利用不同时间同步体制钟差评估北斗三号星载原子钟性能

Performance Evaluation of BDS-3 Spaceborne Atomic Clock Using Different Time Synchronization Systems

全球卫星导航系统(global navigation satellite system,GNSS)星载原子钟性能的优劣直接影响GNSS观测信号质量、测距精度、钟差预报与卫星自主导航能力,从而间接影响整个导航系统的服务性能。结合北斗三号系统独特的星间链路(inter-satellite link,ISL)和星地时间双向比对(two-way time transfer,TWTT)体制以及常用的精密轨道与钟差确定(orbit determination and time synchronization,ODTS)体制所估计的精密钟差数据,分析评估了北斗三号在轨原子钟服务性能。结果表明,3种钟差确定体制评估的频率准确度和漂移率结果基本一致,所有卫星频率准确度在(-4~2)×10^(-11)范围以内,氢钟频率准确度优于铷钟,ISL钟差评估的频率漂移率精度略优于ODTS。在评估原子钟稳定度方面,3种钟差确定体制各有优势,短期稳定度方面,ODTS钟差评估优于ISL钟差,基于ODTS评估的3000 s稳定度可达3×10^(-14),且氢钟的短期稳定性优于铷钟;中长期稳定度方面,当平滑时间大于1×10^(4)s时,采用ISL体制的钟差评价中长期稳定度更接近于北斗三号星载原子钟的实际情况;对于7 d以上的长期稳定度评估,基于TWTT的广播钟差评估结果接近于ISL,可用于快速评估。

Objectives The performance of the global navigation satellite system(GNSS)spaceborne atomic clock affects the entire navigation system,by having direct impact on GNSS measurement quality,ranging precision,clock prediction and satellite autonomous navigation capabilities.Different time synchronization systems may have different impact on the evaluation of spaceborne atomic clock.Precise clock bias data determined by inter-satellite link(ISL),two-way time transfer(TWTT)and orbit determination and time synchronization(ODTS)system are used to further evaluate the performance of BeiDou-3 on-orbit atomic clock.Methods Quadratic polynomial model and total Allan/Hadamard variance are used to analyze the performance of the BeiDou-3 navigation satellite system(BDS-3)satellite clock data of the three different time synchronization systems.Results The result shows that the frequency accuracy and frequency drift of the above three clock bias determination systems are consistent.The frequency accuracy of all satellites is within the range of(-4~2)×10^(-11).Frequency accuracy of hydrogen clock is better than that of rubidium clock.The frequency drift based on the ISL system is slightly better than that of the ODTS,the three clock determination systems have their own advantages in evaluating the stability of the atomic clock,respectively.For short-term stability,the ODTS whose 3000 s stability reaches 3×10^(-14) is better than that of ISL,and hydrogen clock is better than rubidium clock.For medium-term and long-term stability,when the averaging time is greater than 1×10^(4) s,the result of ISL is closer to the actual condition of the BDS-3 spaceborne clock.For long-term stability more than 7 days,the broadcast ephemeris bias based on TWTT system can be used for rapid evaluation,which result is close to ODTS and ISL.Conclusions The three clock bias determination systems can be used to evaluate the frequency accuracy and frequency drift of on-orbit atomic clocks with basically consistent statistical results.The three clock bias determination systems have their own advantages in assessing the stability of the orbiting satellite clock when selecting different averaging time.