A Study Of Reduced-dynamic Orbit Determination Using Undifferenced Observations Onboard GPS For Earth Satellites

With the development of space technology, Precise Orbit Determination (POD) of Low Earth Orbiter satellites (LEOs) based on Precise Point Positioning (PPP) technique has become one hotspot. The principle, mathematical model and mechanical model of reduced-dynamic orbit determination (OD) of LEOs based on PPP are systematically studied in this paper. Utilizing the real GPS observations from CHAMP satellite, the data pre-processing problem, the effect of modeling errors and the impact of pseudo-stochastic pulses on orbit accuracy are discussed in detail. The contributions of this paper are summarized as follows..The composition, method and principle of the orbit determination system based on onboard GPS are simply described. The error sources and their corresponding correction measures are systematically analyzed. Then the GPS satellite equation and variational equation are given..The data pre-processing problem in orbit determination of LEOs based on onboard GPS is chiefly studied. Based on several data pre-processing methods, an efficient method——improved "Majority Voting" algorithm is put forward to detect outliers in GPS observations. The results show that this method has high automatization and good pre-processing results, therefore can obtain high accuracy orbit determination.. The impacts of different mechanical model on reduced-dynamic OD accuracy are analyzed and compared. Especially the impact of different gravity model with different order and degree on reduced-dynamic OD accuracy are mainly analyzed. Then draws some useful conclusions..The impact on orbit determination accuracy of LEOs of different satellite ephemeris and clock errors are studied and analyzed. The results show that the orbital results based on GPS ground tracking stations of using the estimated 30 seconds precise clock errors and final ephemeris are highest..The definition, principle and mathematical model of pseudo-stochastic pulses are systematically studied. The absorption and adjust effect of pseudo- stochastic pulses with different intervals and prior variance on modeling errors in reduced-dynamic OD are studied and analyzed. The optimum orbital parameters are given..The principle and mathematical model of reduced-dynamic OD based on onboard GPS are discussed in detail. Then real GPS observations from CHAMP satellite are used to illustrate OD accuracy of different OD methods so as to study the OD accuracy that each OD method may achieve. The results indicated that the accuracy of dynamic OD accuracy is worst. The accuracy of reduced-dynamic OD method based on geometric and dynamic information, whose is within 10 centimeters, is relative high. The kinematic method, whose accuracy lies between that of dynamic method and reduced-dynamic, has the corresponding OD accuracy to the reduced kinematic one.