Development of an Emulated Free-Floating Environment for On-Earth Testing of Space Robots

The ability to perform experiments on space robotic systems within a laboratory setting is crucial to development and testing of satellites and space robots prior to launch. One of the most widely used techniques which recreate the on-orbit motion of space robots and targets is hardware-in-the-loop simulation. This method requires extensive knowledge of the space robot model dynamic parameters. This research proposes a method which uses force feedback to control a robotic platform on which the space robot is mounted. The robotic platform is driven in such a way that the gravity-compensated forces and torques at the mounting interface are nullified. This method requires minimal knowledge of the system model and dynamic parameters. In this thesis, simulations are performed on both two-dimensional and three-dimensional systems and experimental validation on a two-dimensional system is conducted for proof-of-concept

Modeling a Controlled-Floating Space Robot for In-Space Services: A Beginner’s Tutorial

Ground-based applications of robotics and autonomous systems (RASs) are fast advancing, and there is a growing appetite for developing cost-effective RAS solutions for in situ servicing, debris removal, manufacturing, and assembly missions. An orbital space robot, that is, a spacecraft mounted with one or more robotic manipulators, is an inevitable system for a range of future in-orbit services. However, various practical challenges make controlling a space robot extremely difficult compared with its terrestrial counterpart. The state of the art of modeling the kinematics and dynamics of a space robot, operating in the free-flying and free-floating modes, has been well studied by researchers. However, these two modes of operation have various shortcomings, which can be overcome by operating the space robot in the controlled-floating mode. This tutorial article aims to address the knowledge gap in modeling complex space robots operating in the controlled-floating mode and under perturbed conditions. The novel research contribution of this article is the refined dynamic model of a chaser space robot, derived with respect to the moving target while accounting for the internal perturbations due to constantly changing the center of mass, the inertial matrix, Coriolis, and centrifugal terms of the coupled system; it also accounts for the external environmental disturbances. The nonlinear model presented accurately represents the multibody coupled dynamics of a space robot, which is pivotal for precise pose control. Simulation results presented demonstrate the accuracy of the model for closed-loop control. In addition to the theoretical contributions in mathematical modeling, this article also offers a commercially viable solution for a wide range of in-orbit missions

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