a b s t r a c tThis paper deals with the design and validation of an active fault-tolerant control system to detect, isolate and accommodate a single thruster fault affecting the thruster-based propulsion system of an autonomous spacecraft. The proposed method consists of a fault detector for robust and quick fault detection, a two-stage hierarchical isolation strategy for fault isolation, and an online control allocation unit scheduled by the isolation scheme for fault tolerance. A new factorization approach for the uncertain inertia matrix inverse is proposed. Thanks to this factorization, a novel robust Nonlinear Unknown Input Observers (NUIO) approach is proposed based on LMIs which ensure maximization of the admissible Lipschitz constant while at the same time satisfying an L 2 gain bound and some constraints on the observer dynamics. At the first stage of the isolation scheme, a bank of NUIOs is used to identify a subset of possible faulty thrusters. Then, at the second stage, an EKF is introduced to estimate the torque bias directions. Using these directions, jointly with the detector's residual and the information obtained from the first stage, a set of explicit rules is derived to unambiguously isolate the faulty thruster. A Monte Carlo campaign, based on a simulator developed by Thales Alenia Space industries, is conducted in the context of a terminal rendezvous phase of the Mars Sample Return mission. Mission oriented criteria demonstrate that the proposed strategy is able to cope with a large class of realistic thruster faults and to achieve mission success.
International audienceThe aim of this paper is to consider the modelling and control issues arising in the design of a station keeping system for geostationary satellites based on electric propulsion. In particular, a linear time-varying model for the dynamics of a geostationary satellite affected by perturbations is derived and the longitude and latitude station keeping problem is then formulated as a constrained linear quadratic optimal control problem. A direct method based on the so-called differential inclusion approach is then proposed. Simulation results showing the feasibility of the control task on a spacecraft equipped with electric thrusters are also presented and discussed
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