An approach of autonomous navigation for satellites using magnitude of the geomagnetic field is presented in this paper. This system works only with a three-axis magnetometer groupware to measure the magnitude of the geomagnetic field intensity. The differences between the measurement values from the magnetometer and the estimated data according to the international geomagnetic field model are used as basic navigation information. Due to the non-linearity of the dynamics equations of satellites and measurement equations of the magnetometer groupware, an Extended Kalman Filter (EKF) is designed to estimate the satellites' position and velocity and to deduce minimum errors. Herein, the state vector consists of six variables, which are distance between earth's center and satellite centroid, colatitude, east longitude, inertial velocity, heading angle and flight path angle. At last, simulation for a sun―synchronous orbit satellite is done. Meanwhile, the effectiveness and practicability of the autonomous navigation method using the magnitude of geomagnetic field vector have been shown.
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