Orbit Determination For Single Navigation Satellite And Lunar Explorer

After the Global Position System—GPS in the U.S.A,GLONASS in Russia andGalileo navigation plan in the Europe, The China is also preparing to construct ourown next Global Navigation Satllite Systerm. The orbit information of the navigationsysterm satellite is need for users' orientation and the relative error will utimatelyinfect the actual users' orientation precision.In the method of simulation jointing with factuall data calculating, this paperfully discussed the strategy and accuracy of orbit determination for single satelliteusing the carder phase and pseudo-range data, without the aid of time synchronizationsystem. We adopted the epoch-difference approach to eliminate the dominant terms ofclock errors, by transforming the pseudo-range and phase data into equivalent integralDoppler data, for which we established the simple measurement model. Simulationstudies indicated that this orbit determination strategy for one satellite works availablywithout knowing either satellite clock parameters or receiver clock parameters. Inorder to confirm the feasibility and the accuracy of the strategy, we try to performorbit determination for one GPS satellite, analyzing error sources such as data arclengths, distribution of tracking networks, observation type choices, observationaccuracy and the priori orbital errors. The simulating tool is the software we compiledourselves in the personal computer. The software used for orbit determination is thespace data analysis software package GEODYNⅡdeveloped at Goddard Space FlightCenter, NASA.The result indicates that without the information of the clocks' time differencesbetween the satellite clock parameters and the receiver clock parameters, the RMS ofthe radial errors is better than 10 meters using three days' data of a limited tracking network and the user range error (URE) is at about the same level.In addition, in the Chinese Lunar Exploration Mission 'Chang Er 1', the task oftracking the spacecraft is mainly dependent on the joint tracking network of UnitedS-Band (USB) and Very Long Baseline Interferometry (VLBI) as a supplement, thispaper also analyses the accuracy of orbit determination for Mission orbit and Landingorbit separately not considering both systematic bias and stochastic measurementnoise. Specially, the lunar gravity field which is the leading error source for themission orbit of a lunar spacecraft is discussed, The results indicate that the reduceddynamics method, in which a set of empirical acceleration parameters are estimatedalong with the initial state vector, can improve the accuracy of orbit determination byabsorbing the error of the gravity efficicients. We analyse various error sources thatwould affect the orbital determination accuracy of the lunar orbiter, moreover, theinfluences of observation data types, the orbite type and the elevation of station on theaccuracy of orbit determination have been investigated.