Constraint estimation of spacecraft positions

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The constrained Kalman filter is implemented for spacecraft formation-flying absolute positions estimation. The orbital motion of a spacecraft is characterized by two range extrema (perigee and apogee). At the extremum, the rate of change of a spacecraft's range vanishes. This motion constraint can be used to improve the position estimation accuracy. The application of the constrained Kalman filter at only two points in the orbit causes filter instability. Two variables, α and β, are introduced into the constrained Kalman filter to maintain the stability and improve the estimation accuracy. Anextended Kalman filter is implemented as a benchmark for comparison with the constrained Kalman filter. Simulation results show that, with proper selection of α and β values, the constrained Kalman filter provides better estimation accuracy as compared with the extended Kalman filter. In this paper, two scenarios are studied. In the first scenario, a spacecraft's absolute position is estimated by assuming the availability of radar measurements. In the second scenario, spacecraft formation absolute positions are estimated. It is assumed that the spacecraft formation is equipped with a Wireless Local Positioning System, which provides the relative-position measurements between spacecraft in the formation. Only relative measurements are assumed in this paper. Copyright © 2011 by Shu Ting Goh.

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Journal of Guidance, Control, and Dynamics