China's COMPASS satellite navigation system relies on a regional tracking network to provide navigation services. Limited by its geographic border,the regional network is able to cover only 30% of the medium-earth-orbits(MEO). Accuracy of determined and predicted orbits is not able to satisfy system requirements if the tracking data processing strategy for global tracking network processing is used for the regional network. Two major error sources for orbital prediction are accuracy of initial orbital elements and dynamical modeling. To achieve better prediction accuracy,we propose a two-step orbit determination and prediction strategy. For step 1,only solar radiation pressure(SRP) parameters are estimated along with the orbital elements and other parameters; for step 2,all parameters are estimated but the SRP parameters are tightly constrained to their step 1 estimates. Experimenting with data from a regional GPS network,we conclude for orbital prediction using the proposed two-step strategy,the average user range error(URE) for 24-h prediction arcs is better than 0.6 m.
ZHOU ShanShi 1,2,3 ,HU XiaoGong 1 & WU Bin 1 1 Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030,China
我国导航系统采用区域监测网提供轨道预报等导航服务.由于区域网不能覆盖地球中轨轨道(Medium Earth Orbit,MEO)卫星全弧段,并且受卫星相对于监测网几何条件限制,若采用与全球网相同的定轨和预报策略,预报精度难以满足我国导航系统的指标要求.预报精度决定于定轨获得的初轨和力学模型的精度.针对MEO卫星星座的区域监测网定轨预报问题,本文提出两步法策略,即首先解算部分动力学参数和轨道参数,然后强约束这部分动力学参数的估值,重新解算所有动力学参数和轨道,并利用得到的初轨和动力学参数进行轨道预报.利用实测GPS数据的实验表明,采用两步法定轨策略可获得对动力学参数的合理解算结果,并可提高轨道预报精度,预报1天轨道的平均用户距离精度(User Range Error,URE)优于0.6m.
