Satellite Orbit Determination Method With DORIS System

DORIS is an advanced ground-based satellites orbit tracking system developed by French. The system can not only provide precise orbits between 1 and 3cm in radial component, but also provide real time orbits better than 1m. However, our country did research on DORIS system very late and known a little about key technologies. This paper studied the DORIS orbit determination method, and mainly researched the DORIS real time orbit determination method. The main work includes 4 parts:Firstly, the DORIS precise orbit determination method is studied. The DORIS measurement equation is showed at first. The rule of the frequency biases between beacons and satellites is presented. Then, this part built the reduced dynamic orbit determination method of DORIS satellites. The orbits of SPOT-5 and JASON-2 this paper determined compared to the precise orbits provided by IDS. The RMS is 2.3cm of SPOT-5 while 2.5cm of JASON-2 in radial component, which reached the international level.Secondly, this part studied the real time orbit determination method, especially under a single channel. This part showed the filter formulations based on Extend Kalman Filter theory. DORIS measurement data are simulated, and the characters of simulated data and real data are analyzed. The experiments show that it is difficult for the filter to converge with the measurements of only one beacon; while it converges quickly when the observation data changed from one beacon to another beacon; the real time orbit accuracy can be improved by adding the channel, but the improved accuracy is limited.Thirdly, this part studied the method to estimate frequency biases in the real DORIS data. This part analyzed errors in DORIS data, and pointed that frequency biases is the max error. Next, this part proposed a method to estimate the frequency biases, while the initial values of that were unknown. Using this method and considering the 40×40 Earth gravitational fields, moon and sun attractions, this part analyzed ten days'measurements data of SPOT-5. The results show that the R,T,N direction and 3D accuracies are 22.3cm,60.5cm,38.5cm and75.4cm. The R direction accuracy is corresponded to the SPOT-5 real time orbit accuracy. Finally, this part proposed a method to optimize the filter parameters by experiment design theory. The experiment index is the accuracy of the real time orbit in 3D, and the experiment factors are the noise variances. It needs to estimate the range of experiment factors at first, and then determine those levels. The experiments show that compared to the normal noise variances the noise variances determined by experiment design theory can improve the orbit accuracy obviously, and the real time orbit accuracy of SPOT-5 is 54cm in 3D which is near to the real accuracy of this satellite.