ADVANCED X-RAY ASTROPHYSICS FACILITY-SPECTROMETRY SPACECRAFT POINTINGCONTROL-SYSTEM - CONCEPTUAL DESIGN

The Advanced X-Ray Astrophysics Facility-Spectrometry is an orbiting a stronomical observatory using grazing-incidence optics to focus x-ray images on a liquid-helium-cooled imaging x-ray spectrometer (XRS). It will be launched on a Delta-II launch vehicle into a 650-km, circular, sun-synchronous orbit and will be operated as a national observatory for an expected period of 5 years. This paper describes the conceptual design of the pointing control system (PCS), whose function is to acq uire x-ray targets on the XRS detector and maintain a pointing stabili ty of 5.5 '' (rms) per axis over any 10-min period that excludes a day -night or night-day terminator crossing. The proposed PCS design attem pts to use the best features of previous PCS designs, but has several new features not found on other spacecraft. Hence, it can serve as a g ood starting point and reference for PCS designers of future spacecraf t. Error budgets and preliminary simulation results show the soundness of tile design approach.