Modeling and evaluating an empirical INS difference monitoring procedure used to sequence SSBN navaid fixes

Ballistic missile equipped, nuclear powered submarines, denoted as Ships Submersible Ballistic Nuclear (SSBN), have to take navigation fixes in connection with a deterioration in the navigation accuracy provided by their Inertial Navigation System (INS). Such a degradation is related to gyro drift-rate and other sources. An SSBN utilization of the available possibilities for taking the navigation fixes involves an exposure to enemy surveillance. 'Difference Monitoring' is used to both randomize and extend the time between fixes, thus avoiding periodic patterns of fixes and reducing exposure to enemy surveillance. The Difference Monitoring procedure involves a computation of the radial position divergence concerning the outputs of two warm-standby INSs and a comparison of this statistic to a fixed design threshold. The present investigation provides a theoretical model for the previous empirical procedure of Difference Monitoring.