Research On The Method Of Adaptive Real-time Relative Orbit Determination Using On-board GPS

Based on “adaptive orbit determination technique”,the real-time relative orbit determination method for formation flying satellites with adaptive Kalman filtering is studied in this paper.Using measured data of GRACE satellites,the accuracy and stability of this method are tested and analysised.The main content and conclusions can be summarized as follows:1.The basic theory of real-time orbit determination with geometric approach are presented.The theory and character of pseudorange smoothing method with carrier-phase,and ionospheric–free orbit determination based on DRVID model are analysed.The tight filtering based on both pseudorange and carrier-phase is realized and test with measured data.The result shows that,compared with pseudorange smoo thing,the precision of filtering based on both pseudorange and carrier-phase is better,while the realize of program is harder.In whole words,the use of carrier-phase will improve the accuracy of point positioning based on pseudorange to at least 4m.2.Based on the character that pse udorange is easily poisoned by noises,the application of robust estimation is dissscussed,and the quality test method of point positioning based on DOP value and chi-square statistics is studied.With half-simulate data,conclusions are made as follows: elevation mask,DOP value and chi-square test,with robust estimation together,can better control the qulity of point positioning.The final accuracy can reach about 4m,and the difference against JPL is within 50 m.3.The impact of dynamic model precision is discussed,and the conclusion is that,earth gravity field model and atmospheric drag are main forces on LEO satellites,the state noise compensation can cover the disadvantage of dynamic model,and the earth gravity field model on 20-30 degree is enough in dynamic smoothing.4.The real-time orbit determination method based on pseudorange is studied,and the characters of extended Kalman filtering(EKF),robust M-M filtering,robust adaptive filtering algorithms and the impact of different filtering parameters are analysised,and the result shows that the robust M-M filtering and robust adaptive filtering can solve the divergence problem existing in EKF,and the relying on state noise schedule is decreased.Compared with the robust M-M filtering,adaptive filtering is easier in realization and calculation.The best orbit determination accuracy is about 4m,and the difference against JPL is within 30 m in X?Y direction and below 40 m in Z derection.5.An adaptive factor model based on PDOP value is put forward and realized.The result shows that,this new model is capable to judge the observation precision,and the calculation of adaptive factor is more flexible and accurate.Compared with traditional model,the new one can acquire a better orbit determination accuracy.6.Based on the adaptive orbit determination theory of single satellite,the adaptive real-time relative orbit determination method for formation flying satellites is studied.The impact of base-line length is researched.Based on pseudorange observations,adaptive real-time relative orbit determination method is realized,and based on carrier-phase observations,the adaptive real-time relative orbit determination method and real-time relative orbit determination method with prior information are realized as well.The result shows that the impact of base-line length is more obvious on EKF than adaptive filtering and the accuracy of adaptive relative orbit determination based on pseudarange and carrier-phase is 9cm and 6cm respectively,in which the real-time relative orbit determination method with prior information is more accurate.