Straylight analysis of the external baffle of COROT

The COROT mission is part of the program "mini-satellite" of CNES (French space agency). It implies international cooperation between European institutes and research centres. COROT aims to perform astroseismology observations and to detect exoplanets. Long duration observations of stars will be used to detect periodic variations with an afocal telescope followed by a dioptric objective and 4 CCDs. These very small variations can be caused by star seismic activities (about 10-6 variation of signal) or transits of planets (few 10-4 variation of signal). Due to the orbit of the spacecraft (low altitude polar orbit) and even if the observations are performed in a direction perpendicular to orbit plane, the measurements can be disturbed by the straylight reflected by the earth (albedo) that can generate a periodic perturbation. The paper details the overall optical design of the baffle. The baffle modelling and straylight computation methods are described and the expected performances are discussed. © 2017 SPIE.