Multi-phase-mission reliability of maintained systems

Abstract

In a phased mission the functional organization of the system changes at selected times which mark the boundaries of the phases of the mission. Existing methods for analysis of phased missions are modified and extended to permit determination of the reliability of maintained systems. Results are first obtained for the case when maintenance is performed only during a standby period, called the operational readiness phase, during which the system functions solely to maintain its readiness for a later period of active operations, as is the case for strategic weapons and safety devices. These results are then extended to systems which perform complex multi-objective missions to permit assessment of system performance at levels intermediate between total failure and total success. The reliability of systems which are maintained throughout a multi-phase mission is also considered. Two bounds on system reliability are developed--one based on the within-phase reliability of the system and the other on the phase minimal cut sets. Compatible lower bounds on the reliability of phase minimal cut (parallel) systems of independent components with exponential failure and repair times are considered.