The use of small nuclear reactors for deep space or planetary missions presents some unique challenges regarding the operations and control of the power system. A SRPS can supply high-sustained power for space and surface applications that is both reliable and mass efficient. Additionally, application of SRPS modules as a planetary power source is being investigated to enable a continuous human presence for nonpolar lunar sites and on Mars. In recent years, the National Aeronautics and Space Administration (NASA) has been considering deep space missions that utilize a small-reactor power system (SRPS) to provide energy for propulsion and spacecraft power. The prospective architectural framework employs a hierarchical structure to integrate needed control, diagnostic, and decision functions and thus enable autonomy. 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 desirable characteristics of autonomous control include intelligence, robustness, optimization, flexibility, and adaptability. 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 SRPS control for an extended deep space mission. Thus, the development and demonstration of autonomous control capabilities for the specific domain of space nuclear power operations is needed. However, autonomous control is primarily intended to account for the non optimum circumstances when degradation, failure, and other off-normal events challenge the performance of the reactor and near-term human intervention is not possible. Current automated control technologies for nuclear power plants are reasonably mature, and basic control for a SRPS is clearly feasible under optimum circumstances. 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. It was found that control systems with varying levels of autonomy have been employed in robotic, transportation, spacecraft, and manufacturing applications. Oak Ridge National Laboratory (ORNL) has conducted an investigation of 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. Thus, a SRPS control system must provide for operational more ยป autonomy. In contrast, the control system of a space reactor power system (SRPS) 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. Terrestrial nuclear reactors employ varying degrees of human control and decision-making for operations and benefit from periodic human interaction for maintenance. The application of nuclear reactors for space power and/or propulsion presents some unique challenges regarding the operations and control of the power system.
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