The NEAR spacecraft uses a star tracker for precision attitude determination and employs techniques for autonomous star identification and tracking. Outdoor test data and flight data have been analyzed to characterize the performance. Both types of data show good agreement in general with calibration data. Results from the outdoor tests were used to improve models of the tracker in simulations used for software development and test. This paper briefly describes the guidance and control system and star tracker, simulations, and star catalogs. The remainder of the paper discusses the analysis of the flight data and compares the performance results with calibration data.
An instrument has been designed to demonstrate 5 arc second autonomous, all-stellar attitude determination on a NASA Spartan spacecraft. The instrument includes a CCD star camera that provides centroid measurements of up to 5 simultaneous star images with 10 frames of data per s. The performance of the camera and processing techniques have been studied in an extensive test program including star measurements taken under realistic conditions at the Jet Propulsion Laboratory Table Mountain Observatory. Results of these tests are presented and compared to laboratory and simulation data. At slue rates less than 0.1 deg/s the camera accuracy was found to vary from 5 to 15 arc seconds per image, depending on star magnitude.