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Paper: Kalman Filtering in Chandra Aspect Determination
Volume: 238, Astronomical Data Analysis Software and Systems X
Page: 471
Authors: Hain, R.; Aldcroft, T. L.; Cameron, R. A.; Cresitello-Dittmar, M.; Karovska, M.
Abstract: The ability of the Chandra X-ray Observatory to achieve unprecedented image resolution is due, in part, to its ability to accurately reconstruct the spacecraft attitude history. This is done with a Kalman filter and Rauch-Tung-Striebel (RTS) smoother, which are key components of the overall aspect solution software. The Kalman filter/RTS smoother work by combining data from star position measurements, which are accurate over the long term but individually noisy, and spacecraft rate information from on-board gyroscopes, which are very accurate over the short-term, but are subject to drifts in the bias rate over longer time scales. The strengths of these two measurement sources are complementary. The gyro rate data minimizes the effects of noise from the star measurements, and the long-term accuracy of the star data provides a high-fidelity estimate of the gyro bias drift. Analysis of flight data, through comparison of observed guide star position with expected position and examination of the reconstructed X-ray image point spread function, supports the conclusion that performance goals (1.0 arcsecond mean aspect error, 0.5 arcsecond aspect error spread diameter) were met.
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