Reduction Of The Instantaneous State Vectors Of Spacecraft Based On VLBI Tracking Data

Under the background of the Chinese lunar exploration Chang'E Project andbased on the methodology and software system of data reduction of the regularastrometric and geodetic VLBI, in this dissertation the reduction of the instantaneousstate vectors of spacecraft by using VLBI tracking data is realized and progress ismade in various aspects including the establishment of analysis model andobservational equations, the analysis of the condition of normal equation, thedevelopment of the practice software system and so on, which promotes a ratheractive role of VLBI teclmique in the domain of deep space exploration, and which isexpected to actually contribute to the real-time orbit monitoring of CE-1 satelliteduring the lunar capture stage with high precision. Compared to the precise andshort-arc orbit determination, the researches in this dissertation are characterized bythe loose requirement on the length of tracking arc, no need on the preciselymodeling of forces exerting on the satellite, geometrically monitoring the quality oftracking data and the orbit of spacecraft in the way of real-time and with highprecision. It satisfies the requirement of Chang'E Project on high efficiency andquickness.The research progress in this dissertation is as the followings.1) The characteristics are analyzed concerning the features of emitted signal ofextragalactic radio sources versus spacecraft, the model and mode of VLBIobservation, the correction of observation errors, the solving for the mnknowns,the requirement of time-lag on data processing, the present state of analysissoftware systems and so on.2) Through analysis it is recommended that, in case of the unavailable observationsof S/X dual bands, to use observations from a GPS receiver with particularlydesigned sampling settings and supplement analysis software to correct theionosphere effects in the VLBI observations of spacecraft. Our comparison ofGPS observations with those of VLBI indicates that, systematic bias up toseveral hundreds of nonaseconds could exist between the derived baselineionosphere corrections from the two kinds of observations, and the bias couldjump and change versus the observation epochs and elevation angles. The strategic measures are discussed for using supplementary GPS observations tocorrect the ionosphere effects under various circumstances.3) The methodology is analyzed and the practice software is developed for thereduction of the instantaneous state vectors of spacecraft based on VLBI trackingdata. Specifically, the aspects include the establishment of mathematical modelsand the deduction of partial derivatives; the precise prediction of spacecraft statevectors from initial orbit elements, the calculation of state vectors of trackingstations with various geophysical corrections, the iterative computation of thetraveling time of photon and the theoretical observation of VLBI; the necessityof the interpolation operation to observation series as well as the method andvalidity are analyzed in the reduction of state vectors of spacecraft; thediscussion on the conditions of normal equation, especially on the use ofconstraints of distance and rate as well as synthetically processing observationsof range and Doppler; the development of the practice software system; theexamination on the methodology and software based on data simulation.4) The methodology and software are further checked through processing data ofexperimental observations of geo-satellite and lunar satellite, the data processingin the real-time mode is especially enforced and the cross-check with pertinentsoftware is performed. The effect of the distance constraint on the solution andprecision of unknowns is analyzed through theoretical reasoning and solutioncomparison of various combinations of observations.5) The possible application of the Helmert variance component estimation to thereduction of state vectors of spacecraft is discussed, which shows that thismethod significantly improves the solution precision when the formal errors donot correctly represent the actual precision of observations.6) Based on our independently developed real-time data processing software, thedesigned satellite orbit of CE-1 and the present precision of VLBI and USBtracking data, the real-time reduction of instantaneous state vectors of spacecraftduring the orbit maneuver stage nearby the perilune is analyzed via simulationdata and experimental observations. The results show that it is a quick andpracticable method to monitor and identify the lunar capture orbit of CE-1satellite by real-time reduction of the instantaneous state vectors.As shown in the following aspects the researches in this dissertation areurgently expected to be improved and supplemented.1) The method and software still require further checks by simulation data andcross-checK Wltlh related soltware such as Geodyn,OCCAM and Calc/Solve inorder to disclose burgs and limitations.2) Add the processing for the correction of observation errors, especially thesolving tor the quasi-clock correction from observations or extragalactic radiosources with precisely determined coordinates, in order to improve the presentsoftware on the systematic completeness and applicable scope. 3) Improve the processing of observations of differential and phase referencingVLBI and test the software by experiments.4) Make preparation for the method and software concerning the possibleapplication of the geometric reduction or instantaneous state vectors to thelinkage of reference frames, the determination of lunar libration parameters aswell as the reduction of observations of same-beam VLBI.5) Add new modules to automatically identify the central celestial bodies besidesthe Earth-Moon system and the pertinent figure perturbations.6) Apply Kalman filtering to the reduction of the instantaneous state vectors ofspacecratt and develop reductin sottware.There is progress in this dissertation concerning the reduction of theinstantaneous state vectors ot spacecratt based on VLBI tracking data, while thereare also issues urgently requiring solutions and settlements.