Precise Orbit Determination And Assessment Of Low Earth Orbitors Based On GPS

This paper focuses on the precise orbit determination (POD) problem of the Low Earth Orbiters (LEOs) using double-frequency observations of the Global Position System (GPS). A simulation platform is built up, which is used to generate the satellites-to-satellites tracking data, as a tool to validate the algorithm developed for the future application of GPS sensors on the LEOs. The geometry strategy of POD using carrier phase epoch-wise differency and P code is studied by the simulated data in order to achieve the decimeter accuracy level. The accessment method of POD results is also discussed. The contributions of this paper are as follows.Firstly, with the analysis of the CHAMP data, the space environment of LEOs and its influence is discussed. The mathematical models of the delay of the GPS signal in the circumstance are put forward respectively. The computation of orbital arc of the two satellite constellations(GPS and LEOs) is based on two body problem and perturbations models. An algorithm based on the IRI model and thin layer model is used to simulate the ionospheric delay of the GPS signal. The error models of observation, multipath, relativity and antenna phase center bias are also researched. Under the consideration of the autocorrelation of the electronical measurements, the autoregressive model of time series is introduced into the noise models. The receiver clock error models and satellite clock error models are induced from the real data analysis. Further more, the visibility of GPS signal is also analyzed.Secondly, four kinds of POD strategy are investigated, including the dynamic strategy, the kinematic strategy, the hybrid strategy and the geometry strategy. The algorithms using differential data and smooth spline fitting are applied to detect the outliers in GPS data. The Blewitt cycleslip detection algorithm is also evaluated by the simulated data and the application conditions of Blewitt are discussed in this section. The POD algorithm based on pseudo range and carrier phase epoch-wise differency observations is estimated by the simulated data. Based on the calculation results under different weighting and different GPS ephemeris accuracy, the influence of these factors to the POD results and the selection of the weighting are discussed.Finally, the assessment method of POD results is studied, including the assessment principle and method of inner conformity precision and outside conformity precision. Under the assumption of equal errors charits of POD results, the statistical assessment method is established by comparing the GPS POD results with the satellite laser range data.