Algorithm of intersatellite dynamic two-way time transfer based on GEO satellite

Two-way time transfer is a common method applied to spacecrafts and ground stations to carry out time transfer. This method improved the accuracy of time transfer by eliminating the impact of propagation paths and extra delay caused by atmosphere, so the algorithm of two-way satellite time transfer is presently one of the time transfer methods with high accuracy. But this method requires the spacecrafts and ground stations, on which time transfer is to be performed, to keep a relatively static state in time transfer. So it is mainly used in GEO satellites for satellite-ground two-way time transfer. On the basis of two-way satellite time transfer algorithm, the characteristics of the propagation delay of two-way time transfer signals between MEO satellite and GEO satellite varying with intersatellite range were analyzed, and the rule of intersatellite clock offset varying with intersatellite range obtained with this algorithm was deduced. This paper presents a dynamic two-way time transfer algorithm(DTWTTA) with which high-accuracy intersatellite clock offset is solved through the combination of intersatellite pseudo-range polynomial fitting and clock-offset polynomial fitting. Simulation data of actual satellites showed that with the algorithm the intersatellite time transfer error can be controlled within 5ns provided with minimum square fitting, the two-way time transfer periods beginning at moments basically symmetrical with the occurrence of minimum intersatellite range relatively, and the impact of other factors being taken into account. As a result the algorithm can be used for intersatellite high-accuracy time transfer.