Demonstration of Synchronization Between Two Geosynchronous Satellites Without Ground Intervention

摘要

In early 1996 Milstar became the first geosynchronous satellite system to employ crosslinks for synchronization and syntonization. At that time, the crystal oscillator onboard DFS-1, the first Milstar satellite, had its time and frequency tied (i.e., slaved) to the rubidium (Rb) atomic clock carried onboard DFS-2, the second Milstar satellite. The slaving of DFS-1 to DFS-2 was accomplished without ground intervention. All timing information required by the slaving algorithm was obtained through the DFS-1 to DFS-2 satellite crosslink. In this paper we discuss the drift and Allan variance of the two satellite clocks when operating independently, and show that both clocks are performing well. Additionally, we present ground station measurements of DFS-1 and DFS-2 time offsets that demonstrate satellite synchronization to better than 150 ns without ground intervention.