Study and definition of CNES Pleiades earth observation satellites end-of-life operations

The French Space Agency (CNES) is currently operating the two remote sensing Pleiades satellites. Launched respectively in 2011 and 2012, and designed for 5 years in orbit, their excellent behavior in flight may lead to their mission extension. Anyway, in the frame of the French Law on Space Operations (LSO), the End Of Life (EOL) operations have been considered from the beginning, in particular for nominal cases where the stable energy state of the satellite leave enough time to manage its fluidic and electrical passivation. The main challenge of the fluidic passivation rests in the possibility to guaranty the satellite controllability when facing intermittent ejection of mixed hydrazine and helium gas by the thrusters. This implies to carefully tune both the duration of each maneuver and the actuators configuration. In order to manage worst cases, non-routine specific combinations of satellite modes and equipment’s configuration shall be set up. Based on the Pleiades Attitude and Orbit Control Systems (AOCS) capability, the theoretical analysis of EOL fluidic passivation has been performed, both for Normal and Survival AOCS modes. The electrical passivation strategy has also been studied to ensure that the satellite is protected against the long-term batteries’ degradation and explosion risk. The operational implementation of each solution has then been assessed, to cope with wider system constraints such as TM/TC visibility, post-maneuvers orbit determination process or manning.