Radiation damage to the Hubble Space Telescope during two Solar cycles, and correction of Charge Transfer Inefficiency using ArCTIc

Abstract

From 2002 to 2025, the Hubble Space Telescope's Advanced Camera for Surveys has suffered in the harsh radiation environment above the protection of the Earth's atmosphere. We track the degradation of its image quality, as Solar protons and galactic cosmic rays have damaged its photosensitive charge-coupled device (CCD) imaging sensors. The rate of damage in low Earth orbit is modulated by $18.5^{+4.5}_{-0.5}$ per cent during an 11 year Solar cycle, peaking $430^{+11}_{-5}$ days after Solar minimum as recorded in the number of sunspots. The type of damage is consistent with defects in the silicon lattice that have all stabilised into one of three configurations. We also present the open-source Algorithm for Charge Transfer Inefficiency correction (ArCTIc) v7. This models the (instantaneous or gradual) capture of photoelectrons into lattice defects, and their release after (a discrete set or continuum of) characteristic time delays, which creates spurious trailing in an image. Calibrated using the trailing of hot pixels, and applied during post-processing of astronomical images, ArCTIc can correct 99.5% of Charge Transfer Inefficiency trailing averaged over the camera's lifetime, and 99.9% of trailing in the worst-affected recent data.