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The ESA (European Space Agency) is currently pursuing the development of the e.Deorbit mission that will remove a large defunct satellite from Earth orbit: ENVISAT. To fulfil the mission autonomy requirements, ESA has decided to embed in the GNC (Guidance, Navigation, Control) software, fault tolerance capacities against actuator faults. The aim of this paper is to present the development and validation of a model-based fault diagnosis and tolerant control solution for such faults. The proposed solution is based on a new class of nonlinear unknown input observers, optimal in the L2-gain sense, and a modified version of the nonlinear inverse pseudo control allocation technique. An intensive simulation campaign conducted within a high-fidelity nonlinear industrial simulator, demonstrates the efficiency of the approach.

The design of a model-based Fault Tolerant Control (FTC) strategy based on Virtual Actuators (VA) in a built-in Guidance, Navigation and Control (GNC) setup is addressed for the e.Deorbit space mission. This mission, initiated by the European Space Agency (ESA), aims at removing a large defunct satellite from Earth orbit: ENVISAT. The goal of this paper is to promote academic solutions to add fault tolerance capacities against thruster faults without any change or new tuning of the already in-place GNC solution. The validation of the proposed FTC solution is assessed by a simulation campaign based on a high-fidelity nonlinear industrial simulator. § Corresponding author, 1 Authors are with the IMS-

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The goal of the activity On-ground Validation of Debris Removal Technologies, ORCO, has been to investigate and mature the complex couplings between the different control systems (GNC including image processing and robotics) for autonomous rigid capture between an active chaser vehicle and a cooperative/non-cooperative target, and derive the required algorithms and perform a HW-in-the-loop end-to-end demonstration. The prototyped solution is tested in the most realistic conditions obtainable on ground, including also the dynamics of the system as well as the relative visual based navigation system. The on-ground validation and integration is performed taking advantage of the GMV platform-art© dynamic test facility located in Madrid, Spain, with the addition of the hardware provided by the partners: robotic system from CBK (Poland) and visual system from TSD (Italy).