Orbit Determination of an LEO Orbiter with Less Than Four Visible GPS Satellites

摘要

In this paper, Orbit Determination (OD) algorithm for a Low Earth Orbiting (LEO) satellite is introduced and its performance is analyzed using simulation data. The GPS measurements are applied as observations to estimate the LEO satellite position. This study is focusing on the situation with lack of ranging-measurements. In general, at least 4 GPS satellites are required to estimate positioning solution with GPS data. However, there are some environments which have less than 4 visible GPS ranging data. For example, with an inertial pointed antenna, the number of GPS tracking data decreases, when it goes in the earth's shadow. Moreover, with some satellites the number of GPS data maintains less than 4. To overcome this limitation, satellite dynamics is aided to improve the positioning accuracy. Dynamical Extended Kalman Filter (EKF) is examined to estimate the position, velocity and clock parameters. Dual frequency GPS simulation data is examined. The OD algorithm is for the environment that a GPS receiver in the LEO Satellite tracks less than four visible GPS data. To evaluate this algorithm, we use the simulation data of a cube satellite, a type of miniaturized satellite for space research, which is launched into a sun synchronous orbit at attitude of 600km. As a result, the accuracies of a few decimeters are achieved by dynamical EKF for the simulation data.