X射线脉冲星导航中钟差的可观测性问题

The Observability of Clock Error in Orbit Determination Using X-Ray Pulsar Based Navigation

标准X射线脉冲星导航(XNAV)能够求解航天器的位置信息,但航天器钟差会导致XNAV的结果产生误差。鉴于脉冲星周期的稳定性,在利用XNAV进行轨道估计中,将钟差作为状态变量进行估计的授时方案已被相关学者提出。一种针对卫星轨道修正专门设计的可观测性分析工具在文中给出,利用其能够有效地判断各个状态的可观测性情况。利用该方法分析将钟差作为状态变量的导航方案,其结果表明仅需2颗脉冲星就可以对全部轨道六根数,以及卫星钟差进行观测;仿真结果验证了可观测性分析结论,双脉冲星导航时系统可以达到60m的定位精度和60ns的授时精度。对比仿真同时揭示了该方案能够有效地抑制钟差对导航精度的影响,将由于钟差引起的定位误差减小20倍以上。理论分析与仿真表明,将钟差作为状态变量的导航方案是一种能够有效地估计钟差,并抑制钟差影响、提升系统估计精度的导航方案。

Standard X-ray pulsar based navigation（XNAV） can provide spacecrafts with autonomous positioning services,but the clock error of spacecraft will cause an approximate static measurement error in XNAV.In the light of the stability of pulsar＇s period,a new clock error estimation method taking the clock error as an extended state in orbit determination using XNAV is proposed by fellow researchers.An observability analysis tool specifically designed for the obit determination is given.The observability analysis based on this extended state method is conducted,and the results indicate that only 2 pulsars are required for the total observability of all the 6 orbit element errors and clock error.The simulation results confirm the observability analysis results： when 2 pulsars are used in XNAV a positioning accuracy of 60m and a timing accuracy of 60ns can be acquied.Comparison simulations also show this method can effectively suppress the effect of clock error on navigation accuracy,thus decreasing the positioning error caused by clock error by over 20 times.The analysis and simulations prove that the extended state method can estimate clock error along with orbit element errors,effectively suppress the clock error＇s effect and improve the navigation accuracy.