Christine E. Ritchie

Effects of the space environment on the HST Wide Field Planetary Camera-I

The wide field planetary camera was launched onboard the Hubble Space Telescope in April 1990 and returned to earth during the HST first servicing mission in December 1993. We report on the ongoing examination of the returned hardware. In particular, a significant decline in performance at UV wavelengths in the exterior optics has been found and studied. This appears to be the result of polymerization of molecular contamination on the external optics by UV light reflected off the Earths atmosphere. Some conlusions from a partial disassembly of the instrument and an examination of its filter elements are presented. We also discuss the effects of radiation on the CCD detectors during their stay in orbit. Radiation damage increased the numbers of hot pixels over time but had no other discernible effects on the performance of the CCDs.

On-orbit management of contaminants within the HST widefield planetary camera and their effect on instrument performance

The Wide Field Planetary Camera (WF/PC) onboard the Hubble Space Telescope contains contaminants which condense on the windows in front of each CCD detector. These contaminants are UV opaque and increase with time to the extent that after several months they block 50% of the flux at 300 nm. Also, when the contaminants are warmed above -40 degree(s)C and then returned to the normal CCD operating temperature of -87 degree(s)C, particles form and severely degrade the image quality. The windows may be temporarily cleaned by raising their temperature to 0 degree(s)C. However, this results in a change in the structure of the flat field due to the partial removal of the UV flood which was applied after launch to suppress Quantum Efficiency Hysteresis in the CCDs. Repeated decontaminations will reintroduce the QEH and necessitate another time consuming UV flood and recalibration of the instrument. After 22 months of on-orbit operation, the contaminants could no longer be fully removed by the decontamination procedure. This paper describes the current state of the contaminants, what has been deduced concerning their properties and sources, the results of our efforts to remove them, and some lessons for future space-based instruments using cryogenic UV sensitive detectors.