Performance of the Advanced Camera for Surveys CCDs after two years on orbit

The Advanced Camera for Surveys (ACS), installed in the Hubble Space Telescope (HST) in March 2002, comprises three cameras: the Wide Field Camera (WFC), designed for deep near-IR survey imaging programs; the High Resolution Camera (HRC), a high angular resolution imager which fully samples the HST full spread function (PSF) in the visible; and the Solar Blind Camera (SBC), a far-UV imager. The WFC and HRC employ CCD detectors. Their performances are affected by the on-going damage due to the space radiation environment where they operate. We present an overview of the performance of the ACS CCD detectors, based on the first two years of flight science operations. We analyze the evolution with time of the basic detector performance that are subjected to degradation due to the on-going radiation damage. Comparison is made with ground testing prediction and with the amount of performance degradation seen in other CCD detectors on board of HST.