Integrating BDS And GPS For Precise Relative Orbit Determination Of LEO Formation Flying

With the development of small satellite technology,low earth orbit(LEO)satellite formation flying has been widely applied in many kinds of space geodesy,become one of the hot issues of aerospace research at home and abroad.Precise relative orbit determination(PROD)of LEO satellites formation flying is a prerequisite for science mission.It is prospective to improve the precision and reliability of PROD to promote the performance of both systems and expand the field of relative applications.This thesis mainly focuses on PROD of LEO satellites formation flying.The contributions are summarized as follows.(1)The contribution of BeiDou satellite navigation system(BDS)to the accuracy and reliability of PROD of LEO satellites formation flying based on global positioning system(GPS)is studied by simulation method.Firstly,when adding BDS to GPS,the mean number of visible satellites increases from 9.71 to 21.58.Secondly,the results show that the 3-dimention(3D)accuracy of PROD based on BDS-only,GPS-only and BDS+GPS is 0.74 mm,0.66 mm and 0.52 mm,respectively.which increased by 29.73% and 21.21%after combining BDS and GPS if only taking the observations noise into consideration.In addition,geostationary earth orbit(GEO)satellites and inclined geosynchronous orbit(IGSO)satellites only distributed over the Asia-Pacific region,but they could provide global improvement to the PROD.Furthermore,the value of ambiguity dilution of precision(ADOP)based on BDS+GPS decreased by 7.50% and 8.26%,compared with which based on BDS-only and GPS-only.Finally,if the relative position between satellites would be only a few kilometers,the effect of ephemeris errors to PROD could be ignored.However,for several hundred kilometers separation of the LEO satellites the single difference(SD)ephemeris errors of GEO satellites can be in the order of centimeters.(2)Based on National University of Defense Technology(NDT)and Xi'an Research Institute of Surveying and Mapping(CHS),we try to identify the time during which the accuracy of the baseline is lower by inter-agency comparison,and to improve the accuracy and reliability of the baseline by inter-agency fusion.The GPS observations data of Gravity Recovery and Climate Experiment(GRACE)satellites are processed by NDT and CHS using different software packages and reduced-dynamic baseline solutions,which promise the generated baseline products are independent.The results show that inter-agency comparison can exactly identify the time during which the accuracy of the baseline is lower than others.And a high consistency level between NDT and CHS.The percentage of differences between the GRACE relative position from NDT and CHS in 3-dimensional less than 2mm is about 97.86%,indicating that there is no obvious systematic deviation between them.Furthermore,it is shown that fusion of the baseline products can reduce the error of random fluctuations,compared to the NDT and CHS products,the precision validated by K/Ka-Band Ranging(KBR)observations of the fused baseline products is improved by 8.97% and 29.21%,respectively.