Attitude control laws that use control moment gyros (CMGs) and momentum wheels are derived with nonlinear techniques. The control laws command the CMGs to provide rapid angular acceleration and the momentum wheels to reject tracking and initial condition errors. Numerical simulations of derived control laws are compared. A trend analysis is performed to examine the benefits of the derived controllers. We describe the design of a CMG built using commercial off-the-shelf (COTS) equipment. A mixed attitude control strategy is implemented on the spacecraft simulator at Virginia Tech. / Master of Science

Dans cette thèse, le problème du contrôle d’attitude de satellites agiles à l’aide de grappes d’actionneurs gyroscopiques (AGs) est considéré et plus particulièrement son application au contrôle de micro/nanosatellites (10-100 kg). Des outils d’analyse topologique sont tout d'abord développés. La comparaison de différentes configurations de grappes justifie le choix d'une géométrie pyramidale à six actionneurs gyroscopiques. Des analyses plus approfondies de cette grappe, avec et sans cas de panne, permettent de déduire des contraintes que la loi de pilotage doit vérifier pour être adaptée à ce système. Pour y répondre, après analyse de la littérature, une nouvelle structure de loi de pilotage ainsi qu’une formulation différente des équations cinématiques sont développées. Cette structure est basée sur l’algorithme du filtre de Kalman étendu. Elle a pour avantages de répondre aux exigences en termes de calcul temps réel au bord des satellites, de flexibilité sur la gestion des contraintes et de facilité d’adaptation en cas de pannes. En outre, une procédure de génération de boucle de commande, englobant la loi de pilotage et un contrôleur robuste du système, est proposée. La généralisation de cette boucle de commande est illustrée sur des bras manipulateurs à base fixe et spatiaux.En parallèle, l’étude du passage des singularités internes intraversables mène à une nouvelle stratégie d’évitement de ces singularités. Des simulations sur des modèles de satellites représentatifs illustrent les résultats. La grappe d’actionneurs et la boucle de commande développées seront testées dans le cadre d’une expérimentation en microgravité. / In this thesis, the attitude control problem for agile satellites with control moment gyro (CMG) clusters is studied. In particular, the problem applies to micro/nanosatellites (10-100kg). First, numerical tools are developed to analyse the compatibility of various cluster configurations with the nanosatellite constraints. The pyramidal six-CMG cluster is then selected. This cluster topology is analysed in depth, with and without actuator failures. Constraints on the development of a steering law adapted to our system are deduced. Among them, the singularity avoidance issue is emphasised. To meet the requirements, an analysis of the literature is carried out. Then, a new steering law structure and a different formulation of the kinematic equations are developed. This structure is based on the extended Kalman filter algorithm. It meets the requirements because it can be calculated in real-time onboard satellites, constraints imposed on the system are handled with flexibility and it is easily adaptable in case of actuator failures. In addition, a procedure to generate the control loop is proposed, containing a robust controller. The generalisation of this control loop is shown on space and fixed-base manipulator arms. Furthermore, the study of the internal elliptic singularities in CMG clusters leads to a new singularity avoidance strategy. Software simulations on highly representative simulators show the results of the steering law in various actuator failure cases. The CMG cluster and the control loop will be tested in a parabolic flight campaign, and the development of this experiment is detailed in this thesis.

This thesis addresses the attitude control of satellites with similar and dissimilar actuators and control allocation methods on maneuvering. In addition, the control moment gyro (CMG) steering with gyroscopes having limited gimbal angle travel is also addressed. Full Momentum envelopes for a cluster of four CMG&#039 / s are obtained in a pyramid type mounting arrangement. The envelopes when gimbal travel is limited to plus-minus 90 degree are also obtained. The steering simulations using Moore Penrose (MP) pseudo inverse as well as blended inverse are presented and success of the pre planned blended inverse steering in avoiding gimbal angle limits is demonstrated through satellite slew maneuver simulations, showing the completion of the maneuver without violating gimbal angle travel restrictions. Dissimilar actuators, CMG and magnetic torquers are used as an approach of overactuated system. Steering simulations are carried out using different steering laws for constant torque and desired satellite slew maneuver scenarios. Success of the blended inverse steering algorithm over MP pseudo inverse is also demonstrated

A Variable Speed Control Moment Gyro (VSCMG) is a recently introduced actuator for spacecraft attitude control. As its name implies, a VSCMG is essentially a single-gimbal control moment gyro (CMG) with a flywheel allowed to have variable spin speed. Thanks to its extra degrees of freedom, a VSCMGs cluster can be used to achieve additional objectives, such as power tracking and/or singularity avoidance, as well as attitude control. In this thesis, control laws for an integrated power/attitude control system (IPACS) for a satellite using VSCMGs are introduced. The power tracking objective is achieved by storing or releasing the kinetic energy in the wheels. The proposed control algorithms perform both the attitude and power tracking goals simultaneously. This thesis also provides a singularity analysis and avoidance method using CMGs/VSCMGs. This issue is studied for both the cases of attitude tracking with and without a power tracking requirement. A null motion method to avoid singularities is presented, and a criterion is developed to determine the momentum region over which this method will successfully avoid singularities. The spacecraft angular velocity and attitude control problem using a single VSCMG is also addressed. A body-fixed axis is chosen to be perpendicular to the gimbal axis, and it is controlled to aim at an arbitrarily given inertial direction, while the spacecraft angular velocity is stabilized. Finally, an adaptive control algorithm for the spacecraft attitude tracking in case when the actuator parameters, for instance the spin axis directions, are uncertain is developed. The equations of motion in this case are fully nonlinear and represent a Multi-Input-Multi-Output (MIMO) system. The smooth projection algorithm is applied to keep the parameter estimates inside a singularity-free region. The design procedure can also be easily applied to general MIMO dynamical systems.