Generation and Validation of On-board Star Catalog for Resourcesat - I Star Tracker

*† ‡ § ** †† ‡‡ The selection of stars for the flight catalog of RESOURCESAT-I star tracker is based on the instrument magnitude (mI). The catalog contains 898 stars with a sensitivity up to 5.0 mI. It is generated from 13 color photometric data. For stars for which the photometric data are not available, red pass band magnitudes of Skymap2000 catalog are used. The photometry method is validated by generating visual magnitudes and comparing them with the Skymap2000 catalog visual magnitudes. It is expected that the predicted instrument magnitudes are within 0.1 magnitude for the photometric method and within 0.2 magnitude for the method using the red pass bands. Flight results indicate that the residuals between the observed and the predicted magnitudes are lower than 0.1 mI ( one sigma) for the method using 13 color photometry and within 0.2 mI for the method using red pass bands and these meet the mission requirements. HE Indian Remote Sensing Satellite Resourcesat-I carries two autonomous star trackers that provide 3-axes and lost-in-space attitude determination. Each tracker has a 20° x 20° field of view and uses an MPP area array charge-coupled device as the optical sensor. Each CCD consists of 1024 x 1024 pixels, each of size 17 µm x 17 µm. The star trackers give attitude information on successful identification of the stars present in the field of view through comparisons of observed angular separations and magnitudes with those contained in an on-board star catalog. Such a catalog is generated by a systematic selection criterion to optimize the memory requirement and the star availability for maximum duration. For accurate determination of attitude, the star catalog contains stars that can be sensed by the star tracker. Hence, the selection of stars for the on-board catalog is based on instrument magnitude (mI). The onboard catalog for Resourcesat-I contains 898 stars up to 5.0 mI with sensitivity up to 5.5 mV (visual magnitude). At least four stars are always present in the field of view for any given orientation of tracker.