Hybrid precision orbit determination for low altitude satellites by GPS tracking
MetadataShow full item record
A numerical simulation study was performed in order to investigate the effects of process noise modeling on state estimates of a Low Earth Orbiting (LEO) satellite in the GPS-based hybrid Precise Orbit Determination (POD) strategy. The use of simulated data enabled the creation of the simulated data with three different correlation types of the unknown forces, which were constant in magnitude, exponentially decreasing and periodical with exponential decrement. The hybrid POD results obtained with first order Gauss-Markov random process and periodic random process were mutually compared to assess their relative performance under the same condition. The simulation results indicate that the hybrid POD strategy with a periodic random process provides an improvement over that with a first order Gauss-Markov random process for the three cases studied, particularly for the unknown force with periodical behavior. Application of the hybrid POD strategy to the CHAMP satellite was conducted. The CHAMP GPS tracking and a ground station network of thirty-five GPS tracking stations were processed to yield a five day CHAMP ephemeris. The hybrid POD results obtained from processing the real CHAMP tracking data showed the improved performance of periodic random process over first order Gauss-Markov random process. Measures such as orbit comparison with other high accuracy orbit solutions and SLR residual analysis were taken to assess the radial orbit accuracy of the hybrid orbit solution. As a relative measure of orbit accuracy, the orbit comparison of the hybrid orbit solution to the MSODP reference orbit solution was made and the results indicate that the radial orbit accuracy of the hybrid solution is within 6 cm in an RMS sense. As an absolute measure of orbit accuracy, the SLR residual analysis was performed and the results indicate that the radial orbit accuracy of the hybrid solution is at the level of 3 - 4 cm RMS, for the CHAMP orbit with 460 km altitude.