PLATO focal plane assembly (FPA) qualification model (QM): an innovative real-time metrology

The PLAnetary Transits and Oscillations of stars mission (PLATO) is an ESA M3 mission planned to detecting and characterizing extrasolar planetary systems as Earth-like exoplanets orbiting around the habitable zone of bright solartype stars. PLATO consists of 26 cameras (CAM) mounted on the same instrument platform in order to cover a large field of view (FoV) with the highest possible photon detection statistics. Each PLATO CAM consists of a telescope Optical Unit (TOU), the FPA, and the detector read-out Front End Electronics (FEE). The FPA is the structure located at the focal plane position of the CAM that supports four identical CCDs and the mechanical interface parts to match with the TOU and FEE. Due to the critical repeatability aspect of the mission, each FPAs must be identical with very stringent specifications which includes strict opto-mechanical positioning tolerances. Also the number of FPAs that have to be manufactured, integrated and tested at the same time requires a special space industrialization process and an optimized metrology verification due to the very restrictive design and schedule constraints. In order to solve this challenge a flight-representative QM has been developed in order to validate a manufacturing, assembly, integration and verification (AIV) on-ground processes. As well, an innovative metrology system has being developed for improving the alignment and verification under the tightly AIV requirements before, during and after a proper qualified campaign in a very demanding environment. INTA has adapted into an ISO6 cleanroom facility a high accuracy and vast performance non-contact CNC vision dimensional measuring system, and has developed a Ground Support Equipment (GSE) for a real-time alignment step in order to reach that requirements.