and cleaning up the increasing amount of space debris. SMSs have also been employed in several rendezvous and docking missions. They have also been the object of many studies which verified the possibility to extend the operational life of commercial and scientific satellites by using an automated servicing spacecraft dedicated to repair, refuel and/or manage their failures (e.g. DARPA's Orbital Express and JAXA's ETS VII). Furthermore, Active Debris Removal (ADR) via robotic systems is one of the main concerns governments and space agencies have been facing in the last years. As a result, the grasping and post-grasping operations on non-cooperative objects are still open research areas facing many technical challenges: the target object identification by means of passive or active optical techniques, the estimation of its kinematic state, the design of dexterous robotic manipulators and end-effectors, the multi-body dynamics analysis, the selection of approaching and grasping maneuvers and the post-grasping mission planning are the main open research challenges in this field. The missions involving the use of SMSs are usually characterized by the following typical phases: 1. Orbital approach; 2. Rendez-vous; 3. Robotic arm(s) deployment; 4. Pre-grasping; 5. Grasping and post-grasping operations. This thesis project will focus on the last three. The manuscript is structured as follows: Chapter 1 presents the derivation of a multi-body system dynamics equations further developing them to reach their Kane's formulation; Chapter 2 investigates two different approaches (Particle Swarm Optimization and Machine Learning) dealing with a space manipulator deployment maneuver; Chapter 3 addresses the design of a combined Impedance+PD controller capable of accomplishing the pre-grasping phase goals and Chapter 4 is dedicated to the dynamic modeling of the closed-loop kinematic chain formed by the manipulator and the grasped target object and to the synthesis of a Jacobian Transpose+PD controller for a post-grasping docking maneuver. Finally, the concluding remarks summarize the overall thesis contribution

Space Debris as an international safety issue. Case studies in active removing techniques.

