Abstract: A nuclear thermal rocket engine is provided with an integrated and compact construction that facilitates vehicle size and weight reduction. The engine includes a nuclear reactor core having multiple fuel assemblies and moderator rods disposed therebetween. A reactor vessel surrounds a reflector assembly which surrounds the core and includes multiple passages formed therein for circulating coolant therethrough. The reactor vessel is surrounded by a nozzle assembly which includes a nozzle block having a plenum fluidly coupled to the outlets of the fuel assemblies and a nozzle throat region. Multiple struts extend from the reactor vessel and through the nozzle throat region to divide that region into multiple nozzle throats. Each strut includes multiple channels for circulating coolant (e.g.

Abstract: A nuclear propulsion reactor. A reactor vessel is provided with an annular first core and a cylindrical second core that is radially encompassed by the first core. Nuclear fuel elements in the first core provide first stage heating of propellant as they direct the propellant axially through the first core. The second core, which contains fissionable material in a highly refractory form, is in fluid communication with the first core for receiving the heated propellant. Fission reactions in the second core driven by leakage neutrons from the first core provide second stage heating of the propellant as it passes therethrough. The second core directs the coolant to a propellant nozzle for providing propulsive thrust.

Abstract: High temperature reactor with residual-heat transfer system comprises a cooling gas intake at the bottom and cooling gas outlet at the top so that a cooling gas can flow from the bottom to the top through the reactor core. In order to assure reliable heat transfer a bypass duct is provided with a lower end communicating with the cooling gas intake and the upper end communicating with the cooling gas outlet. The bypass duct is arranged parallel to the reactor core and passing a partial flow of cooling gas from the bottom to the top. This partial flow of cooling gas heats up only trivially. This partial flow of cooling gas is further cooled by the cooler. The upward flow of the comparatively cold cooling gas in the bypass duct stops and by itself reverses because the cooling gas in the bypass duct is drawn toward the reactor core on account of the natural convection.