KEYWORDS: Exoplanets, Software development, Control systems, Target recognition, Satellites, Space telescopes, Photometry, Stars, Space operations, Data processing
CHEOPS, the Characterizing Exoplanets Satellite, is a Swiss-led ESA-S mission carrying out ultra-high precision photometry providing radii of transiting exoplanets. We have developed the Instrument Flight Software, which controls the instrument and processes the science data in real-time. The software implements over 100 ECSS TM/TC services and several state machines, with data processing tasks ranging from target star recognition, centroiding, on-board data reduction and compression to thermal control and FDIR. The flight hardware is based on the dual-core Leon3 processor. We present the approach that we took towards specification, design, implementation and qualification, then talk about the lessons learned especially during the commissioning.
The CHaracterising ExOPlanet Satellite (CHEOPS) is the first ESA S-class and exoplanetary follow-up mission headed for launch in 2018. It will perform ultra-high-precision photometry of stars hosting confirmed exoplanets on a 3-axis stabilised sun-synchronous orbit that is optimised for uninterrupted observations at minimum stray light and thermal variations. Nevertheless, due to the satellites structural design, the alignment of the star trackers and the payload instrument telescope is affected by thermo-elastic deformations. This causes a high pointing uncertainty, which requires the payload instrument to provide an additional acquisition system for distinct target identification. Therefor a star extraction software and two star identification algorithms, originally designed for star trackers, were adapted and optimised for the special case of CHEOPS. In order to evaluate these algorithms reliability, thousands of random star configurations were analysed in Monte-Carlo simulations. We present the implemented identification methods and their performance as well as recommended parameters that guarantee a successful identification under all conditions.
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