Η παρούσα διπλωματική εργασία πραγματοποιήθηκε υπό την αιγίδα του Τμήματος Πληροφορικής & Τηλεπικοινωνιών του Εθνικού και Καποδιστριακού Πανεπιστημίου Αθηνών για το Μεταπτυχιακό Πρόγραμμα Σπουδών «Διαστημικές Τεχνολογίες, Εφαρμογές και Υπηρεσίες». Στόχος της διατριβής ήταν να αναδείξει τη σημασία της έγκαιρης ανάληψης δράσης σε διεθνές επίπεδο, ώστε το ζήτημα των διαστημικών υπολειμμάτων να μην γίνει μείζονα απειλή κατά των επιχειρησιακών διαστημικών συστημάτων και των ανθρώπων που βρίσκονται σε τροχιά γύρω από τη γη. Παρόλο που το θέμα των διαστημικών υπολειμμάτων έχει απασχολήσει τον επιστημονικό, τεχνολογικό και πολιτικό κόσμο σχεδόν από την απαρχή της διαστημικής εποχής, δεν έχει ακόμα βρεθεί ουσιαστική λύση ούτε σε επιστημονικό, ούτε σε τεχνολογικό, ούτε σε πολιτικό επίπεδο. Στα παρακάτω κεφάλαια γίνεται μια ανάλυση του προβλήματος των διαστημικών υπολειμμάτων και αναφέρονται τα τεχνολογικά, νομικά και οικονομικά εμπόδια που παρουσιάζονται σε μια προσπάθεια απομάκρυνσης διαστημικών υπολειμμάτων. Στη συνέχεια αναπτύσσεται η έννοια της ασφάλειας στο διάστημα και πώς αυτή επηρεάζεται από την ύπαρξη διαστημικών υπολειμμάτων. Ταυτόχρονα γίνεται μια ανάλυση του ρίσκου που διέπει τις διαστημικές αποστολές, τόσο σε επίπεδο συστημάτων, όσο και σε επίπεδο ανθρώπινης ζωής σε συνάρτηση με την αύξηση των διαστημικών υπολειμμάτων. Από την ανάλυση αυτή δεικνύεται ότι η αύξηση των διαστημικών υπολειμμάτων λόγω περισσότερων διαστημικών αποστολών, καθώς και το ξεκίνημα της εποχής του διαστημικού τουρισμού, θα αποτελέσει έναν ισχυρό παράγοντα κινδύνου εάν δεν παρθούν άμεσα μέτρα. Στη συνέχεια παρουσιάζονται, σε τεχνικό επίπεδο, οι δυνατότητες εντοπισμού και παρατήρησης των διαστημικών υπολειμμάτων, καθώς και οι προοπτικές αυτών των συστημάτων. Επιπλέον, γίνεται αναφορά στο ποιες θα είναι οι μελλοντικές απαιτήσεις εντοπισμού και παρατήρησης των διαστημικών υπολειμμάτων ώστε να είναι αποτελεσματικές οι αποστολές απομάκρυνσης διαστημικών υπολειμμάτων. Συνεχίζοντας, παρουσιάζονται οι κύριες τεχνικές ενεργητικής απομάκρυνσης διαστημικών υπολειμμάτων, όπως αυτές μελετώνται και κατασκευάζονται από διαστημικούς οργανισμούς και διαστημικές εταιρείες. Τέλος, διενεργείται μια συγκριτική μελέτη των τεχνικών απομάκρυνσης διαστημικών υπολειμμάτων μέσω βαθμολόγησης τεσσάρων κύριων κριτηρίων και παρουσιάζεται ως αποτέλεσμα μια υπόθεση βέλτιστης τεχνολογίας απομάκρυνσης διαστημικών υπολειμμάτων. Από τη ανάλυση της Διπλωματικής Εργασίας γίνεται αντιληπτή η σημαντικότητα του να ληφθούν άμεσα αποφάσεις και να γίνουν οι κατάλληλες ενέργειες, ώστε τα διαστημικά υπολείμματα να μην αποτελέσουν κύριο παράγοντα κινδύνου για την ανθρωπότητα όπως τη γνωρίζουμε σήμερα.This thesis was conducted under the umbrella of the Department of Informatics & Telecommunication of the National and Kapodistrian University of Athens for the Postgraduate Program “Space Technologies, Applications and Services”. The aim of the thesis was to highlight the significance of taking timely action in an international level, for the space debris issue not to become a major threat against the operational space systems and the humans orbiting earth. Although the issue of space debris has occupied the scientific, technological and political world almost since the beginning of the space era, no substantial solution has yet been found either at a scientific, technological or political level. The following chapters provide an analysis of the space debris problem and present the technological, legal, and financial barriers to an effort to remove space debris. Then, the concept of security in space and the way it is affected by the existence of space debris is developed. At the same time, an analysis of the risk that governs space missions, both at the level of operation of space systems and at the level of human life in relation to the increase in space debris, is conducted. This analysis shows that the increase in space debris due to more space missions, as well as the onset of the era of space tourism, will be a strong risk factor if immediate measures are not taken. Then, at a technical level, the possibilities of locating and tracking space debris are presented, as well as the prospects of these technical systems. In addition, the future requirements for space debris detection and tracking, for space debris removal missions to be effective, are presented. Additionally, the main active space debris removal techniques studied and developed by space agencies and space companies are presented. Finally, a comparative study of space debris removal techniques is conducted by scoring four main criteria and a hypothesis of an optimal space debris removal technology is presented as a result. The analysis of the thesis shows the importance of making immediate decisions and taking the appropriate actions so that space debris does not constitute a major risk factor for humanity as we know it today

