高精度星间时差测量及补偿技术研究

Time difference measurement and compensation technique is one of fundamental techniques in satellite formation flying, which is one of the most popular techniques in aerospace field. This research will focus on the key techniques in high accuracy time difference measurement and compensation system, based on the micro-satellite formation flying, which has much restriction on its size and power consumption. On one hand, a method of time difference measurement appropriate for small satellite will be developed, aiming at improving the measurement accuracy with very limited resources in the micro-satellite missions; on the other hand, a compensation technique will be developed in digital form, to reduce the accuracy decay caused by environmental factors. However, the compensation accuracy is limited by the discrete characteristic of digital systems. A method called precisely phase shifting will be applied to solve this issue and to improve the compensation accuracy. Then, a close-loop feedback system will be built with both time difference measurement module and compensation module. The stability of this system will be ensured based on reducing the negative effect of the large time delay, by estimating the real-time time difference with the Kalman filtering technique. The target of this research is to build a time difference measurement and compensation system, which is appropriate for micro-satellite formation flying missions, both theoretically and methodologically. We expect this research can contribute to the development of micro-satellite formation flying techniques.

微小卫星编队飞行是当前国际航天界最为活跃的新技术领域之一，而星间时差测量与补偿技术是微小卫星编队的重要支撑技术。本项目以微小卫星编队应用为背景，对小型化、低功耗等约束条件下的高精度星间时差测量和时差补偿的关键技术进行研究。项目一方面从原理上探索出一种适用于微小卫星的高精度时差测量方法，在微小卫星平台资源有限的前提下提高星间时差测量的精度；另一方面针对时差补偿的数字实现，研究精确数字移相等技术，探索出解决时差补偿精度受限于数字实现问题的方法，提高星间时钟同步的水平；再针对时差测量与时差补偿形成的闭环负反馈系统存在的稳定性问题，应用Kalman滤波等技术，探索出一种时差预估技术以降低延时对环路的影响，提高环路的稳定性。通过项目研究，建立一套完整的适用于微小卫星编队应用的星间时差测量与补偿方案理论和实现方法，从而加快微小卫星编队技术发展的步伐。

本项目以微小卫星编队飞行应用为背景，对编队应用中的星间时差测量和星间时差补偿关键技术进行研究。通过理论、仿真和实验研究，项目取得的主要研究成果包括：（1）提出了基于非相干扩频伪码相位、双单程对发差分的星间时差测量方案，从而在不增加系统硬件资源消耗的前提下有效提高了星间时差测量性能。（2）提出了基于NCO的改进型时差补偿方案，利用dither算法和CP-PLL有效的提高了时差补偿的精度、减小了时差补偿后的相位抖动。（3）首次将星间时差测量系统与星间时差补偿系统进行整合，形成了实时闭环负反馈时差同步系统，大幅提高了时差同步的实时性，弥补了以往系统仅将时差信息进行后处理的缺陷。.研究成果表明项目目标已经实现，而且所达到的时差测量精度与补偿精度达到了目前同领域中的国际先进水平。本项目的研究成果不仅可应用于卫星编队领域，也可推广到其它需要对时差进行高精度同步的应用场合。