The real-time orbit determination(RTOD)performance with onboard BDS-3 and GPS observations from a Chinese low Earth orbit satellite,LT-01A,is analyzed,with a focus on the impact of broadcast ephemeris rotation error on RTOD accuracy.The orbit rotation errors of GPS and BDS-3 broadcast ephemeris are evaluated by Helmert transformation with respect to post pre-cise orbit product.BDS-3 broadcast ephemeris reveals rotation errors reaching up to-8.7 mas,and indicates an average rotation error about 2.5 times larger than that of GPS.After the rotation correction of BDS-3 broadcast ephemeris,the root mean square(RMS)errors in the along-track and cross-track components of BDS-3 broadcast ephemeris show significant reductions from about 25 cm to a level around 10 cm,manifesting an improvement by more than 50％.Therefore,the RTOD accuracy based on spaceborne BDS-3 and BDS-3/GPS combination are significantly affected by the rotation error of BDS-3 ephemeris,which mainly degrades the along-track and cross-track components.For BDS-3 only RTOD,the along-track,cross-track,and radial RMS errors with ro-tation correction are 21.0 cm,10.7 cm,and 11.2 cm,respectively;the along-track and cross-track accuracies present improvements by 15.0％and 31.8％,respectively.By combining BDS-3 and GPS observations,the RTOD errors at the along-track components are further improved to 19.4 cm.Thanks to the high accuracy of BDS-3 broadcast ephemeris,the three-dimensional RMS errors of independent BDS-3 and combined BDS-3/GPS RTOD are 31.9 cm and 29.2 cm,respec-tively,which are 9.1％and 16.8％smaller than GPS-only RTOD errors,respectively.With rota-tion correction,the orbit determination accuracies are improved to 26.7cm and 25.0cm,respec-tively,which is 22.6％and 27.5％smaller than those of single GPS real-time orbit determination.
Low Earth orbit satelliteBeiDou navigation satellite system with global coverage(BDS-3)Broadcast ephemerisReal-time orbit determinationRotation error
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