The advancing state-of-the-art in second generation star trackers

Until recently, only first-generation charge coupled device (CCD) spacecraft star trackers have been available. These track a small number of bright stars and are dependent on external processing for acquisition, calculation of corrections and transformation from CCD referenced to inertial referenced coordinates. Now, powerful microprocessors (>10 million instructions per second (MIPS)) with a few Mbytes of memory have become available in space qualified grades and have enabled the next step in star tracker concepts: second-generation fully autonomous designs. These second-generation units are equipped with star catalogs covering the entire sky. Their microprocessors instantly perform acquisition by pattern recognition of the entire image, thus relating the output from the star tracker directly to the celestial sphere. Their output data can be used in the attitude control system of a spacecraft without intermediate data processing. This saves central processor load, memory capacity and integratation of thousands of line of source code. The use of a large number of stars in each data frame makes the attitude estimates more accurate and operation both smoother and more robust in comparison to first-generation star trackers.