A framework to assess the operational state of autonomous ships with multi-component degrading systems

Ensuring that the safety level of autonomous ships is at least equivalent to the expected level of conventionally operated ships is a prerequisite for their smooth introduction into practical operation. Once the autonomous ship deviates from its operational envelope, it will enter a predetermined fallback state and easily lead to accidents. The response mechanism governing the operational state transitions of safety-centric autonomous ships is generally underexplored. This paper aims to develop a novel framework for assessing the operational state of autonomous ships with multi-component degrading systems and predicting the time threshold necessary for effective response actions. Its novelties consist of (1) a novel model to analyze and quantify the operational state of system considering degraded components; (2) an extension of system state assumption from a binary “normal-failure” to multi-state; (3) the utilization of System-Theoretic Process Analysis method to generate a functional control structure facilitating multi-state system modeling; and (4) elucidation of the transition mechanism applicable to the operational state of autonomous ships. The results indicate that the operational state of hardware facilities is less stable than software subsystems under ongoing routine maintenance, and the remotely-controlled ship with crew onboard may deviate from its operational envelope after 189.8 days without implementing any maintenance strategies. • Proposing a novel framework to assess operational state from the perspective of system safety. • An extension of system state assumption from a binary "normal-failure" to multi-state. • Elucidation of the transition mechanism applicable to the operational state of autonomous ships. • Theoretical support for preventing autonomous ships from deviating from the operational envelope was provided.