Comparing Run Time Assurance Approaches for Safe Spacecraft Docking

Run Time Assurance (RTA) systems are online safety verification techniques that filter the output of a primary controller to assure safety. RTA approaches are used in safety-critical control to intervene when a performance-driven primary controller would cause the system to violate safety constraints. This paper presents four categories of RTA approaches based on their membership to explicit or implicit monitoring and switching or optimization interventions. To validate the feasibility of each approach and compare computation time, four RTAs are defined for a three-dimensional spacecraft docking example with safety constraints on velocity.