Satellite Angular Rate Estimation from Vector Measurements

Analgorithm ispresented forestimating theangularratevectorofa satellitethat isbased on the timederivatives of vector measurements expressed in a reference and in body coordinates. The computed derivatives are fed into a special Kalman e lter, which yields an estimateof the spacecraft angularvelocity. Thise lter, an extended interlaced Kalman e lter (EIKF), is an extension of the interlaced Kalman e lter (IKF) presented in the literature. Like the IKF, the EIKF is a suboptimal Kalman e lter that, although being linear, estimates the stateof a nonlineardynamic system. It consists of two or three parallel Kalman e lters whose individual estimates are fed to one another and are considered as known inputs by the other parallel e lter (s). The nonlinear dynamics stem from the nonlinear differential equation that describes the rotation of a three-dimensional body. Tests using simulated as well as real Rossi X-Ray Timing Explore satellite data indicate that the algorithm works satisfactorily.