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Conceptual design of the pointing and control subsystem of the space infrared telescope facility

The Space Infrared Telescope Facility mission provides exciting pointing and control challenges. This paper describes the pointing and control subsystem (PCS) designed to meet these challenges. Cost, mass, performance, and life-time drove the choice of the new solar orbit and the re-design of the telescope, spacecraft, and the pointing and control subsystem. The PCS performs a number of key functions for the observatory, including pointing to and holding inertial targets, tracking moving targets, performing prescribed motion patterns, maintaining pointing constraints and providing safe hold during failure. To attain the high precision demanded by the observatory, the PCS relies on a sub-arcsecond star tracker and a 0.001 arcsecond resolution inertial reference unit. An affordable PCS is realized by locating the fine guidance sensor externally, utilizing a simple fault protection strategy, and maximizing the commonality in the use of hardware and in the development of flight software.