ON-ORBIT CALIBRATION OF PRECISION STAR TRACKER FOR THE ADVANCED LAND OBSERVING SATELLITE (ALOS)

摘要

A precision star tracker was developed for the Advanced Land Observing Satellite (ALOS) that required stringent attitude determination accuracy and has been operated successfully on orbit for 45 months. This first-generation star tracker has three optical heads and provides star position accuracy of 9 arcsec (6 mag) for random error and 0.74 arcsec for bias error. Its precise star position accuracy was enabled by low-thermal distortion structure, tight temperature regulations, high-sensitivity and high-resolution CCD, and precise testing. All functions and performances of this star tracker were verified on orbit in the initial check-out phase. In addition, its performaces have been assessed continuously and if neccessary, calibration have been performed. The calibration parameters have been derived from numerous sets of all pixel data and have been uploaded on orbit five times. As a result, this star tracker alone met its performance requirements, despite a relative alignment change anomaly caused by the satellite structure. This paper describes a part of these flight experiences and calibration results. In particular, sensitivity tuning, star position accuracy, magnitude accuracy, optical performance, South Atlantic Anomaly response, stray light, optical distortion parameter estimation, and relative alignment change anomaly and compensation are reported.