Integrating BDS and GPS for precise relative orbit determination of LEO formation flying

Low-Earth-Orbit (LEO) formation-flying satellites have been widely applied in many kinds of space geodesy. Precise Relative Orbit Determination (PROD) is an essential prerequisite for the LEO formation-flying satellites to complete their mission in space. The contribution of the BeiDou Navigation Satellite System (BDS) to the accuracy and reliability of PROD of LEO formation-flying satellites based on a Global Positioning System (GPS) is studied using a simulation method. Firstly, when BDS is added to GPS, the mean number of visible satellites increases from 9.71 to 21.58. Secondly, the results show that the 3-Dimensional (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. When BDS co-works with GPS, the accuracy increases by 29.73%. Geostationary-Earth-Orbit (GEO) satellites and Inclined Geosynchronous-Orbit (IGSO) satellites are only distributed over the Asia-Pacific region; however, they could provide a global improvement to PROD. The difference in PROD results between the Asia-Pacific region and the non-Asia-Pacific region is not apparent. Furthermore, the value of the Ambiguity Dilution Of Precision (ADOP), based on BDS + GPS, decreases by 7.50% and 8.26%, respectively, compared with BDS-only and GPS-only. Finally, if the relative position between satellites is only a few kilometres, the effect of ephemeris errors on PROD could be ignored. However, for a several-hundred-kilometre separation of the LEO satellites, the Single-Difference (SD) ephemeris errors of GEO satellites would be on the order of centimetres. The experimental results show that when IGSO satellites and Medium-Earth-Orbit (MEO) satellites co-work with GEO satellites, the accuracy decreases by 17.02%.