Space Debris Mitigation CONOPS Development

Space debris remains an unsolved hazard for space operators and astronomers alike. Passive debris mitigation techniques have been enumerated and codified by the UNCOPUOS and IADC and several proposals for actively mitigating space debris have been presented. However, the space debris problem requires reframing. On the way to developing a viable CONOPS, a multi-disciplinary construct for building solution sets to tackle the space debris problem must be created. It must be shaped by building blocks of active and passive debris mitigation techniques, debris characterization and law. Central considerations must be taken. First, targeting of space debris for removal must be prioritized to unite effort and to make significant reductions in the space debris threat. Next, a leading agent must be identified and empowered to act as an executor for a space debris mitigation program, passive or active. Also needed is enactment of enforcement measures to ensure space faring nations comply with binding regulations. Lastly, active space debris mitigation programs must be urged along by the international community with contributions from all nations. Aside from monetary contributions, aid can be rendered via intellectual space and manpower. We must seek the right questions to effectively solve the space debris problem

Hybrid-Compliant System for Soft Capture of Uncooperative Space Debris

Active debris removal (ADR) is positioned by space agencies as an in-orbit task of great importance for stabilizing the exponential growth of space debris. Most of the already developed capturing systems are designed for large specific cooperative satellites, which leads to expensive one-to-one solutions. This paper proposed a versatile hybrid-compliant mechanism to target a vast range of small uncooperative space debris in low Earth orbit (LEO), enabling a profitable one-to-many solution. The system is custom-built to fit into a CubeSat. It incorporates active (with linear actuators and impedance controller) and passive (with revolute joints) compliance to dissipate the impact energy, ensure sufficient contact time, and successfully help capture a broader range of space debris. A simulation study was conducted to evaluate and validate the necessity of integrating hybrid compliance into the ADR system. This study found the relationships among the debris mass, the system’s stiffness, and the contact time and provided the required data for tuning the impedance controller (IC) gains. This study also demonstrated the importance of hybrid compliance to guarantee the safe and reliable capture of a broader range of space debris

