Simultaneous Attitude and Orbit Determination Using Sensor Fusion Algorithm Based on the Dynamic of Satellite and Star Tracker

In this paper, simultaneously attitude and orbit determination of satellites using only star tracker measurement is investigated. At first, the 6 D.O.F. governing equation of the system considering the gravity force and gravity gradient torque is obtained using the Newton-Euler equations. Next using a simplified star catalog, star tracker output in the desired orbit is calculated. To estimate variables of the attitude-orbital equations, an estimation algorithm based on the UKF is proposed. In each step using the governing equation, estimated parameter and star tracker output, satellite angular velocity and orientation of body against NED frame are estimated and these calculated parameters are used as input for the next step. According to Results after about one revolution of orbit, the estimation is converging and the ratio of filter’s solution error to dynamic’s solution error for the roll and yaw angles is about 2 percent and for the pitch angle and angular velocities are about 33 percent. In order to reduce position and linear velocity errors, the filter needs more time and at the end of 6 cycles, the performance shows 40 percent improvement in average.