Gaia's FPA: sampling the sky in silicon

ESA´s astrometry satellite Gaia is scheduled for launch in 2013. In a combination of outstanding hardware performance, autonomous object detection and sophisticated data processing, Gaia will chart more than a billion stars of the entire sky to unprecedented accuracy during its 5 years mission. A key element to its mission success is the focal plane assembly (FPA), the largest ever flown to space, comprising a close-butted almost Giga-pixel mosaic of 106 large area CCDs. Manufacturing and extensive testing of the individual devices and detector system units as well as integration on the single-piece, silicon-carbide support structure has been a challenge. The focal plane is now assembled and has undergone its final tests during 2012. The paper summarizes the expected in-flight performances of Gaia´s FPA and the implemented tools and procedures to monitor its operation in space. Accurate knowledge of the impact of FPA performance parameters on individual measurements and its evolution in time is critical to achieve the high accuracy needed in calibrating the science data. An example is the radiation-induced deterioration of the CCD charge transfer efficiency, which acts on distorting the detected object PSFs while observing the sky in continuous scan mode. Through dedicated calibration procedures and directly through the scientific data processing, Gaia will therefore closely track the radiation environment at L2 from the FPA output itself. Detection of transient effects and analysis of persistent damage on the CCDs mainly caused by solar protons converts Gaia's FPA inherently into the largest ever radiation monitor in space.