Systems reliability for phased missions

The concept of a phased mission has been introduced as a sequential set of objectives that operate over different time intervals. During each phase of the mission, the system may alter such that the logic model, system configuration, or system failure characteristics may change to accomplish a required objective. A new fault tree method has been proposed to enable the probability of failure in each phase to be determined in addition to the whole mission unreliability. Phase changes are assumed to be instantaneous, and component failure rates are assumed to be constant through the mission. For any phase, the method combines the causes of success of previous phases with the causes of failure for the phase being considered to allow both qualitative and quantitative analysis of both phase and mission failure. A new set of Boolean laws is introduced to combine component success and failure events through multiple phases so that the expression for each phase failure can be reduced into minimal form. [Continues.]