Overview of PLATO’s cameras on-ground and in-orbit calibration and characterisation

Abstract

The PLAnetary Transits and Oscillations of stars mission (PLATO) is the M3 mission in ESA’s Cosmic Vision 2015-2025 Programme. The PLATO mission aims at detecting and characterizing extrasolar planetary systems, including terrestrial exoplanets around bright solar-type stars in the habitable zone. In order to achieve its scientific objectives, PLATO must perform uninterrupted high precision photometric monitoring of large samples of stars during long periods to detect and characterize planetary transits. The PLATO light curves will also contain information on the seismic activity of the stars, which will lead to the determination of radii and ages of parent stars. The scientific payload of PLATO, developed and provided by the PLATO Mission Consortium (PMC), is based on a multi-telescope configuration consisting of 24 “Normal” (N) cameras and 2 “Fast” (F) cameras, so as to provide simultaneously a large field of view and a large collecting aperture. The optical design is identical for all cameras and consists of a 6-lens dioptric design with a 120 mm entrance pupil and an effective field of view of more than 1000 deg2. The calibration and characterization of PLATO’s cameras is a real challenge, especially in terms of quantities: there are 24 FMs + 2 Flight Spares + 2 Qualification Models and finally 1 EM to calibrate. In this context, the on-ground calibration and characterization plan of the cameras was developed to the strict minimum needed. This means that all the measurements that can be performed in-orbit will not be calibrated on-ground. Our aim is to give an overview of the on-ground activities planned in the coming years to calibrate, characterize and verify the PLATO’s cameras, both in terms of organization and technical solutions. In particular, a detailed description of the geometric calibration used for the Fine Guidance System (FGS) and the focusing calibration will be given. PLATO’s Cameras have indeed the unusual but powerful feature to use a temperature control system to refine their focus. A description of the in-flight calibration plan (including for example the repetition of the focusing calibration, the micro-scanning procedure to determine high-resolution PSFs) will then be given to get the full overview of the calibration, characterization and verification of PLATO’s cameras. Calibrating and verify so many cameras in space, without any calibration targets/sources on board, only using pointing capabilities of the satellite, stellar targets and advanced data processing is a real challenge for this mission. A particular attention will be given to the micro-scanning procedure and inversion techniques required for precise PSF Modelling.