SC-45(2) - System Time Synchronization | Secondary Authoritative Time Source

(a) Identify a secondary authoritative time source that is in a different geographic region than the primary authoritative time source; and (b) Synchronize the internal system clocks to the secondary authoritative time source if the primary authoritative time source is unavailable.


ID: SC-45(2)
Enhancement of : SC-45

Space Segment Guidance

A secondary authoritative time source for a spacecraft (e.g., a secondary GPS receiver, ground-station-provided time reference, or a stable onboard atomic clock) ensures continued accurate timekeeping if the primary reference degrades, is jammed, or experiences malfunction. In space systems, precise time synchronization is crucial for cryptographic key rotations, correctly ordering telemetry, and coordinating multi-satellite constellations. Having two independent time feeds also allows cross-checking for anomalies or adversarial tampering—for example, if a malicious party attempted to skew the primary time feed to invalidate secure sessions. Implementing rigorous fault-detection logic that automatically transitions to the secondary source (or raises the alarm) allows operators to maintain mission continuity and limit cascading failures in commanding and data handling. Even if the spacecraft’s primary clock remains healthy, a robust secondary source provides resiliency to mission timelines.