Safety Assessment of Maritime Autonomous Surface Ships: A Scenario-Based Approach

Kurzfassung

Maritime Autonomous Surface Ships (MASS) promise enhanced efficiency in shipping operations, but ensuring their safety presents significant challenges. Traditional distance-based testing, where safety is assumed after travelling a predetermined distance without incident, is impractical for MASS due to prohibitively large distance requirements. Drawing inspiration from the automotive domain, we apply scenario-based testing, where the space of operating conditions is divided into traffic scenarios. Scenario-based testing makes it possible to increase the efficiency of testing by specifically targeting high-risk scenarios. We employ maritime Traffic Sequence Charts (mTSCs) to formally specify test scenarios and corresponding requirements. Our approach encompasses three key elements. First, in a hazard analysis, risk-triggering scenario properties are systematically identified through expert-guided brainstorming and investigation of causal relationship. This results in abstract test cases and safety requirements, which are formally specified as mTSCs. In a second step, concrete test scenarios are generated for each abstract test case by converting mTSCs into mathematical SMT problems and solving these for vessel movements modelled as Bézier splines. Finally, runtime monitors derived from mTSCs are used to continuously evaluate requirement satisfaction during testing. We find that systematic hazard analysis, automated scenario generation, and runtime monitoring can successfully be applied to the verification of maritime systems. The formal specification enables automatic test execution and evaluation in both simulation and real-world environments.