PLATO flight model cameras TVAC focus calibration

Kurzfassung

The PLAnetary Transits and Oscillations of stars (PLATO) mission aims at detecting and characterizing extrasolar planetary systems, including terrestrial exoplanets orbiting up to the habitable zone around bright solar-type stars1.2 The scientific payload of PLATO, developed and provided by the PLATO Mission Consortium (PMC) and ESA, is based on a multi-telescope configuration consisting of 24 Normal Cameras (N-CAM) and 2 Fast Cameras (F-CAM), so as to provide simultaneously a large field of view and a large collecting aperture. Each individual camera can be thermally re-focused in order to compensate for the accumulated integration errors between the Telescope Optical Unit (TOU) and the Focal Plane Assembly (FPA). It allows to operate each camera in-orbit at its optimum setpoint, minimizing the average PSF size of the stars on the focal plane. To achieve this, the camera itself is cold-biased on the spacecraft and its temperature is controlled by a Thermal Control System (TCS) that allows to reach a commanded stable temperature within the range [-90°C ; -70°C]. This work presents the preparation and results of the on-ground pre-launch calibration campaign of the cameras Flight Models (FM), scanning the complete temperature range and searching for the best focus temperature. A set of statistical data is presented, based on the assembly and testing of the first flight model cameras, confirming their high-quality and validating the processes defined for the serial production.