On board processing procedures for the Solar Orbiter METIS coronagraph

Solar Orbiter is an ESA space mission devoted to improve the knowledge of those effects nowadays still not fully understood on the physical mechanisms underlying the behaviour of our star. The mission has a peculiar trajectory that will bring the S/C close to the Sun up to 0.28 AU, exploiting the opportunity to follow up our star as close as never before. METIS, one of the instruments selected to be part of the Solar Orbiter payload, is a coronagraph that will investigate the inner part of the heliosphere performing imaging in the visible band and in the hydrogen Lyman α line @ 121.6 nm. METIS will be able to simultaneously operate the two detectors: an Intensified APS for the UV channel and an APS for the visible light, and a Liquid Crystal Variable Retarder (LCVR) plate, for broadband visible polarimetry. They will be operated by means of the centralised management unit of the instrument, the METIS Processing and Power Unit. This payload subsystem hosts a microprocessor that implements, thanks to the application software, all the needed functionalities to fully control the instrument subsystems and its own processing capabilities. Both sensors will be readout at high rate and the acquired data shall undergo through a preliminary on-board processing to maximize the scientific return and to provide the necessary information to validate the results on ground. Being Solar Orbiter a deepspace mission, some METIS procedures have been designed to provide to the instrument an efficient autonomous behaviour in case of an immediate reaction is required as for arising transient events or occurrence of safety hazards condition. METIS will implement an on-board algorithm for the automatic detection of this kind of events in order to promptly react and autonomously adapt the observing procedure.