Pre-launch performance testing of the pointing calibration & reference sensor for SIRTF

We present the performance results of the as-built Pointing Calibration and Reference Sensor (PCRS) for the Space Infrared Telescope Facility (SIRTF). A cryogenic optical (center wavelength 0.55 microns) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from SIRTF's star trackers and gyroscopes to obtain the actual pointing of the SIRTF telescope. The PCRS calibrates out thermomechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-σ radial. The PCRS was installed inside the SIRTF Cryo-Telescope Assembly in July, 2000 and has logged over 1000 hours of failure-free operation ever since. We have verified that the PCRS has survived all box-level environmental requirements, including the 1.4 K operating temperature, random vibration, pyroshock, and EMI/EMC, necessary to survive launch and operations over SIRTF's 2.5 year lifetime. Currently, the PCRS is undergoing testing as part of the recently integrated Observatory in preparation for a January, 2003 launch.