Star trackers must be calibrated prior to flight so that they can make accurate measurements of star positions within the instrument field of view. This calibration is often performed in atmosphere and once the sensor is launched, it is not uncommon to observe a small shift in some of the calibration parameters. To maximize sensor performance, these parameter values must be corrected to better match the actual observa tions. In this paper, we explore the several practical strategies for on-orbit recalibration of star trackers. We consider both human-mediated batch-processing as well as autonomous, se quential algorithms. We base our results on orbital data from a number of Sinclair Interplanetary ST16 star trackers launched within the last year. Both approaches to on-orbit calibration can yield significant improvements both to sensor availability and geometric error.
Star trackers are perhaps the most accurate means of measuring a spacecraft's orientation in space and are becoming a popular sensing instrument for attitude determination systems amongst conventional larger satellites as well as micro satellites. In order to produce and maintain high fidelity measurements, the systematic effects of lens distortion and possible sensor alterations due to environmental changes and instrument aging must all be accounted for through calibration, both on the ground and on orbit. In this study, a calibration method is presented to account for errors in star camera parameters, namely the focal length, bore sight offset, higher order radial distortion terms and the tip and tilt of the detector array in relation to the lens arrangement. This method does not depend on a costly high-precision lab setup; instead it simply employs the star camera images and a star catalogue to calibrate the instrument given reasonable initial estimates. This allows for a reduction in pre-mission calibration requirements and is feasible for an online implementation, allowing the star tracker to calibrate itself through out its life-cycle.
Star trackers are perhaps the most accurate means of measuring a spacecraft's orientation in space and are becoming a popular sensing instrument for attitude determination systems amongst conventional larger satellites as well as micro satellites. In order to produce and maintain high fidelity measurements, the systematic effects of lens distortion and possible sensor alterations due to environmental changes and instrument aging must all be accounted for through calibration, both on the ground and on orbit. In this study, a calibration method is presented to account for errors in star camera parameters, namely the focal length, bore sight offset, higher order radial distortion terms and the tip and tilt of the detector array in relation to the lens arrangement. This method does not depend on a costly high-precision lab setup; instead it simply employs the star camera images and a star catalogue to calibrate the instrument given reasonable initial estimates. This allows for a reduction in pre-mission calibration requirements and is feasible for an online implementation, allowing the star tracker to calibrate itself through out its life-cycle.
<p>Star trackers must be calibrated prior to flight so that they can make accurate measurements of star positions within the instrument field of view. This calibration is usually performed in atmosphere and after the sensor is launched; it is not uncommon to observe a small shift in some of the calibration parameters. In this paper, we explore several autonomous strategies for on-orbit recalibration of star trackers. We present an improved version of a popular camera model, develop optimizations to identify optimal parameter values, and validate performance using the data collected from on-orbit sensors. When compared with human-mediated batch processing, autonomous methods have comparable reliability, performance, and commissioning time. The sensor datasets used in this paper come from six Sinclair Interplanetary ST-16 star trackers launched between November 2013 and July 2014. Both batch and autonomous approaches to on-orbit calibration yield improvements in measurement availability as well as a 20%-80% reduction in residual geometric error compared to ground calibrations.</p>
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