Liquid/Gas Core Reactors for High Acceleration Propulsion

Liquid and gaseous core nuclear engines aim at higher specific impulse by removing the melting point limit on solid fuel elements. The problem of separation of fuel and propellant then becomes the major criterion for feasibility of these advanced engine concepts. Proposals to achieve separation by centrifugal forces, regeneratively cooled partitions, and fluid dynamic flows are reviewed. Of these systems, fluidized beds are closest to assured feasibility but offer the smallest performance increase over solid core systems. Liquid core concepts offer significant difficulty with modest performance gains while gaseous core systems indicate substantial improvements in performance along with serious questions of feasibility. Conceptual approaches to separation problems in gaseous core reactors are reviewed along with problems of energy transfer between fuel and propellant as well as reactor criticality. Establishment of feasibility of any one concept will require significantly better understanding of the interaction among the fuel retention mechanism, radiant energy transfer, and criticality characteristics.