The Validation and Accuracy Analysis of BDS Solar Radiation Pressure Models

Abstract

The solar radiation pressure?SRP?perturbation is difficult to be accurately modeled so that it becomes the most important error source in the precise orbit determination POD and forecast of GNSS satellites. BDS is Chinese GNSS system BeiDou Satellite Navigation System and it has completed its Phase I plan. There are 16 satellites in service since the first BeiDou experimental satellite launched in 2007. BDS’s next step is to set up the global BDS with 3GEO +3IGSO +24MEO (Maybe it will be 5GEO + 3IGSO + 27MEO) before 2020. 2IGSO+2MEO experiment satellites have been launched till now. The global BDS is designed to obtain the similar accuracy of GPS. Therefore, high accuracy BDS solar radiation pressure models must be set up. A box-wing theoretical SRP model with fine structure and adding conical shadow factor of earth and moon were established. We verified this SRP model by the GPS Block IIF satellites. The calculation was done with the data of PRN 1, 24, 25, 27 satellites. The results show that the physical SRP model for POD and forecast for GPS IIF satellite has higher accuracy with respect to Bern empirical model. The 3D-RMS of orbit is about 20 centimeters. The POD accuracy for both models is similar but the prediction accuracy with the physical SRP model is more than doubled. We tested 1-day 3-day and 7-day orbit prediction. The prediction arc length is longer the improvement is more significant. The orbit prediction accuracy with the physical SRP model for 1-day, 3-day and 7- day arc length are 0.4m, 2.0m, 10.0m respectively. But they are 0.9m, 5.5m and 30m with Bern empirical model respectively. Moreover, we also test to estimate two solar pressure coefficients for satellite body and wing respectively. We hope it can give better results because the body and wing of satellites use different characteristic materials. We apply this means to the BDS and give out a SRP models for Beidou satellites. These BDS BOX-wing theoretical SRP models are adjusted to fit BDS measure data. In the process of Box-Wing modelling for similar cuboid satellite, six faces of main body and two solar panel are considered separately. The direct solar radiation model is related to shapes of different parts, area, reflectivity, specularity, orbital angle, and directions in the Body Fixed coordinate System. The absorption and diffuse reflection coefficient are estimated in the direction of each panel, specular reflection coefficient, and scaling factor, Y-axis bias, and B-axis experience parameters. At first we have estimated 15parameters. But we found that the correlations among some of the parameters are very strong. So strong related parameters are removed and the panels in the same line direction adopt same two comprehensive parameters (absorption plus diffuse reflection part and specular reflection part). We have also tested the nine parameters and six parameters models. Finally, we have choosed a reduced five parameters model with D-scale, Y-bias, solar panel, box-axis and z-axis. The accuracy of these SRP models is validated based on SLR data and BDS orbit prediction. The better SRP model will be helpful to improve the accuracy of Beidou broadcast ephemeris and server better for Beidou positioning. Keyword: BDS, Precise Orbit Determination, MGEX, Solar Radiation Pressure