Precise Time Synchronization of Two Milstar Communications Satellites WithoutGround Intervention

摘要

Satellite navigation and communication systems often require precisesynchronization among spacecraft clocks. In the traditional method for achieving synchronization, a ground station makes time-offset measurements to the various spacecraft clocks, and then updates the time and frequency of each satellite as needed. Though straightforward in its implementation, disadvantages to the traditional approach include the large workload placed on the ground station, the need for multiple ground stations to view satellites in different geosynchronous positions, and unaccounted-for delays in atmospheric propagation. In early 1996, Milstar became the first satellite system to employ crosslinks for precise satellite time synchronization. At that time, the crystal oscillator clock onboard FLT-1, the first Milstar satellite, had its time and frequency tied (i.e., slaved) to the rubidium (Rb) atomic clock carried onboard FLT-2, the second Milstar satellite. The FLT-2 Rb atomic clock was controlled by the ground, while the slaving of FLT-l to FLT-2 was accomplished without ground intervention: all timing information required by the slaving algorithm was obtained through the