Orbital Operations with the Shuttle Infrared Telescope Facility (SIRTF)

The Shuttle Infrared Telescope Facility (SIRTF) is a cryogenically-cooled, 1-m-class telescope that will be operated from the Space Shuttle as an observatory for infrared astronomy. Over the 2- to 200-μm band, SIRTF will be 100 to 1000 times more sensitive than existing infrared facilities. This paper discusses the scientific constraints on and the requirements for pointing and controlling SIRTF as well as several aspects of SIRTF orbital operations. The basic pointing requirement is for an rms stability of 0.25 arcsec, which is necessary to realize the full angular resolution of the 5-μm diffraction-limited SIRTF. Achieving this stability requires the use of hardware and software integral to SIRTF working interactively with the gyrostabilized Shuttle pointing-mount. The higher sensitivity of SIRTF, together with orbital and time constraints, puts a premium on rapid target acquisition and on efficient operational and observational procedures. Several possible acquisition modes are discussed, and the importance of source acquisition by maximizing the output of an infrared detector is emphasized. The ability of the pointing-mount to slew the telescope over a range of angles is discussed, including its capability for executing raster scans over limited areas. Both minimum-time scans and constant-rate scans, which may take significantly longer in some cases, are discussed.