Calibration Techniques for Low-Cost Star Trackers

This study presents a series of cost-e_ective strategies for calibrating star trackers for microsatellite missions. We examine three such strategies that focus on the calibration of the imaging detector, geometric lab calibration, and optical calibration due to lens aberrations. Procedures are developed that emphasize speed of implementation, and accuracy, while trying to minimize manual setup procedures. Preliminary results show that employing existing camera calibration techniques reduces the variation in pixel sensitivity by approximately 10%, averaged across each pixel color given the use of a color imager. Although not substantial, this reduction in pixel variation helps preserve the Gaussian illumination pattern of imaged stars, aiding in correct centroid location. Results pertaining to the lab calibration show accurate star placement, in angular terms, to 4:3_10�3rads across most of the _eld of view. This provides an accurate, low-cost, variable solution for characterizing sensor performance; speci_cally pattern matching techniques. Finally, we present some initial results from lens aberration characterization. Using a Gaussian model of the star image shape gives trends consistent with astigmatism and _eld curvature aberrations. Together, these calibrations represent tools that aim to improve both development and manufacture of modern microsatellite star trackers