A New Procedure for Tuning an Allocator and Designing a Robust High-Level Control Law for Over-Actuated Systems

This paper presents a new integrated procedure to tune a control law for overactuated mechanical systems that may encounter singularities. First, the allocator that divides the commands among the actuators is tuned thanks to a genetic optimization algorithm, that computes the optimal values of its parameters. Then, the open-loop system including the allocator is identified and a robust closed-loop controller is computed with the structured H_\infty method. Indeed, near singularities, the system and the allocator may create errors to deviate from these points or create delays to reconfigure the actuators, hence there is a need to create a closed-loop controller robust to these characteristics and to parameter variations. This procedure is carried out on a planar redundant robotic manipulator example. Simulation

Propellant Sloshing Torque H ∞ -based Observer Design for Enhanced Attitude Control

International audienceIn this paper a control-oriented LPV model of the sloshing torque arising during attitude maneuvers, supported by Computational Fluid Dynamics results, is presented and used for attitude control design. The proposed strategy essentially relies on the design of a robust LPV-based disturbance torque observer with the help of the structured multi-model H ∞ synthesis framework. The estimated torque is then used to improve a satisfying attitude controller initially designed without sloshing. The stability of the parameter-varying closed-loop system is finally proved with parameter-dependent Lyapunov functions

Nonlinear dynamic inversion for redundant systems using the EKF formalism

This paper presents an allocator for over-actuated systems based on the Extended Kalman Filter (EKF). The main advantages of the proposed approach are the greater flexibility in handling the constraints and its real-time capabilities. Based on the literature, theoretic convergence results, which ensure the convergence towards the local optimal values looked for, are presented. Another formulation of the kinematic equations of redundant systems that meet some constraints is also proposed in order to go through and/or avoid singularities. The two formulations are combined and applied to an academic example (a planar redundant manipulator arm)

Modeling and stability of balloon-borne gondolas with coupled pendulum-torsion dynamics

The objective of this paper is to fill the gap in literature on an exhaustive coupled pendulum-torsion model for balloon-borne systems. The development of such a model is required to explain the unexpected oscillatory behavior recorded on the flight data of scientific balloon-borne missions and more particularly the performance degradation due to the coupling of pendulum and azimuth dynamics through the azimuth control loop, which is classically designed using a decoupled torsion model. First, a complete dynamic model of balloon-borne systems is derived. The proposed model is applied to the Faint Intergalactic-medium Redshifted Emission Balloon (FIREBall) experiment and validated by flight data. Then, the stability issue raising from the commonly neglected coupling assumption is investigated. Sufficient stability conditions are presented by using positivity properties. Based on the FIREBall model, it is finally shown how the azimuth control can destabilize the pendulum dynamics, and how the proposed model can be used during preliminary design phases to size a flight chain and the associated control system to prevent this instability

Satellite Attitude Control with a six-Control Moment Gyro Cluster tested under Microgravity Conditions

International audienceThe attitude control of a satellite equipped with a six-Control Moment Gyro (CMG) cluster is studied, taking into account CMG failure cases and constraints like actuator saturation and real-time aspects. The design of the steering law that allocates the required torques among the actuators is made complex by singularities (gimbal angles of the CMGs where no torque can be created along an axis). This paper describes the problem of a constrained allocation applied to the CMG system, and explains the selected solution. An experimental setup with six CMGs has been designed. It calculates in real-time the attitude guidance laws and control loop. Agile manoeuvres simulating nanosatellite attitude reorientations have been successfully carried out during a European Space Agency (ESA) parabolic flight campaign. The results show that the steering law performs as expected even in case of CMG failures

Satellite Attitude Control with a six-Control Moment Gyro Cluster tested under Microgravity Conditions

The attitude control of a satellite equipped with a six-Control Moment Gyro (CMG) cluster is studied, taking into account CMG failure cases and constraints like actuator saturation and real-time aspects. The design of the steering law that allocates the required torques among the actuators is made complex by singularities (gimbal angles of the CMGs where no torque can be created along an axis). This paper describes the problem of a constrained allocation applied to the CMG system, and explains the selected solution. An experimental setup with six CMGs has been designed. It calculates in real-time the attitude guidance laws and control loop. Agile manoeuvres simulating nanosatellite attitude reorientations have been successfully carried out during a European Space Agency (ESA) parabolic flight campaign. The results show that the steering law performs as expected even in case of CMG failures

Autonomous navigation system for free floating experiments in parabolic flights

This paper presents the development of an Extended Kalman Filter for the navigation system of a spacecraft in a parabolic flight. The algorithm blends the measurements coming from two Inertia Measurement Units, one mounted on the spacecraft and one on the baseplate of the aircraft; and a camera system connected to the baseplate as well. During the zero-g phases the attitude and position of the spacecraft in the experimental area are recovered thanks to a series of Alvar markers attached on the spacecraft casing and detected by the camera system. Results from parabolic test campaign of October 2019 are finally presented

Nouvelles configurations de grappes d’actionneurs gyroscopiques pour le contrôle de satellites agiles

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. After comparison of the configurations, the pyramidal six-CMG cluster is 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. The requirements initially defined in the thesis are therefore expanded. 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. It contains the steering law and a robust system 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 singularityavoidance strategy. It consists in adding the knowledge of the system topology in the steering law to enhance the precision of the maneuvers. 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.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). Afin d’analyser les configurations de grappe les plus pertinentes pour les nanosatellites, des outils d’analyse topologique sont développés. Après une comparaison des différentes configurations, le choix se porte sur une grappe pyramidale de six actionneurs gyroscopiques. Des analyses plus approfondies de cette grappe (avec et sans cas de panne d’actionneurs gyroscopiques) permettent de déduire des contraintes que la loi de pilotage doit vérifier pour être adaptée à ce système, en particulier pour le passage de singularités.Le cahier des charges initialement défini pour la thèse est alors étoffé et précisé. 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 dans les grappes d’actionneurs gyroscopiques mène à une nouvelle stratégie d’évitement de ces singularités. Elle consiste à insérer une connaissance de la topologie du système pour améliorer la précision dans le pilotage. Des simulations sur des modèles de satellites représentatifs illustrent les résultats de la loi de pilotage dans différents cas de panne. La grappe d’actionneurs et la boucle de commande développées seront testées dans le cadre d’une expérimentation en microgravité, et les objectifs de cette expérience sont détaillés dans ce mémoire

New configurations of control moment gyro clusters for the control of agile satellites

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