Nuclear Electric Propulsion for Deep-Space Missions: Technologies, Challenges, and Future Outlook

Nuclear electric propulsion (NEP) is increasingly recognized as a cornerstone technology for future deep-space missions, offering solutions to the performance limits of conventional chemical propulsion. This review consolidates recent progress in NEP system architectures, with particular focus on compact fission reactors, high-efficiency power conversion units, and advanced electric thrusters, such as ion engines, Hall-effect devices, and magnetoplasmadynamic systems. The technological trajectory is traced from early demonstrations, including SNAP-10A and the Soviet TOPAZ reactors, to current initiatives such as the U.S. National Aeronautics and Space Administration’s kilopower and DRACO projects, the European Space Agency’s Future Launchers Preparatory Programme, and Roscosmos’s Transport and Energy Module.Critical challenges, ranging from reactor miniaturization and thermal management at high operating temperatures to radiation protection and regulatory approval, are examined alongside emerging solutions such as artificial intelligence–assisted autonomy, digital-twin modeling, and metamaterial radiator concepts for megawatt-class platforms.To structure this landscape, we introduce a mission taxonomy based on reactor output [ 100 kW(electric)] and provide new analyses of radiator mass scaling as well as comparative performance of NEP and alternative propulsion systems for Mars logistics. Looking forward, pathways include modular reactor arrays, hybrid propulsion architectures combining NEP with solar-electric or chemical systems, and the establishment of coordinated international policy frameworks. Together, these elements outline a roadmap for advancing NEP from experimental demonstrations to operational systems, reinforcing its role as a foundation for sustainable interplanetary exploration.