Research On Key Technologies Of BDS Precise Orbit Determination

The Bei Dou-2 Satellite Navigation System(BDS) has provided the services of positioning, navigation, timing(PNT) and short-message communication for the Asia-Pacific region since December 27, 2012. The system is designed to cover the global and provide the PNT services for worldwide users around 2020. The orbit product of the navigation system is one of the core elements to guarantee the availability of navigation system. The accuracy of satellite orbit will directly affect the navigation performance of the users. Therefore, how to obtain the navigation satellite orbit with high precision is a key research question which the BDS concerns currently.The BDS of our country consists of three kinds of satellites, includes the satellites in Geostationary Orbit(GEO), the satellites in Inclined Geosynchronous Orbit(IGSO) and the satellites in Medium Earth Orbit(MEO). The unique constellation constitution of BDS makes it more competitive in the PNT services for the Asia-Pacific region. But the different constellation characters bring new challenge to the precise orbit determination. At the same time, there are still many problems of BDS system, such as the under construction satellite system, the no global distribution of tracking stations and so on. These due to the mature techniques of GPS satellite orbit determination can not be used by BDS satellite orbit determination directly. How to solve a number of key technologies which the BDS orbit determination is facing now and get the BDS satellite orbit with high precision have become a serious hotspot to be solved. Based on these, this paper carried out the related research. The main research contents and results are as follows.(1) Summarizing the principles of satellite orbit determination, the method of dynamic orbit determination, the observation mode of navigation satellite orbit determination, the related time systems and coordinate systems and the parameter estimation methods of satellite orbit determination. Especially, the principles and corrections of the primary error sources of orbit determination and their impacts on orbit determination were analyzed.(2) For the different constellation orbital characteristics of GPS, GLONASS, GALILEO and BDS, the methods and strategies of different navigation system orbit determination were formulated. The characteristics and the orbit determination precision of each navigation system were analyzed. And the impacts of various orbit determination error sources on the orbit determination presicion of three kinds of BDS satellites were given. Then the main problem which the BDS orbit determination is facing now was obtained by comparing the orbit determination results of BDS and GPS.(3) The quantitative methods of using the satellite SPDOP values and dynamic parameters DOP values to describe the contribution of the tracking station distribution to orbit determination were proposed. And the related mathematical models were derived. These two methods could directly evaluate the impact of the tracking station distribution on the precision of orbit determination. Then the optimally selected method of the tracking station distribution for the BDS orbit determination could be obtained. The measured data analysis results showed that these two methods could be considered as the optimally selected basis of the tracking station distribution scheme.(4) For the current situation of constellation incomplete of building navigation systems, such as BDS and GALILEO, the method and strategy of combined orbit determination was proposed. The analytical contribution of multi-GNSS combined orbit determination to the solution precision of the common parameters and the non-common parameters between different systems was derived. And using the measured data, the statistical contribution of BDS/GPS combined orbit determination to the solution precision of orbit and clock error was analyzed. The measured data results showed that the contribution of combined orbit determination to the solution precision of the common parameters and the non-common parameters between different systems was significant. The solution precisions of the orbit and clock error were significantly improved except GEO satellites. Especially, the contribution to the clock error of receivers which were in the area with few visible satellites was particularly significant.(5) In order to improve the precision of orbit determination when the satellite is in the overlap portion of the earth shadow and the moon shadow. The shadow function model attending the overlap portion of the earth shadow and the moon shadow was established. And the impacts of the old and new shadow function models for the precision of orbit determination were comparatively analyzed. The result shows that the GPS external and overlapping precision which were obtained by the new shadow function model were improved.(6) In order to obtain the different types of BDS orbit products which have different delays. The solving strategy of each BDS orbit product was designed. And the long time span solving precisions of each BDS orbit products were evaluated. The results showed that the precision of each BDS orbit product was stable in the long time span. the average orbit determination precisions of GEO satellites of each type product were better than 2.5m.And the average orbit determination precisions of IGSO and MEO satellites were better than 10 cm. Especially, the precision of IGSO and MEO final product was better than 5cm.