A stellar gyroscope is a star based attitude propagator that is capable of propagating a spacecraft’s attitude in threedegrees of freedom by tracking the motion of the stars in an imager's field of view. The modeling and algorithmdevelopment has been done by the Space Systems Laboratory at the University of Kentucky. This paper discusses arealization of the stellar gyroscope concept on a CubeSat attitude determination and control system (ADCS)designed by SSBV Space & Ground Systems UK. The stellar gyroscope can be used to measure attitude changesfrom a known initial condition without drift while sufficient stars are common across frames, because absoluteattitude changes are measured and not angular rates. Algorithms to perform the star detection, correspondence, andattitude propagation are presented in this paper. The Random Sample Consensus (RANSAC) approach is applied tothe correspondence problem which is challenging due to spurious false-star detections, missed stars, stars leaving thefield of view, and new stars entering the field of view. The CubeSat attitude determination and control systemdescribed in this paper uses a stellar gyroscope, implemented using inexpensive optics and sensor, to augment aMEMS gyroscope attitude propagation algorithm to minimize drift in the absence of an absolute attitude sensor. TheMEMS device provides the high frequency measurement updates required by the control system, and the stellargyroscope, at a lower update rate, resets the drift accumulated in the MEMS inertial gyroscope integrator. This ineffect could allow sun-sensing satellites to maintain a high quality attitude estimate in eclipse, where the sun sensorscan no longer contribute in absolute attitude estimates. This paper describes an algorithm to solve the relativeattitude problem by identifying the change in attitude between two star field images. RANSAC is applied to solvethe correspondence problem in the presence of false star detections and misses. The camera and attitudedetermination and control system are described, prototype hardware is used to generate night-sky datasets of knownattitude changes to demonstrate the performance of the algorithm, and a simulation is developed to evaluate thestellar gyroscope’s ability in limiting the drift of an attitude propagator based on MEMS gyroscope rates. TheCubeSat ADCS system developed by SSBV is an experiment on TechDemoSat-1, to be launched in early 2013.
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