This paper examines the effectiveness of small star trackers for orbital estimation. Autonomous optical navigation has been used for some time to provide local estimates of orbital parameters during close approach to celestial bodies. These techniques have been used extensively on spacecraft dating back to the Voyager missions, but often rely on long exposures and large instrument apertures. Using a hyperbolic Mars approach as a reference mission, we present an EKF-based navigation filter suitable for nanosatellite missions. Observations of Mars and its moons allow the estimator to correct initial errors in both position and velocity. Our results show that nanosatellite-class star trackers can produce good quality navigation solutions with low position (< 300 m) and velocity (< 0.15 m/s) errors as the spacecraft approaches periapse.
<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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