Twenty-Four Years of Radiation Protection of the Chandra X-Ray Observatory

This paper discusses the challenges and successes of radiation monitoring for the Chandra X-ray Observatory (Chandra). Now in operation for over 24 years, Chandra was originally designed with minimal concern for its space environment. However, just weeks into the mission, it was discovered that the charge-coupled devices on its primary detector were more vulnerable to radiation damage from low-energy (100-200 keV) protons than expected due to the ability of the Chandra mirrors to focus such protons. Its highly elliptical orbit, with a 63.5 h period, regularly takes the spacecraft through the Earth's radiation belts, the magnetosphere, the magnetosheath, and into the solar wind. Therefore, proper radiation management has been a prime concern of the Chandra team. A comprehensive approach utilizing scheduled radiation safing, in addition to onboard autonomous radiation monitoring, manual intervention, and specific orbital modeling, has proved successful at managing further radiation damage. Owing to the tremendous success and long duration of the mission, there have been a series of challenges in all of these approaches as the orbit has evolved and as the availability of both onboard and independent space-based monitoring has changed.