Managing radiation degradation of CCDs on the Chandra X-ray Observatory III

The CCDs on the Chandra X-ray Observatory are vulnerable to radiation damage,from low-energy protons scattered off the telescope's mirrors onto the focal plane. Following unexpected damage incurred early in the mission, the Chandra team developed, implemented, and maintains a radiation-protection program. This program—involving scheduled radiation safing during radiation-belt passes, intervention based upon real-time space-weather conditions and radiation- environment modeling, and on-board radiation monitoring with autonomous radiation safing—has successfully managed the radiation damage to the CCDs. Since implementing the program, the charge-transfer inefficiency (CTI) has increased at an average annual rate of only 3.2×10,(6.7%) for the back-illuminated CCDs. This paper describes the current status of the Chandra radiation-management program, emphasizing,enhancements,implemented,since the original paper. Keywords: X-ray astronomy, CCDs, radiation damage, radiation environment, spacecraft operations