The Chandra X-Ray Observatory's Radiation Environment and the AP-8/AE-8 Model

摘要

The Chandra X-ray Observatory (CXO) was launched on July 23, 1999 and reached its final orbit on August 7, 1999. The CXO is in a highly elliptical orbit, approxiamtely 140,000 km x 10,000 km, and has a period of approxiamtely 63.5 hours (approx approx 2.65days). It transits the Earth's Van Allen belts once per obit during which no science observations can be performed due to the high radiation environmetn. The Chandra X-ray Observatory Center (CXC) currently uses the National Space Science Data Center's "near Earth" AP-8/AE-8 radiation belt model to predict the start and end times of passage through the radiation belts. However, oru scheduling software uses only a simple dipole model of the Eart's magnetic field. The resuting B,L magnetic coordiantes, do not always give sufficiently accurate predictions of the start and end tiems of transit of the Van Allen belts. We shwo this by comparing to the data from Chandra's on-board radiation monitor, the EPHIN (Electron, Proton, helium Instrument particle detector) instrument. We present evidence tha demonstrates this mis-timing of the otuer electron radiation belt as well as data that also demosntrate hte significnat variability of one radiation belt transit to the next as experienced by the CXO. We also present an explanation for why the dipole implementation of hte AP-8/AE-8 model is not ideally suited for the CXO. Lastly, we provide a brief discussion of our on-going efforts to identify a model that accounts for radiation belt variability, geoemtry, and one that can be used for observatio nscheduling purposes.