Small Nuclear Rocket Engine and Stage Benchmark Model

摘要

Advancement of U.S. scientific, security, and economic interests through a robust space exploration program requires high performance propulsion systems to support a variety of robotic and crewed missions beyond low Earth orbit. Past studies, in particular those in support of both the Strategic Defense Initiative (SDI) and Space Exploration Initiative (SEI), have shown nuclear thermal propulsion systems provide superior performance for high mass high propulsive delta-V missions. An extensive nuclear thermal rocket technology development effort was conducted from 1955-1973 under the Rover/NERVA Program. The Small Nuclear Rocket Engine (SNRE) was the last engine design studied by the Los Alamos National Laboratory during the program. At the time, this engine was a state-of-the-art design incorporating lessons learned from the very successful technology development program. Past activities at the NASA Glenn Research Center have included upgrading and modernizing nuclear thermal propulsion system models and analysis methods. The SNRE had been adopted to serve as a computational benchmark for these activities. A highly detailed MCNP Monte Carlo transport model of the reactor core was developed and exercised along with a number of simpler MCNP models of the reactor core. The reactor core models, calculated results, and comparisons with available documentation for the SNRE were described in a previous (2007) Joint Propulsion Conference paper. The SNRE was originally intended for unmanned applications with relatively short engine operations and the engine and stage design were constrained to fit within the payload volume of the then planned space shuttle. Recent activities at Glenn Research Center have included development of MCNP models of the SNRE Reference Stage. The stage models include the liquid hydrogen propellant tank and simple representations of selected stage hardware components such as the turbopump assembly and propellant flow control valves. Results comparisons include energy deposition in the hydrogen propellant, neutron and gamma heating rates at selected external component locations, and instantaneous neutron and gamma dose rates at the tank top payload location as a function of hydrogen propellant level. Total neutron and total gamma doses at the tank top obtained by integrating the instantaneous dose rates as propellant is expended are also compared.