ESA GNC Conference Papers Repository

Recent evolutions in the regulations bring more stringent requirements to the satellite end of life operations. Such requirements as passivation were not initially foreseen in the current on-orbit architectures whereas the fluidic passivation of the tanks generally lead to unusual thrusters behaviour. This study focuses on the management of the under-efficiency of the thrusters during this end of life operation. Thanks to an identification and filtering method, the objective is to monitor the balance of the system and to secure the passivation phase. Some end-of-life feared events are, not exhaustively, temporary gas bubbles, permanent drop of thrust or complete loss of force. Associated torque variations could be largely out of the range of the attitude controllers and, without ground intervention, lead to the loss of the satellite due to overrate, permanent unavailability of TM/TC link or drop of electrical power. The proposed method consists in monitoring the thrusters efficiency from the ground, using the information available in the telemetry. This allows detecting an anomaly on the propulsion subsystem, identification of the faulty thruster as well as evaluation of the under performance. The implementation is not dependent of the satellite architecture, as long as the thrusters commanded pulses are available in the telemetry and the rotation rate remains steady. The identification and filtering algorithm has been tested on simulation tool with various thrusters configurations and for different missions (Telecom, LEO satellites). It proved to accurately evaluate the thrusters efficiencies, although several forces were out of the nominal range. As an experience, the real telemetries from the telecommunication satellite Telecom-2C have been processed. Although some parts of the telemetry were missing, failures have been identified on the expected thrusters. The failure scenario has been cross-checked using temperature data from the thermal probes and pressure data. In addition, this monitoring will be applied for the passivation of the microsatellite Demeter in December 2010.