Ranging and sychronization between nominally co-orbital satellites

A link between two satellites can provide direct measurements of clock synchronism and intersatellite range that are more accurate than estimates obtainable from ground measurements. Moreover these direct measurements can be made continuously with near-zero delays. Two approaches to ranging and synchronization between satellite pairs are 'balanced' systems in which each satellite makes a time-difference measurement, and 'full loop' systems in which a time-difference measurement is made on only one satellite. This report discusses factors which determine the ultimate limitations and capabilities of both approaches, and compares the schemes for applications in which two digital clocks are actually brought into synchronism with accuracies of several nanoseconds.