空间激光链路时频传递算法及仿真分析

Simulation Analysis of Time and Frequency Transfer Algorithm for Space Laser Link

利用空间高精度时频系统提供的超高精度时间频率信号,可以开展一系列空地时频传递和基础物理实验,支撑相对论及相关理论的高精度检验。针对空间激光链路时频传递算法进行了理论推导及仿真分析。首先,从星地激光双向时间比对理论公式出发,对比分析了X型星地双向时间比对与Lambda型星地双向时间比对的优缺点。其次,针对空间站轨道高度讨论了相对论效应对坐标时与原时转换的影响。最后,讨论了空地时频比对数据不连续性对空间站高精度原子钟稳定性评估的影响。结果表明:(1)基于激光测距方式的Lambda型双向时间比对可以抵消一阶多普勒对上下行距离项差异的影响,且Sagnac项影响的增大可忽略;(2)星地时间比对中坐标时和原时转换的相对论项对空间站位置的速度精度提出了高要求,为实现1×10-18量级的频率偏差比对精度,空间站地心距精度要求为1dm,速度精度要求为0.1 mm/s;(3)受空间站对地可见性影响,仅利用国内测站无法通过星地链路进行中短期原子钟稳定性的评估。

Objectives:With the ultra-high precision time and frequency signals provided by space high pre-cision time and frequency system,series of space-to-ground time and frequency transfer and fundamental physics experiments can be carried out to support high precision validation of relativity and related theories.Methods:First,theoretical derivation and simulation analysis are conducted on the time and frequency transfer algorithm of space laser links.Theoretical formula of space-to-ground laser two way time transfer are reviewed,and the advantages and disadvantages of X-type and Lambda-type approaches are compared and analyzed.Then,the impact of relativistic effects on the conversion between proper time and coordinate time is discussed for the specific orbital height of China space station.Finally,the impact of space-to-ground time and frequency transfer discontinuity on the stability evaluation of high-precision atomic clocks onboard space stations is discussed.Results:The results show that:(1)Lambda-type two-way time trans-fer based on satellite laser ranging can make up the distance difference of first-order Doppler effect on the uplink and downlink,and increase of Sagnac effect can be ignored.(2)The relativistic effect of the conversion between proper time and coordinate time for satellite ground time transfer makes high demands on the velocity accuracy of space station positions,in order to achieve 1X10-18 frequency transfer accuracy,geocentric distance accuracy of 1 dm and speed accuracy of 0.1 mm/s of space station is required;(3)Influenced by the visibility of space stations to the ground,it is not possible to evaluate the medium term stability of atomic clocks with only the observation data of domestic stations satellite for space-to-ground links.Conclusions:High precision navigation solution is important to ensure high-precision time and frequency transfer between space and ground.How to optimize navigation algorithms and use various payloads onboard to achieve high-precision position and velocity solution is a key issue that needs to be studied.