Alexandre Falcoz

Robust Fault Diagnosis for Atmospheric Reentry Vehicles: A Case Study

This paper deals with the design of robust model-based fault detection and isolation (FDI) systems for atmospheric reentry vehicles. This work draws expertise from actions undertaken within a project at the European level, which develops a collaborative effort between the University of Bordeaux, the European Space Agency, and European Aeronautic Defence and Space Company Astrium on innovative and robust strategies for reusable launch vehicles (RLVs) autonomy. Using an H∞/H- setting, a robust residual-based scheme is developed to diagnose faults on the vehicle wing-flap actuators. This 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 sufficient condition for robustness and FDI fault sensitivity over the whole vehicle flight trajectory. A key feature of the proposed approach is that the coupling between the in-plane and out-of-plane vehicle motions, as well as the effects that faults could have on the guidance, navigation, and control performances, are explicitly taken into account within the design procedure. The faulty situations are selected by a prior trimmability analysis to determine those for which the remaining healthy control effectors are able to maintain the vehicle around its center of gravity. Finally, some performance indicators including detection time, required onboard computational effort, and CPU time consumption are assessed and discussed. Simulation results are based on a nonlinear benchmark of the HL-20 vehicle under realistic operational conditions during the autolanding phase. The Monte Carlo results are quite encouraging, illustrating clearly the effectiveness of the proposed technique and suggesting that this solution could be considered as a viable candidate for future RLV programs.

Periodic FIR controller synthesis for discrete-time uncertain linear systems

This paper is concerned with robust state-feedback controller synthesis for discrete-time linear periodic/time-invariant systems subject to polytopic-type parametric uncertainties. In recent studies, some of the authors conceived an LMI-based approach to periodically time-varying memory controller (PTVMC) synthesis and proved that this approach is indeed effective to get less conservative robust controller design procedures. However, since the peculiar controller structure requires to reset memory to zero in a periodic way, it is pointed out that the control performance depends on the timing of implementation. In this paper we tackle this issue and propose a reset-less state-feedback Periodic FIR Controller (PFIRC), which turns out to be suitable to improve robustness on periodic and time-invariant systems. Moreover, as a special case, a design condition is provided for FIR-type LTI controllers that robustly stabilize uncertain LTI systems. Numerical examples illustrate the efficiency of the proposed approaches.

Periodic H 2 synthesis for spacecraft attitude control with magnetorquers and reaction wheels

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.

Robust Stability of Periodic Systems with Memory: New Formulations, Analysis and Design Results

Abstract In this paper, the general formulation of periodically time-varying state-feedback controllers with memory is considered for the first time. New analysis and synthesis conditions for robust stability are proposed. The flexibility of these new results allows the user to freely add degrees-of-freedom to the control law which appears to effectively reduce the conservatism of the synthesis condition and to increase the stability domain of the closed-loop system in the presence of uncertainties. Furthermore, it is shown that for a particular structure of controllers a more efficient version of the design theorem can be derived by enriching the matrix of slack-variables.

Robust Fault Diagnosis strategies for Spacecraft Application to LISA Pathfinder experiment

Abstract This paper presents research activities conjointly led by EADS Astrium Satellites and the European Space Agency on innovative and robust health monitoring system for the next generation of spacecraft. Two robust FDI schemes are presented to detect and isolate faults affecting the micro-Newton colloidal thrust system of the LISA Pathfinder spacecraft. The first FDI strategy is based on a bank of eight H ∞ / H − residual generators designed according to the Generalized Observer Strategy whereas the second strategy consists of Kalman-based projected observers. The efficiency of the proposed FDI techniques is assessed through non linear simulations performed under realistic conditions (physical parameter uncertainties, disturbances, measurement noises, measurement delays, thruster jet misalignment,…). The results are quite encouraging, illustrate the effectiveness of the proposed techniques and suggest that the solutions could be practical viable candidates.

Microvibration Attenuation based on H∞/LPV Theory for High Stability Space Missions

This paper presents a LPV (Linear Parameter Varying) solution for a mixed passive-active architecture used to mitigate the microvibrations generated by reaction wheels in satellites. In particular, H∞/LPV theory is used to mitigate low frequency disturbances, current baseline for high frequency microvibration mitigation being based on elastomer materials. The issue of multiple harmonic microvibrations is also investigated. Simulation results from a test benchmark provided by Airbus Defence and Space demonstrate the potential of the proposed method.

Integrated Structure/Control Optimisation Applied to the BIOMASS Earth Observation Mission

A new approach of an integrated structure/control co-design methodology is developed based on the recognition that a high degree of coupling exists between the control and structural disciplines in the control of flexible space structures. A unified computational framework is developed gathering methodologies and tools coming from robust control theory and advanced worst case analysis techniques together with mechanical modelling engineering tools. Within this environment, design iterations consist in updating critical control and structure design variables by assessing controlled performance while minimizing structural mass. The optimisation process utilises a Differential Evolution algorithm. Multiobjective optimisation is also supported highlighting the compromise between mechanical and control objectives. The Linear Fractional Transformation formalism provides an uncertain representation of the spacecraft dynamics which is considered during the controller synthesis and analysis processes together, managed in the H∞/μ setting. Traditional Monte-Carlo simulations evaluate the robust performance of the controller design whilst optimisation-based worst-case analysis has been implemented to increase the efficiency of the worst-case extraction. This paper presents the work supported by the European Space Agency in the scope of the robust AOCS technology program initiated to support the BIOMASS mission; a candidate for the Earth Explorer Core 7 missions.

Integrated Control and Structure design framework for spacecraft applied to Biomass satellite.

Abstract This paper presents a research activity on the design of an Integrated Control Structure framework enabling to ensure co-jointly structure sizing and robust control design for flexible satellite. This work has been supported by the European Space Agency in the scope of the robust AOCS technology program initiated to support Biomass phase A mission. An Integrated Modeling, Control and Analysis Framework (IMCA) has been developed and exploited to optimize the articulated arm of Biomass satellite reflector while guaranteeing the existence of a controller fulfilling mission requirements. AOCS and Mechanical engineering tools have been merged into a single and unified multilevel optimization process where a spacecraft structure parameter set is iteratively and automatically updated to minimize the overall structure mass. The control design problem has been formulated and managed in the H ∞ /μ setting and the optimization process executed using Differential Evolution algorithm.

Robust ℌ ∞ performance of periodic systems with memory: New formulations, analysis and design results

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.