SATELLITE ANGULAR RATE ESTIMATION FROM VECTOR MEASUREMENTS

An algorithm is presented for estimating the angular rate vector of a satellite that is based on the time derivatives of vector measurements expressed in a reference and in body coordinates. The computed deriva tives-ate fed into a special Kalman filter, which yields an estimate o f the spacecraft angular velocity. This Biter, an extended interlaced Kalman filter (EIKF), is an extension of the interlaced Kalman filter (IKF) presented in the literature. Like the IKF, the EIKF is a subopti mal Kalman filter that, although being linear, estimates the state of a nonlinear dynamic system. It consists of two or three parallel Kalma n Biters whose individual estimates are fed to one another and sie con sidered as known inputs by the other parallel filter(s). The nonlinear dynamics stem from-the nonlinear differential equation that describes the rotation of a three-dimensional body. Tests using simulated as we ll as real Rossi X-Ray Timing Explore satellite data indicate that the algorithm works satisfactorily.