The effect of ice build-up on the soft X-ray response of a charge coupled device (CCD)

The potential for spacecraft contaminants to outgas in orbit and condense onto the cold surfaces of X-ray CCDs has been appreciated for some time. We investigate the effect of ice build-up on the low-energy response of a soft X-ray sensitive CCD. We derive curves relating the build up of ice with the partial pressure of water vapour and CCD temperature. Ice build-up predictions and ice removal strategies, based on these curves, are determined for the CCDs to be flown on the JET-X telescope. A discussion of anti-icing measures is given.