4.6 Flight Calibration/Maintenance

Calibration on celestial sources is necessary because the XRCF cannot effectively simulate a point-source at infinity. The XRCF results must be interpreted through a model accounting for the decreased effective area and other effects of a finite source distance.

A subset of the ground tests will serve to link them to the pre-flight status of the instrument. The celestial tests will also determine the stability of ACIS through launch, and provide a baseline for trend analysis, anticipating possible degradation of CCDs due to particle radiation or contamination. There will be a multi-energy calibration X-ray source on board used to monitor CTE change and check the level of the chip surface contamination, which can affect the low-energy response.