Military satellite communications (milsatcom) systems require precise timekeeping in order to take advantage of spread-spectrum communication techniques. Though the level of precise timekeeping in milsatcom is typically not as stringent as that in satellite navigation, mlsatcom nevertheless poses its own unique timekeeping problems. Specifically, milsatcom timekeeping muist be robust, with the ability to autonomously detect and correct timekeeping problems during protracted periods when the ground control station is either not available or burdened with other pressing tasks. Here, we consider the ability of three different space-segment timekeeping subsystems to autonomously detect the failure of a single satellite clock and to then take appropriate action to remedy the situation. these systems include a Master/Slave system, an Ensembling system, and a Kalman-Filter system. employing Monte Carlo simulation, we consider four types of "soft" clock failure: a time-jump failure, a frequency-jump failure, a failure arising from a sudden change in the clock's random-walk frequency noise. Our results demonstrate that the performance of the three space-segment timekeeping subsystems can be enhanced by adding general "clock failure rules" to the basic algorithms that are associated with each system. Once in place, these rules provide for robust, autonmous space-segment timekeeping, even in the presence of satellite clock failures.
展开▼
