Search

Hinfinity/μ methods are commonly used in Airbus Defence and Space for the design and validation of control solutions. Formulated in a worst-case paradigm, these methods necessarily lead to overly conservative solutions since sized on the extreme cases. However, the acceptance for relaxed control performances requires mastering the risk associated to the detected unlikely events calling for probabilistic performances metrics in the validation process. A probabilistic μ-analysis method is presented in this paper to exhaustively explore the uncertain parametric domain while evaluating the cumulative probability density function of the performance index. Recent μ-analysis tools implemented in the ONERA’s SMAC toolbox are coupled with a dichotomic search algorithm in order to delimit the safe parametric domain while incrementing the probability of success of criteria. The proposed algorithm is applied to a didactic second order system to demonstrate the performances of the method.

Pointing performances are always more demanding for the scientific and observation Space missions of the future generation. A deep study of all the possible micro-vibration sources therefore results mandatory. This article presents several tools to analyze and control the micro-perturbations induced by a Solar Array Drive Mechanism (SADM) on a spacecraft. A first tool allows the user to build the dynamic model of a spacecraft composed of different flexible appendages attached to the main body by revolute joints. A second tool provides the SimScape model of a SADM that is interfaced with the spacecraft dynamics and allows analyzing the mission pointing performances. Time and frequency studies can be performed to deeply investigate pointing performances in presence of vibrations. An example that shows the interest of the proposed tools is provided. An observation spacecraft with two flexible solar arrays and an antenna is studied. The pointing metrics are computed for two complementary solutions to the micro-vibration issue: a microstepping technique for the SADM driver and a Fast Steering Mirror (FSM) for the active control of the Line of Sight (LOS).

The works presented in this thesis deals with the design of robust model-based Fault Detection and Isolation (FDI) systems for space vehicles. The research work draws expertise from actions undertaken within a project at european level, which develops a collaborative effort between Bordeaux University, the European Space Agency and EADS Astrium Space Transportation on innovative and robust strategies for Reusable Launch Vehicles autonomy. A practical and relevant framework providing "high level" operator tuning parameters and covering the complete design-analysis cycle is proposed to solve the diagnosis problem. A prior trimmability analysis is also proposed to select and model actuator faulty scenarios for which the remaining healthy control effectors are able to maintain the vehicle around its flight trajectory. Formulated and managed in a min/max-type optimisation problem, the residual generator is finally obtained by solving a Semi Definite Programming problem and consists of a dynamic filter and two structuration matrices in charge of merging optimally the available onboard measurements and control signals. The design stage is followed by an original and specific diagnosis-oriented analysis phase, based on the calculation of the generalized structured singular value. The latter provides a necessary and suficient condition for the robustness and fault sensitivity achievement and allows, if need be, the user to get a clear idea of how the design trade-offs should be re-tuned to get as close as possible to the required performance levels. The proposed methodology is applied to diagnose fault occuring on the HL20 lifting body vehicle wing flaps during the Terminal Area Energy Management and Auto-Landing phases., Les travaux présentés dans ce mémoire s'inscrivent dans le cadre d'un projet de dimension européenne réalisé en partenariat avec l'Agence Spatiale Européenne et EADS Astrium sur le développement d'algorithmes innovants et robustes de diagnostic de pannes pour les véhicules spatiaux. Un cadre méthodologique générique et structuré offrant des paramètres de réglage de haut niveau et couvrant le cycle complet synthèse-analyse est proposé pour formuler et résoudre le problème de diagnostic. En outre, une étude préalable de trimmabilité statique permettant d'identifier et de caractériser des situations défaillantes non déstabilisantes, potentiellement compensables, et pour lesquelles la mise en place d'actions de reconfiguration permettrait de maintenir l'appareil sur sa trajectoire de vol est présentée. Formulé et géré dans un contexte multi-objectifs de type min/max, le problème de synthèse est résolu par utilisation des techniques d'optimisation LMI et fournit d'une part, les filtres de diagnostic et d'autre part, deux matrices d'allocation en charge de faire fusionner de façon optimale les signaux de mesure et de commande disponibles pour former le vecteur de résidus. L'étape d'analyse est effectuée par évaluation de la valeur singulière structurée généralisée mu_g dont les résultats permettent de conclure à la fois sur l'atteinte des objectifs, ou le cas échéant, de fournir des indications sur la manière dont les contraintes et/ou objectifs peuvent être relaxés ou modifiés. La méthodologie proposée est appliquée au diagnostic des pannes d'actionneurs du véhicule de rentrée atmosphérique HL20 lors des phases de dissipation d'énergie en zone terminale et d'atterrissage automatique.

International audience; This paper is devoted to H ∞ analysis and synthesis conditions of state-feedback periodic memory controllers, in the framework of periodic uncertain discrete-time systems. The proposed conditions are such that the user is allowed to freely add degrees-of-freedom to the control law which effectively reduces the conservatism of the synthesis condition and decreases the guaranteed H ∞ induced norm of the obtained uncertain closed-loop systems. Numerical examples show that for a particular structure of controllers the efficiency of the design theorem can be significantly enhanced by relaxing the structure of slack-variables.

International audience; Particularly attractive for small satellites, the use of magnetic torquers for attitude control is still a difficult problem. Indeed, equations are naturally time-varying and suffers from controllability issues. In this paper, a generic model, taking different kinds of pointing and different kinds of actuators into account, is proposed, linearized and then discretized. Recent studies demonstrate how combining magnetorquers and reaction wheels is attractive. Following this line, latest LMI synthesis techniques for static periodic controller are applied in this paper to the attitude control problem of a spacecraft equipped with both actuation systems. Simulation results are provided, showing the performance of the obtained control law.

