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我国将于2020年首次发射由轨道器和火星车组成的火星探测器.火星探测器的跟踪及精密测定轨是完成工程任务和科学探测的前提.本文首先分析了火星探测器跟踪技术.然后在简述好奇号火星车VLBI观测频度和测定轨精度的基础上,以2020年7月发射的火星探测器为例,给出了深空机动、近火制动、平面机动、降轨前等关键测控弧段的太阳等离子体时延、各测站观测仰角等参数.分析了我国VLBI网对火星探测器的测定轨能力以及关键弧段的测定轨精度.用5 d的测距测速数据、测速测距+VLBI数据分别进行定轨并预报2 d至近火制动点,三维定轨误差(1σ,下同)由只用测速测距时的45.7 km降至18.8 km,近火点高度预报误差由28.2 km降至7.6 km,体现了VLBI在近火制动等关键测控弧段对定轨和轨道预报精度提高的贡献.在测距、测速和VLBI时延测量误差降低后,近火制动段定轨和预报误差会进一步降低.
China will launch for the first time a Mars rover composed of orbiter and rover in 2020. Tracking and precise orbit determination of Mars rover are the prerequisites for completing engineering tasks and scientific exploration.This paper first analyzes the Mars rover tracking technology and then On the basis of the observation frequency of VLBI and the accuracy of the orbit, the Mars rover launched in July 2020 is given as an example to illustrate the effects of deep space maneuver, near fire brake, plane maneuver, Key plasma arc delay of the monitoring and controlling arc, observation elevation of each station and other parameters.Analysis of the orbital capability of the VLBI network to the Mars rover and the accuracy of the orbit determination of the key arc are given.Using 5 d range-measuring speed data, Velocity measurement + VLBI data were respectively fixed and predicted 2 d to near-fire brake point. The three-dimensional orbit determination error (1σ, the same below) was reduced from 45.7 km to 18.8 km when using only the measured distance, The error is reduced from 28.2 km to 7.6 km, which reflects the contribution of VLBI to the orbit prediction and orbit prediction accuracy improvement in key control arcs such as near-fire braking. After the measurement error of the range, velocity and VLBI delay decreases, Dynamic segment orbit and forecast error will be Further reduced.