Reliability modelling and assessment of PMSs considering failure coupling effect between missions

Phased-mission systems (PMSs) consist of multiple sequential phases, where variations in system configurations, environmental conditions, and load levels across phases lead to complex failure coupling effects that challenge accurate reliability assessment. This paper proposes a reliability modelling and assessment framework for PMSs considering failure coupling effects between mission phases based on the Failure-Coupling-based Binary Decision Diagram (FC-BDD). The framework employs logical structure modeling rules to implement hierarchical modeling from the failure mechanism layer to the system layer and further to the mission phase layer, accurately capturing both intra-layer node relationships and inter-layer dependencies. In addition, analytical calculation rules for node associations are defined to enable quantitative reliability assessment of the system. Finally, the proposed method is applied to the ignition electronic control unit (PS-IECU) of a reusable deep-space propulsion system, demonstrating its effectiveness in reliability modeling and assessment. The study also reveals that neglecting coupling effects across mission phases can lead to cumulative errors in reliability assessment and hinder the identification and optimization of system-critical vulnerabilities.