Research On Centralized Autonomous Realtime Orbit Determination And Time Synchronization Of BDS

Whether owning self-developed NavigationSatellite System is an important sign of national economic, military and political power. The United States, Russia and European Union has started to build GPS, GLONASS and Galileo Navigation Satellite System early or late, to safeguard national security, our country has already started the development of Compass Navigation Satellite System(BDS for short) in1994. so far,16Compass Navigation Satellites has been launched, and the Regional Passive Service Ability, which has been possessed with5GEO,5IGSO and4MEO satellites, is expected to comprise5GEOs and30Non-GEOsGlobal Passive Service Abilityin2020.The satellite’s ephemeris, offered by the Operational Control Segment(OCS) and then broadcasted to the users by satellites, is the very crucial data for navigation and positioning, for its precision determines the performance of Navigation Satellite System. So, Whether Navigation Satellite System run normally depends heavily on OCS. If OCS is brocken or the Master Control Station is destroyed in war, soon the wholesystem will be paralysed. Even under normal operation conditions, the system’s performance will also dependheavily on the number and distribution of the Ground Monitor Station. But, due to politics and environmental circumstance, our country can’t set stations all over the world like the USA. Therefore to develop inter-satellite crosslink and abate GNSS’s dependence on the ground station plays an important role in the realization of Global Passive Service Ability of BDS.The establishment of inter-satellite crosslink means that Navigation Satellite System’s dependence on OCS was released, surviving ability of the system in war or natural disaster was improved, and the impactof Ground Monitor Station’s distribution on the system was depressed. Early in the1980s, research on autonomous orbit determination(AOD) has been developed for GPS. Owning to the sensitivity and confidentiality of the technique of AOD, the foreign public materials on this topic are not only scarce but also seldom mentioned the algorithm kernels and key techniques. Meanwhile, BDS has its own features in the constellation design and the distribution of the ground tracking network, and moreover, we can’t fully imitate the AOD techniques of the foreign satellite navigation system. Therefore, to develop our own global navigation satellite system and ensure its performance and survivability in war, we have to carry out the relevant research on the techniques of BDS-based AOD.Chosen the simulated constellation of BDS as a study target, this paper engaged in a systematic research on the models and algorithms of Centralized Autonomous Realtime Orbit Determination and Time Synchronization, and a simulated analysis software has been developed by myself. Validity and reliability of this software has been proved by a great deal of computions and analysis, some useful conclusions has been reached which provide references for the development of BDS-based AOD as well. In particular,this paper’s works and contributions can be summarized as follows:1、A Small-step and low-order Collocation method is presented for realtime orbit determination, and its calculating performance has been analysed in detail by appling it to two-body problem and GPS constellation. The result indicates that it is viable and effective to adopt small-step and low-order Collocation method to realtime orbit determination when the lenth of step is in a certain range;2、The inter-satellite/satellite-station crosslink observation equation and the inter-satellite/satellite-station one-way observation equation has been derived, and a comparative analysis work has been done to these two kinds of equations theoretically; On this basis, this paper carried out a intensive research on parameter decomposition filter model and parameter integration filter model to analyse the performance of these two models from three aspects which include calculation precision, solution time and correlation between parameters; At last, a half-decomposed parameter filter model, which applies to the situation of one-way satellite-station observations, has been introduced, and futhermore a20-days’ calculation of orbit determination has proved the accuracy and effectivity of this filter model;3、A method, which realized the fusion of inter-satellite and satellite-station observations by using method of Hermert variation component estimation, had been adopted. This method was proved to be accurate and effctive by a simulative calculation on the premise of the detailed algorithm’s presentation;4. Inter-satellite crosslink’s effect on precision of GEO orbit determination has been analysed through simulative checking-calculation, the analysis result shows that precision of GEO orbit determination has improved considerably, systematic property has been reduced to some excent as well as the speed and qulity of convergence been advanced when considering inter-satellite crosslink observations;5、Short-arc orbit determination has been adopted in the recovery of GEO maneuver orbit in the process of Centralized Autonomous Realtime Orbit Determination and Time Synchronization. The result shows that the schedule introduced in this paper can not only recover orbit’s precision of maneuver satellite in a short period of time, but also ensure the continuity of autonomous orbit determination of maneuver satellite;6、On the basis of existing software platform, a simulative analysis software for Centralized Autonomous Realtime Orbit Determination and Time Synchronization of BDS has been developed by myself. This software can accomplish simulation of inter-satellite/satellite-station observations, Centralized Autonomous Realtime Orbit Determination and Time Synchronization, recovery of GEO maneuver orbit and accuracy assessment et al. A lot of calculation and analysis have been conducted to prove accuracy and validity of this software, and some useful conclusions be reached as well.