Research On Very Long Baseline Interferometry Applied To Precise Orbit Determination

In traditional TT&C system, the radar ranging technology and Doppler velocity measurement are used to measure the radial distance and radial velocity of the aircrafts relative to the station, which are the main techniques for spacecraft tracking and track monitoring. But the two radio technologies are not sensitive to vehicle lateral position and lateral velocity. Thus with the increase of vehicle distance, due to the restriction of measuring precision and system error, measurement accuracy expressed in angle will be worse, unable to meet the need of the aerospace measurement and control. Very long baseline interferometry(VLBI) is a kind of radio interference technology, which can achieve high angular resolution, and has played an important role in the field of aerospace measurement and control. This thesis focuses on the simulation of VLBI subsystem of TT & C communication system on lunar exploration satellite, and carries out the following work from three aspects:The thesis describes and compares several pseudo random codes firstly. Describes the principle of m sequence, Gold sequence and JPL code, does the simulation of JPL fast acquisition code, and finally verifies that the capture speed of JPL code is faster than that of m sequence. Combining with the pseudo code ranging principle, puts forward another use of the pseudo random code, namely through the difference of the pseudo code offset of the signals received by two ground stations calculates the estimated time delay between the two stations. Especially sets appropriate code period and code rate for JPL code simulation design, which can meet the accuracy requirements for time delay compensation.The thesis intensively studies the capturing and tracking method of VLBI spread spectrum signal secondly. In view of the long acquisition time of the traditional correlation detection method, studies parallel search acquisition algorithm in frequency domain based on FFT, which changes two-dimensional search of pseudo code phase and frequency into the one dimensional pseudo code phase search; and improves this algorithm for the JPL composite code, then searches phase of each sub code in the complex code in 4 parallel paths, and the simulation verifies the operations of the algorithm greatly reduces. Then does research on incoherent DDLL(Digital Delay Lock Loop) pseudo-code Delay Lock Loop and Costas PLL carrier tracking loop, and the simulation verifies accurate PN code phase and carrier phase are achieved.The thesis intensively studies the VLBI system data processor finally. Considering the need for time delay compensation, puts forward a method by the difference calculation of pseudo code offset of two stations’ received signal to obtain the value of the time delay compensation. Simulink simulation shows that the method is feasible and effective. Afterwards, by observing interference fringe, through the coarse search and fine search the precise time delay value is obtained. Finally, selects three independent baselines’ time delay and uses satellite single point positioning method for calculation of satellite position coordinates.