ADAPTIVE ANGULAR VELOCITY ESTIMATOR
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An adaptive filtering technique to estimate the angular velocity is presented for spacecraft with no gyros. The basic idea relies on the fact that, as long as the angular velocity does not change direction, the dynamics of the quaternion describing the attitude evolution, constraints the quaternion itself on a 3-D hyperplane. This paper, using some properties of Ortho-skew matrices and decomposition of orientation into rotations in 4-D space, shows how to identify this hyperplane and how to extract the angular velocity information from a series of subsequent quaternions. Specifically, the direction of the angular velocity is derived from the instantaneous quaternion's plane of rotation while the modulus is estimated by nonlinear leastsquares technique using angles between quaternions. Motivation comes from the possibility to estimate the angular velocity when the spacecraft is erforming fast maneuvers using star trackers data, only, and/or to provide Kalman filters with good initial angular velocity estimates.