ESA GNC Conference Papers Repository

SENTINEL-2 is a European multi-spectral imaging mission using two identical satellites sharing one orbit. It is part of the Earth observation programme ?Copernicus? of the European Union. The first two satellites, Sentinel-2A and -2B, were launched in 2015 and 2017, respectively. A main challenge on board is to generate a precise satellite attitude knowledge. It is achieved by fusing measurements from two star trackers and a four-axis gyro unit. This paper attempts to determine the attitude estimation accuracy achieved in orbit without external attitude reference. Instead, the analysis is done via the innovation process in the estimation filter. For this, the innovation obtained with the performance simulator from the attitude and orbit control system development is compared to the innovation obtained with in-orbit measurements. On the way, the knowledge of inter star tracker alignment and relative star tracker / gyro unit alignment is analysed and improved. Finally, a fixed-interval smoother is developed allowing for the best attitude estimation accuracy in post-processing on ground w.r.t. estimation error variance.