SOFIA tracking subsystem: Results of assembly, operation, and calibration tests

The SOFIA airborne telescope has a Tracking Subsystem for stellar acquisition, tracking, and pointing. The system has three high-performance imagers: the boresighted wide field (6 degrees FOV) and fine field imagers (70 arcminutes FOV), and the main-telescope-optics sharing focal plane imager (8 arcminutes FOV). The imagers are controlled by 3 CCD head controllers, an overall imager controller, and a tracker controller providing the tracking error signals from the objects observed by the imagers. There have been several test steps in the assembly, integration, and verification of the Tracking Subsystem. ne paper presents the fully integrated system as actually built, the results of the thermal-vacuum and vibration tests of the fine field imager, the tested operational/functional S/W performance, as well as the results of the geometric and radiometric calibrations of the imagers.