The use of dynamics in an intelligent controller for a space faring rescue robot

Abstract The NASA Extra Vehicular Activity Retriever (EVAR) robot is being designed to retrieve astronauts or objects that become detached from the orbiting Space Station. This task requires that the robot's intelligent controller must rely heavily on orbital dynamics predictions, without becoming blind to the wide variety of anomalies that may occur. This article describes the controller's Universal Plan (U.P.) and some technical lessons learned from it. The U.P. reacts not to actual current states but to estimated states, which are obtained using goal-directed active perception. A modal logic formalization of discrete-event dynamics allows us to finely analyze and specify the interactions of knowledge, belief, sensing, acting, and time within the U.P. The U.P. now acts like a hands-off manager: it makes regular observations, grants some leeway for unobservable or ill-modelled processes, has faith in subsystem dynamics, and takes action only to manipulate subsystems into delivering desired progress. Most of the time, the appropriate action is to do nothing. Finally we examine properties of the application that allowed the U.P. to deliver robust goal achievement despite misleading state estimates, weak models of relevant processes, and unpredictable disturbances.