Disposal Operation Strategies for Remote Sensing Satellite Fleets In Nominal and Emergency Situations

Since December 2010, a new French Law on Space Operations (LSO) must be complied with by any entity related to space activities. It imposes, for instance, that any satellite operator shall demonstrate his capability to control the space vehicle, whatever the mission phase from the launch up to its End Of Life (EOL). The French Space Agency (CNES) is currently operating several remote sensing satellites (the last one called PLEIADES 1A), among a larger fleet of satellites. In that context, CNES has decided to perform several specific studies in order to define satellite disposal operation plans in any situation. The typical scenario of EOL operations consists in implementing five phases : disposal orbital manoeuvres, fluidic passivation, electrical passivation, transmitter disconnection and EOL orbit computation. One shall point out that these satellites (except PLEIADES 1A and 1B) were not originally designed to conform with the constraints imposed by the LSO. Thus, detailed analysis were conducted to identify the on-board and the on-ground improvements, as well as the operations chronology, without compromising in any way the security in the conduct of the operations. Depending on the context (nominal, contingency or emergency case) and the satellite subsystems status, different scenarios have been defined and compared in terms of strategy of disposal orbital manoeuvres, on-board and on-ground software upgrades, cumbersome operations, complexity, feedback... This paper addresses this tradeoff, and moreover, it focuses on two main points : 1) the on-board software upgrades (monitoring parameters, Failure Detection Isolation Recovery strategy, chronology and constraints of modifications upload) and the equipment that must be switched off or for which configuration parameters must be tuned, 2) the different disposal orbit manoeuvre strategies : several Orbit Control Manoeuvres (OCM), one or two OCMs followed by an infinite-duration thrust, or an unique infinite-duration thrust. In conclusion, the generic principles applied in these studies could be considered as guidelines for any other satellite platform EOL operations.