Improving the safe mode robustness of an Earth observation satellite

Sammanfattning: Airbus Defence and Space is developing an Earth observation platform. The payload of that platform is an optical instrument, which has to be protected from Sun dazzling in order to preserve its integrity. This is most difficult for the safe mode of a satellite, an operating mode during which all non-essential systems are shut down, including parts of the attitude control and estimation. A safe mode in low Earth orbit usually relies on the Earth magnetic field to stabilize a tumbling motion and eventually find the Sun. As such it avoids making use of complex and powerhungry actuators such as star trackers or gyroscopes, which makes for particularly robust safe modes. However, this limited use of equipment may prevent the satellite from relying on a Sun avoidance to protect the instrument, as usually done by the ground control teams. In this context, the approach to a dazzling risk evaluation in safe mode is presented in this thesis. This study was performed using the Monte Carlo method, with repeated random sampling on a simulator to estimate the probability of a payload dazzling occurrence. An alternative tuning of the safe mode, optimized for dazzling risk reduction is also studied, as well as new control law that makes use of gyroscopes to render close to statistically impossible the occurrence of any payload dazzling.