基于我国VLBI网航天器定位归算仿真分析

结合我国VLBI观测网现状，通过仿真计算分析了观测时延噪声与系统差、预报轨道偏差和测距误差等对航天器定位归算的影响。结果表明，仅利用VLBI跟踪时附加飞行器地心距约束有利于压制定位点的弥散。 3站 VLBI跟踪的定位解是有偏估计，4站跟踪时要求所加约束的误差应与预报轨道偏差相当，若过大将起不到压制定位点弥散的良好效果，若过小则会在定位结果中引入系统偏差。时延与测距的观测噪声主要引起定位点序列的弥散。若观测量存在系统差则将引起定位结果的系统性偏差，而且定位点序列会发生渐近线性趋势跳变。同时，这也可以作为观测量是否存在系统差的判据。另外，若某时刻前后VLBI跟踪站存在3、4站变更，定位点序列有时发生趋势变化。分析结论对于我国后续探月和萤火计划等工程实践具有借鉴意义。

Simulation Analysis of Positioning Reduction of Spacecraft as per the Chinese VLBI Network

According to the current status of the Chinese VLBI network and through data simulation, the effect of the orbit prediction error, the white noise and systematic errors in VLBI delays and ranging errors on the positioning reduction of spacecraft is analyzed. Results show that it is preferable to suppress the dispersion of positioning data points by applying constraint of geocentric distance of spacecraft when there is only VLBI tracking data. The positioning solution with observations of three VLBI stations is a biased estimate. For the case of four tracking stations the uncertainty of the constraint should be in accordance with the orbit prediction error. If the uncertainty is too large then the effect of suppression on the dispersion of positioning points would be limited. If it is too small then some systematic offset would be led into the positioning results. White noises in delay and ranging mainly result in dispersion of positioning data points. While systematic errors in observations result in systematic offsets in the positioning results, and there are trend asymptotic line jumps in the sequence of positioning points, which could also be taken as a criterion for the existence of systematic errors in observations. In addition, at the moment when VLBI stations change from three to four or vice versa, there may exist the trend jump in the sequence of positioning points. The analysis in this paper could provide a reference for the positioning reduction of spacecraft in the follow|on lunar exploration and the Yinghuo project.