Multidisciplinary Analysis of Nuclear Thermal Propulsion Design Options for Human Exploration Missions

Abstract

The purpose of this paper is to discuss the results of mission-based system trades when using a nuclear thermal propulsion (NTP) system for Solar System exploration. The results are based on comparing reactor designs that use a ceramic-metallic (CERMET), graphite matrix, graphite composite matrix, or carbide matrix fuel element designs. The composite graphite matrix and CERMET designs have been examined for providing power as well as propulsion. Approaches to the design of the NTP to be discussed will include an examination of graphite, composite, carbide, and CERMET core designs and the attributes of each in regards to performance and power generation capability. The focus is on NTP approaches based on tested fuel materials within a prismatic fuel form per the Argonne National Laboratory testing and the ROVER/NERVA program. NTP concepts have been examined for several years at Pratt & Whitney Rocketdyne for use as the primary propulsion for human missions beyond earth. Recently, an approach was taken to examine the design trades between specific NTP concepts; NERVA-based (UC)C-Graphite, (UC,ZrC)CComposite, (U,Zr)C-Solid Carbide and UO 2-W CERMET. Trade studies to examine the design attributes have been performed with some detailed conceptual design and engineering analysis that has included mechanical design, heat transfer, neutronics, thermodynamics, and thermo-hydraulics. Engineering analysis and modeling of the reactor criticality, mass properties, propulsion mode mass and thermodynamic cycle (and power mode thermodynamic cycle for the (UC,ZrC)C-Composite and CERMET) have been performed recently. Using Pratt & Whitney Rocketdyne’s multidisciplinary design analysis capability, a detailed mission and vehicle model has been used to examine how several of these NTP designs impact a human Mars mission. Trends for the propulsion system mass as a function of power level (i.e. thrust size) for the graphite-carbide and CERMET designs were established and correlated against data created over the past forty years. These were used for the mission trade study. The ultimate goal before designing a NTP for human missions would be to select a fuel-type that is robust enough for propulsion and power that can be formulated into a reduced-risk reactor design and propulsion system.