Modeling and Control of a Flexible Space Robot to Capture a Tumbling Debris

RÉSUMÉ La conquête spatiale des 60 dernières années a généré une grande quantité d’objets à la dérive sur les orbites terrestres. Leur nombre grandissant constitue un danger omniprésent pour l’exploitation des satellites, et requiert aujourd’hui une intervention humaine pour réduire les risques de collision. En effet, l’estimation de leur croissance sur un horizon de 200 ans, connue sous le nom de “syndrôme de Kessler”, montre que l’accès à l’Espace sera grandement menacé si aucune mesure n’est prise pour endiguer cette prolifération. Le scientifique J.-C. Liou de la National Aeronautics and Space Administration (NASA) a montré que la tendance actuelle pourrait être stabilisée, voire inversée, si au moins cinq débris massifs étaient désorbités par an, tels que des satellites en fin de vie ou des étages supérieurs de lanceur. Parmi les nombreux concepts proposés pour cette mission, la robotique s’est imposée comme une des solutions les plus prometteuses grâce aux retours d’expérience des 30 dernières années. La Station Spatiale Internationale (ISS) possède déjà plusieurs bras robotiques opérationnels, et de nombreuses missions ont démontré le potentiel d’un tel système embarqué sur un satellite. Pour deux d’entre elles, des étapes fondamentales ont été validées pour le service en orbite,et s’avèrent être similaires aux problématiques de la désorbitation des débris. Cette thèse se concentre sur l’étape de capture d’un débris en rotation par un bras robotique ayant des segments flexibles. Cette phase comprend la planification de trajectoire et le contrôle du robot spatial, afin de saisir le point cible du débris de la façon la plus délicate possible. La validation des technologies nécessaires à un tel projet est quasiment impossible sur Terre, et requiert des moyens démesurés pour effectuer des essais en orbite. Par conséquent, la modélisation et la simulation de systèmes multi-corps flexibles est traitée en détails, et constitue une forte contribution de la thèse. À l’aide de ces modèles, une validation mixte est proposée par des essais expérimentaux, en reproduisant la cinématique en orbite par des manipulateurs industriels contrôlés par une simulation en temps réel. En résumé, cette thèse est construite autour des trois domaines suivants : la modélisation des robots spatiaux, le design de lois de contrôle, et leur validation sur un cas test. Dans un premier temps, la modélisation de robots spatiaux en condition d’apesanteur est développée pour une forme “en étoile”.----------ABSTRACT After 60 years of intensive satellite launches, the number of drifting objects in Earth orbits is reaching a shifting point, where human intervention is becoming necessary to reduce the threat of collision. Indeed, a 200 year forecast, known as the “Kessler syndrome”, states that space access will be greatly compromised if nothing is done to address the proliferation of these debris. Scientist J.-C. Liou from the National Aeronautics and Space Administration (NASA) has shown that the current trend could be reversed if at least five massive objects, such as dead satellites or rocket upper stages, were de-orbited each year. Among the various technical concepts considered for debris removal, robotics has emerged, over the last 30 years, as one of the most promising solutions. The International Space Station (ISS) already possesses fully operational robotic arms, and other missions have explored the potential of a manipulator embedded onto a satellite. During two of the latter, key capabilities have been demonstrated for on-orbit servicing, and prove to be equally useful for the purpose of debris removal. This thesis focuses on the close range capture of a tumbling debris by a robotic arm with light-weight flexible segments. This phase includes the motion planning and the control of a space robot, in order to smoothly catch a target point on the debris. The validation of such technologies is almost impossible on Earth and leads to prohibitive costs when performed on orbit. Therefore, the modeling and simulation of flexible multi-body systems has been investigated thoroughly, and is likewise a strong contribution of the thesis. Based on these models, an experimental validation is proposed by reproducing the on-orbit kinematics on a test bench made up of two industrial manipulators and driven by a real-time dynamic simulation. In a nutshell, the thesis is built around three main parts: the modeling of a space robot, the design of control laws, and their validation on a test case. The first part is dedicated to the flexible modeling of a space robot in conditions of weightlessness. A “star-shaped” multi-body system is considered, meaning that the rigid base carries various flexible appendages and robotic arms, assumed to be open mechanical chains only. The classic Newton-Euler and Lagrangian algorithms are brought together to account for the flexibility and to compute the dynamics in a numerically efficient way. The modeling step starts with the rigid fixed-base manipulators in order to introduce the notations, then, détails the flexible ones, and ends with the moving-base system to represent the space robots

Fault-tolerant feature-based estimation of space debris motion and inertial properties

The exponential increase of the needs of people in the modern society and the contextual development of the space technologies have led to a significant use of the lower Earth’s orbits for placing artificial satellites. The current overpopulation of these orbits also increased the interest of the major space agencies in technologies for the removal of at least the biggest spacecraft that have reached their end-life or have failed their mission. One of the key functionalities required in a mission for removing a non-cooperative spacecraft is the assessment of its kinematics and inertial properties. In a few cases, this information can be approximated by ground observations. However, a re-assessment after the rendezvous phase is of critical importance for refining the capture strategies preventing accidents. The CADET program (CApture and DE-orbiting Technologies), funded by Regione Piemonte and led by Aviospace s.r.l., involved Politecnico di Torino in the research for solutions to the above issue. This dissertation proposes methods and algorithms for estimating the location of the center of mass, the angular rate, and the moments of inertia of a passive object. These methods require that the chaser spacecraft be capable of tracking several features of the target through passive vision sensors. Because of harsh lighting conditions in the space environment, feature-based methods should tolerate temporary failures in detecting features. The principal works on this topic do not consider this important aspect, making it a characteristic trait of the proposed methods. Compared to typical v treatments of the estimation problem, the proposed techniques do not depend solely on state observers. However, methods for recovering missing information, like compressive sampling techniques, are used for preprocessing input data to support the efficient usage of state observers. Simulation results showed accuracy properties that are comparable to those of the best-known methods already proposed in the literature. The developed algorithms were tested in the laboratory staged by Aviospace s.r.l., whose name is CADETLab. The results of the experimental tests suggested the practical applicability of such algorithms for supporting a real active removal mission