Evaluation of strategies for the ultra-rapid orbit prediction of BDS GEO satellites

The quality of BeiDou Navigation Satellite System(BDS)Geostationary Earth Orbit(GEO)ultrarapid products is unsatisfactory because GEO satellites are nearly stationary relative to ground stations.To optimize the quality of these ultra-rapid orbit products,we investigated the effects of the fitting arc length,an a priori Solar-Radiation Pressure(SRP)model,and the along-track empirical acceleration on the prediction of BDS GEO satellite orbits.The predicted orbit arcs of 24-h were evaluated through comparisons with the corresponding observed orbit arc and Satellite Laser Ranging(SLR)observations.In both eclipse and non-eclipse seasons,accuracy of the orbit predictions obtained using a 48-h fitting arc length were better than those obtained using 24-h and 72-h fitting arc lengths.Although the overlapping precision of predicted orbits exhibited no obvious improvement when an a priori SRP model was employed,the systematic bias in the SLR residuals was significantly reduced.Specifically,the mean value of SLR residuals decreased from−0.248 m to−0.024 m during non-eclipse seasons and from−0.333 m to−0.041 m during eclipse seasons,respectively.In addition,when an empirical acceleration in the along-track direction was introduced,the three-Dimensional Root-Mean-Square(3D RMS)of overlapping orbits during eclipse seasons decreased from 2.964 to 1.080 m,which is comparable to that during non-eclipse seasons.Furthermore,the Standard Deviation(STD)of SLR residuals decreased from 0.419 to 0.221 m during eclipse seasons.The analysis of SRP estimates shows that the stability of SRP parameters was significantly enhanced after the introduction of along-track empirical acceleration in eclipse seasons.The optimal BDS GEO ultra-rapid orbit prediction products were yielded by using a 48-h fitting arc length,an a priori SRP model and an along-track empirical acceleration.