11 March 2003 Managing radiation degradation of CCDs on the Chandra X-ray Observatory
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Abstract
The CCDs on the Chandra X-ray Observatory are sensitive to radiation damage, particularly from low-energy protons scattering off the telescope's mirrors onto the focal plane. In its highly elliptical orbit, Chandra passes through a spatially and temporally varying radiation environment, ranging from the radiation belts to the solar wind. Translating the Advanced CCD Imaging Spectrometer (ACIS) out of the focal position during radiation-belt passages has prevented loss of scientific utility. However, carefully managing the radiation damage during the remainder of the orbit, without unnecessarily sacrificing observing time, is essential to optimizing the scientific value of this exceptional observatory throughout its planned 10-year mission. In working toward this optimization, the Chandra team developed and applied a radiation-management strategy. This strategy includes autonomous instrument safing triggered by the on-board radiation monitor, as well as monitoring, alerts, and intervention based upon real-time space environment data from NOAA and NASA spacecraft. Furthermore, because Chandra often spends much of its orbit out of the solar wind (in the Earth's outer magnetosphere and magnetosheath), the team developed the Chandra Radiation Model to describe the complete low-energy-proton environment. Management of the radiation damage has thus far succeeded in limiting degradation of the charge-transfer inefficiency (CTI) to less than 3.5(10-6) and 1.3(10-6) per year for the front-illuminated and back-illuminated CCDs, respectively. This rate of degradation is acceptable for maintaining the scientific viability of all ACIS CCDs for more than ten years.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Stephen L. O'Dell, Stephen L. O'Dell, William C. Blackwell, William C. Blackwell, Robert A. Cameron, Robert A. Cameron, Joseph I. Minow, Joseph I. Minow, David C. Morris, David C. Morris, Bradley J. Spitbart, Bradley J. Spitbart, Douglas A. Swartz, Douglas A. Swartz, Shanil N. Virani, Shanil N. Virani, Scott J. Wolk, Scott J. Wolk, "Managing radiation degradation of CCDs on the Chandra X-ray Observatory", Proc. SPIE 4851, X-Ray and Gamma-Ray Telescopes and Instruments for Astronomy, (11 March 2003); doi: 10.1117/12.461493; https://doi.org/10.1117/12.461493
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