Study On Autonomous Orbit Methoed Of Navigation Constellation Based On ISL

Precise Orbit determination is an important foundation for a satellite navigation system to run properly. Currently, the accurate orbit determination of GPS system is realized through long-term continuous tracking and observing the satellite by globally uniformly distributed observatory, then the precise orbit of each satellite is obtained by GIS analysis and resolving. Due to political reasons, China cannot set observatory all over the world, therefore, precise orbit determination cannot be achieved by long-term continuous observation of BDS. Autonomous orbit determination is the development direction for future navigation systems and an important way for solving the problems in development of Global Navigation of China. Therefore, this thesis concentrates on the key technology of Inter-satellite link autonomous orbit determination and X-ray pulsar auxiliary orbit determination. The unsolved technical problems in combined orbit determination are discussed in detail. Aimed at improving the accuracy of long-term autonomous orbit determination for navigation satellite, two corresponding error control solution are proposed. The main contents are as follows:1. Firstly, based on the space-time model of the satellite orbit, the time system, coordinate system and their inter-conversion which are needed for the autonomous orbit determination for satellite constellation are analyzed. On this basis, the choice of frequency bands between satellites observations are studied in detail. Moreover, aimed at the characteristics of nonlinearity and instability in autonomous orbit determination models, the square root UKF is identified as the orbit determination method for the space-borne filter.2. Secondly, the inter-satellite observation network for the Beidou MEO satellite is designed in detail. According to the characteristics of the two typical band antennas, the constraints on the visibility of inter-satellite observation link from the static and dynamic scanning mode scan mode is discussed. On this basis, two different number of antennas link topology is designed. Based on the designed link structure, the effectiveness of the autonomous orbit determination of the inter- satellite link is verified using the real data and the insufficiency of autonomous orbit determination is analyzed.3. Thirdly, the orbit determination technology based on X-ray pulsar is studied to solve the absolute benchmark problem of autonomous orbit determination of the inter-satellite link. Taking into account the problem of error in the accuracy of orbit determination due to the limitations of pulsars observation technique, the Star Table azimuth error, which is the main error affecting the accuracy of the auxiliary orbit determination, is analyzed and its estimation methods are discussed in detail. An X-ray pulsar orbit determination algorithm based on the Star Table azimuth error is proposed to improve the accuracy of the auxiliary orbit determination.4. Finally, the algorithm based on the combination of Inter-satellite links and X-ray pulsar orbit is explored in depth in this article. Since the data of orbit determination coming from two sets with greatly different precision cannot be fused in Federal Kalman filter, we propose a cascade combination filtering algorithm, using the priori information with absolute reference of the auxiliary orbit determination of the pulsar, instead of the orbit prior information of the autonomous orbit determination of the original inter-satellite link. The effective fusion of the results of two autonomous orbit determination is achieved by adopting the thought of cascade filtering.