SBDD-based reliability evaluation method for redundant phased mission systems

This paper addresses the reliability evaluation of a specific category of Phased Mission Systems (PMS), referred to as Redundant PMS. In these systems, certain components function as shared redundant resources that are competitively allocated to multiple mission phases according to the First-Failure-First-Occupied (FFFO) principle. This shared redundancy approach enhances system reliability and improves resource utilization efficiency. However, the competition for shared resources introduces considerable complexity in analyzing the system’s failure logic, necessitating explicit consideration of inter-phase failure sequences. To overcome this challenge, a quantitative evaluation methodology based on Dynamic Fault Trees (DFT) and Sequential Binary Decision Diagrams (SBDD) is proposed. The DFT framework accurately models the FFFO competition logic governing the occupation of shared redundant resources across phases. The SBDD technique effectively addresses the high structural coupling characteristic of DFT models for redundant PMS. Notably, this research optimizes SBDD construction, including variable ordering and phase-dependent operations, specifically for the multi-phase context. Furthermore, it innovatively applies Hasse diagrams combined with a topological sorting algorithm to decompose SBDD paths with partial-order failure sequences into mutually exclusive Cut Sequence Sets (CSS), thereby enabling quantitative reliability analysis. A case study validates the effectiveness of the proposed method in quantifying the reliability of complex PMS, providing a precise reliability foundation for system design and optimization.