An autonomous navigation method for GEO satellites using X-ray pulsars

An autonomous navigation method for GEO satellites is presented. This method takes advantage of the characteristics of GEO satellites to overcome the shortcoming of the X-ray pulsar measurements: The satellite´s orbit dynamics equation is built up in the Earth-fixed reference frame, so that the equation is weakly non-linear and the extended Kalman filter (EKF) is used in this method in spite of the long observation time of X-ray pulsars. Based on the geopotential model, the obit dynamics equation expressed in the Earth-fixed frame is obtained. The phase measurements of X-ray pulsars are used by EKF to best estimate the satellite´s position and velocity. Numerical simulation is done. It is shown that the navigation results attain convergence quickly if the X-ray pulsar measurements are introduced into the estimation, and the accuracy during the intervals without pulsar measurements is also at a satisfying level.