Research On Time Synchronization Technology In Spaceflight TT&C Network

The distributed Space TT&C Network adopts official NTP (Network Time Protocol) time server and builds time server as primary time reference for time synchronization. A global Space TT&C Network is Constructed by means of the existed civil Internet so as to transmit the measurement and control information of spacecraft. On the basis of these, the coverage of Space TT&C Network is improved in large range and further perfects the centralized Space TT&C Network. However, the accuracy of NTP is only several dozens milliseconds in Internet, comparing with the modern Space TT&C system, the difference of accuracy is significant.Thereby, establishment of network time synchronization system on the basis of NTP is a reasonable choice to solve those problems at present.The paper mainly focuses on improvement of the time synchronization accuracy and reliability of the distributed space TT&C network.Firstly, the paper adopts NTP as network synchronization protocol after analyzing advantage and disadvantage among several existent correcting time protocols in Internet. The range of network error can be further reduced after calculating and discussing, at the same time the paper improves the accuracy of time synchronization. The correctness of result is proved through the test in network environment.Secondly, two synchronization schemes are designed for distributed space TT&C network, and the system not only has a stronger adaptive capacity to the network environment, but also can achieve high accuracy and stability of the time synchronization even without external time server.Finally, time server selection algorithm is designed and applied before normal time synchronization. It makes the network adapt to the changes in the network environment, thereby the system can choose the best time server real-timely for time synchronization. Server selection algorithm is implemented on client. Comparing the experimental data from time server selection algorithms shows that application of the algorithms can not only obviously improve the precision of time synchronization in space TT&C network system, but also maintain the stable accuracy for long time.