SICVER is the French acronym of a collaborative research project, started in October 2006, and funded by ESA, ASTRIUM Space Transportation and the Regional Council of Aquitaine (France). This project is driven by IMS-LAPS, University Bordeaux 1 and is part of the VER/VEP project, supported by the Aerospace Valley cluster. SICVER aims at developing “Innovative Fault Detection, Isolation and Reconfiguration (FDIR) Strategies for Experimental Re-entry Vehicles”. The project includes two research areas. The first one deals with the design of a fault-tolerant on-board path planner ensuring a high level of spacecraft autonomy. The goal is to help the ground-level operations and to improve decision making. The second part deals with the design of an on-board fault diagnosis system dedicated to the detection and isolation of any relevant actuator fault which may occur during an atmospheric re-entry mission and which could lead to flight performance degradations. The FDIR module acts as a supervisory layer which manages all or a part of the GNC chain during the re-entry mission in order to assign a level of operational and/or decisional autonomy to the vehicle. Such a level of autonomy can be reached first by monitoring the vehicle behaviour, then by reconfiguring all or a part of the G&C chain when a faulty scenario occurs.

Next generation satellite missions will have to meet extremely challenging pointing stability requirements. Even low levels of vibration can introduce enough jitter in the optical elements to cause a significant reduction in image quality. The success of these projects is therefore constrained by the ability of on-board vibration isolation and optical control techniques to keep stable the structural elements of the spacecraft in the presence of external and internal disturbances.In this context, the research work presented in this thesis combines the expertise of the European Space Agency (ESA), the industry (Airbus Defence and Space) and the IMS laboratory (laboratoire de l’Intégration du Matériau au Système) with the aim of developing new generation of robust microvibration isolation systems for future space observation missions. More precisely, the thesis presents the development of an Integrated Modeling, Control and Analysis framework in which to conduct advanced studies related to reaction wheel microvibration mitigation.The thesis builds upon the previous research conducted by Airbus Defence and Space and ESA on the use of mixed active/passive microvibration mitigation techniques and provides a complete methodology for the uncertainty modeling, robust control system design and worst-case analysis of such systems for a typical satellite observation mission. It is shown how disturbances produced by mechanical spinning devices such as reaction wheels can be significantly attenuated in order to improve the pointing stability of the spacecraft even in the presence of model uncertainty and other nonlinear phenomenon.Finally, the work introduces a new disturbance model for the multi harmonic perturbation spectrum produced by spinning reaction wheels that is suitable for both controller synthesis and worst-case analysis using modern robust control tools. This model is exploited to provide new ways of simulating the image distortions induced by such disturbances.; Le contexte général des travaux de recherche de cette thèse concerne les problématiques liées à l’optimisation glob-ale liée à la conception des futurs satellites d’observation terrestre et de missions scientifiques, nécessitantune très haute stabilité en pointage (capacité du satellite à garder son point de visée). Plus particulièrement,les travaux concernent le contrôle actif des modes micro-vibratoires.Dans une mission satellitaire d’observation terrestre, la qualité des images dépend bien évidemmentdes instruments de mesure optique (diamètre du miroir, aberrations optiques et qualité du polissage)mais également des performances de la stabilité de la ligne de visée du satellite qui peut s’avérer dégradéepour cause de micro-vibrations. La présence de ces micro-vibrations est liée aux divers éléments tournantdu satellite tels que les mécanismes de rotation des panneaux solaires ou de contrôle d’orientation dusatellite (on parle de contrôle d’attitude réalisé au moyen de roues inertielles).Le contrôle des micro-vibrations représentent ainsi un défit technologique, conduisant l’ESA et les ac-teurs industriels du monde spatial, a considéré cette problématique comme hautement prioritaire pour ledéveloppement des satellites d’observation terrestre nouvelle génération.Il existe à l’heure actuelle deux principes fondamentaux de contrôle des micro-vibrations :• le contrôle dit passif: la stratégie consiste à introduire des dispositions constructives et des matériauxparticuliers permettant de minimiser la transmission des vibrations à l’environnement.• le contrôle dit actif : le concept de contrôle actif des vibrations est tout autre : l’idée est cette fois-ci,de bloquer la micro-vibration en exerçant une vibration antagoniste créée artificiellement avec despropriétés en opposition, à tout instant, relativement à la vibration indésirable, pour rendre nulleleur somme.L’industrie spatiale aborde cette problématique en plaçant des isolateurs en élastomère au voisinage dechaque source de micro-vibrations. Cette solution, qui a fait ses preuves puisqu’elle équipe actuelle-ment nombre de satellites en orbite, permet de rejeter nombre de micro-vibrations. Malheureusement,la demande de plus en plus importante de grande stabilité de la ligne de visée pour les futures missionsd’observation terrestres telles que les missions GAIA rend l’approche passive insuffisante.L’ESA et Airbus Defence and Space, ont donc collaborer conjointement avec l’équipe ARIA au travers decette thèse, dans des travaux de recherche dans le domaine du contrôle actif pour palier ces problèmes.L’objectif visé est de coupler les approches passives et actives afin de rejeter à la fois les micro-vibrations enhautes fréquences (approche passive existant) et en basses fréquences (approche active objet des travauxde la thèse)