Measuring radiation damage to the Hubble Space Telescope over 23 years and correcting it using ArCTIc

Since its launch, the Hubble Space Telescope’s Advanced Camera for Surveys (ACS) has been exposed to damaging radiation above the atmosphere. We track the degradation of the ACS’ image quality and find the rate of damage to be modulated by 18.5% during an 11-year solar cycle, peaking 430 days after (i.e. out of phase with) solar minimum based on the number of sunspots. We also find that the type of damage is consistent with defects in the silicon lattice that have all stabilised into one of three configurations. To correct for radiation damage in ACS images, we present the Algorithm for Charge Transfer Inefficiency correction (ArCTIc) v7. It models the physical processes that cause radiation damage to manifest in images. By calibrating ArCTIc using the trailing from ‘hot pixels’ and applying it to astronomical images, we correct 99.9 % of trailing in the worst-affected recent data and 99.5% of trailing averaged over the ACS’s lifetime.