A Study Of The Reduced-dynamic Orbit Determination Of CHAMP Satellites Using GPS Zero-difference Observations

Since LEO satellites have been used for special purposes and earth science researches' needs in recent years, it is widely used in earth gravity field recovery, precision marine geoid and the field of remote sensing imaging while LEO satellite precision orbit is the prerequisite of applications. Since LANDSAT-4 satellite was successfully equipped with GPS satellite receivers, onboard GPS receivers have become the most commonly instruments on LEO satellite. Our country is developing the autonomous navigation system while is also active in a series of LEO satellites experiments. So it has a strong practical significance in determinating the orbits of low orbit satellite based GPS navigation satellites. This paper focuses on the LEO satellite orbit determination theories, techniques and method research, the main research work is as followed:1. This paper reviewed satellites orbit determination based on the tracking technologies and orbit determination methods, focusing on the CHAMP, GRACE and GOCE gravity LEO tasks and analysing the three tasks with orbit determination methods and the accuracy of orbit determination. Based on the analyses this paper determines the focus of this study.2. This paper analyses the quality of GPS observations collected by onboard GPS receiver, which provides a basis for data pre-processing. In this paper, cycle slips and gross errors are detected, repaired and marked by automatic editing algorithm for zero-difference observations, and on this basis, using carrier phase smooth pseudoranges. Due to the accuracy limitation and stability of automatic editing algorithm for the cycle slip and gross error detection, using the COMBINED algorithm can obtain reliable phase data in double-difference mode.3. Introduced the equations of motion and the observation equations of reduced-dynamic orbit determination and analysed the satellite dynamic model and error sources in observation equations; How to obtain the initial orbital parameters is given in this paper; It focuses on the integration processes of motion equations and variational equations using Collocation numerical orbit integration method and verifies the validity of this method.4. This paper researched the key technology of reduced-dynamic orbit determination-pseudo random pulses and introduced the definition of pseudo random pulses and its mathematical model. This paper presented the detail steps of reduced-dynamic orbit determination and given the elimination parameter method and LU decomposition method of parameter estimation theory. It also introduced the selection of weight matrix of observations.5. Based on the above theories and effective methods of LEO satellites orbit determination, this paper analysed the impacts of earth gravity field on orbit integration and analysed the GPS satellites ephemeris and clock errors in orbit determination. It also studied the impacts of satellite elevation angle on orbit determination. At last, single point positioning, dynamic orbit determination method and the reduced-dynamic orbit determination method were carried out for four days (DOY126-DOY129 in year of 2008) with CHAMP satellite orbit determination. Using the pseudo range of single-point positioning can achieved the precision from a few of meters to sub-meter level; It can achieved the accuracy of 0.172m,0.267m and 0.131m in RTN directions respectively by dynamic orbit determination method; It can achieved the accuracy of 0.078m, 0.108m and 0.072m in RTN directions respectively by reduced-dynamic orbit determination method.