Identifying the major contributions to risk in phased missions

Many systems operate phased missions. The mission consists of a number of consecutive phases where the functional requirement of the system changes during each phase. A successful mission is the completion of each of the consecutive phases. For non-repairable systems, efficient analysis methods have recently been developed to predict the mission unreliability. In the event that the predicted performance falls below that which is required, modifications are made to improve the design. In conventional system failure analysis importance measures, which identify the contribution each component makes to the failure, can be used to identify the weaknesses. Importance measures relevant for phased mission applications are developed in this paper.