Investigation of Autonomous Control for the Jupiter Icy Moons Orbiter

The application of nuclear reactors for space power and/or propulsion presents some unique challenges regarding the operations and control of the power system. Terrestrial nuclear reactors employ varying degrees of human control and decision-making for operations and benefit from periodic human interaction for maintenance. In contrast, the control system of a space nuclear power plant (SNPP) employed for deep space missions must be able to accommodate unattended operations due to communications delays and periods of planetary occlusion while adapting to evolving or degraded conditions with no opportunity for repair or refurbishment. Thus, a SNPP control system must provide for operational autonomy. To support the Jupiter Icy Moons Orbiter (JIMO) project, Oak Ridge National Laboratory investigated the state of the technology for autonomous control to determine the experience base in the nuclear power application domain, both for space and terrestrial use. It was found that control systems with varying levels of autonomy have been employed in robotic, transportation, spacecraft, and manufacturing applications. However, autonomous control has not been implemented for an operating terrestrial nuclear power plant nor has there been any experience beyond automating simple control loops for space reactors. Current automated control technologies for nuclear power plants are reasonably mature and basic control for a SNPP is clearly feasible under optimum circumstances. However, autonomous control is primarily intended to account for the nonoptimum circumstances when degradation, failure, and other off-normal events challenge the performance of the reactor and near-term human intervention is not possible. Thus, the development and demonstration of autonomous control capabilities for the specific domain of space nuclear power operations is needed. This paper will discuss the findings of the ORNL study and provide a description of the concept of autonomy, its key characteristics, and a prospective functional architecture that can support SNPP control for an extended deep space mission. The desirable characteristics of autonomous control include intelligence, robustness, optimization, flexibility, and adaptability. The degree of autonomy that is necessary for a given mission will depend on resource constraints, performance goals, operational complexity, technological capabilities, and mission risk considerations. The prospective architectural framework employs a hierarchical structure to integrate needed control, diagnostic, and decision functions and thus enable autonomy.