Ultrahigh Specific Impulse Nuclear Thermal Propulsion

Abstract

PREFACEResearch on nuclear thermal propulsion systems (NTP) have been in forefront of the space nuclear power and propulsion due to their design simplicity and their promise for providing very high thrust at reasonably high specific impulse. During NERVA-ROVER program in late 1950's till early 1970's, the United Sates developed and ground tested about 18 NTP systems without ever deploying them into space. The NERVA-ROVER program included development and testing of NTP systems with very high thrust (~ 250,000 lb f ) and relatively high specific impulse (~ 850 s). High thrust to weight ratio in NTP systems is an indicator of high acceleration that could be achieved with these systems. The specific impulse in the lowest mass propellant, hydrogen, is a function of square root of absolute temperature in the NTP thrust chamber. Therefore, optimizing design performance of NTP systems would require achieving the highest possible hydrogen temperature at reasonably high thrust to weight ratio. High hydrogen exit temperature produces high specific impulse that is a direct measure of propellant usage efficiency.After the cancellation of the US NERVA-ROVER program in early 1970's, the Former Soviet Union continued with the US effort and made improvement in fuel design that enabled design and ground testing of an NTP systems (1984) at temperatures and specific impulses well above what had been achieved during the NERVA-ROVER program (hydrogen exit temperature ~ 3,000 K and specific impulse ~ 1,000 s). The renewed interest in the space nuclear power and propulsion is the main motivation for the proposed research that is intended to develop reactor design and NTP systems for achieving the highest possible specific impulseResearch conducted in support of the development of a new nuclear powered thermal rocket propulsion system is proposed to provide variable thrust in the range of 1,000 to 10,000 lb f of thrust at 1000-1500 seconds of ideal specific impulse (Isp) by heating relatively lowpressure hydrogen propellant to average temperatures ranging from 3000 K to 3250 K. The reactor for the proposed NTR concept is fueled with a uranium tetra-carbide compound that is optimized for resisting atomic and molecular hydrogen at temperatures above 3000 K. Uranium tetra-and tri-carbide fuels feature the highest corrosion resistance properties at elevated temperatures in hydrogen environment. The congruent melting of tetra-and tri-carbides is not overly sensitive to carbon content, as it's the case for uranium bi-carbides such as uraniumzirconium and uranium-niobium carbides. This is a key property of these fuels that would enable their applications for operation at temperatures above 3000 K. The fuel candidate for this concept is the solid solution of uranium-zirconium-niobium-titanium carbide, (U, Zr, Nb, Ti)C.Compare to uranium tri-carbides that have previously been considered for application in NTP systems, the proposed uranium tetra-carbide features higher stability in dissociated hydrogen and more favorable neutronic characteristics...

Synthesis and characterization of (Zr1/3Nb1/3Ti1/3)C metal carbide solid‐solution ceramic

“…In particular, MC solid‐solution ceramics have attracted considerable attention among these solid‐solution ceramics because of their extremely high melting points, high hardness, and high thermal and electric conductivity and are promising candidates for use in industrial, space, and armor applications . Until now, much effort has been devoted to the synthesis of the binary, ternary or quaternary MC solid‐solution ceramics. In particular, (U, Zr, Nb, Ti)C solid‐solution ceramics, as a member of MC solid‐solution ceramics, have attracted considerable attentions due to their extremely high‐temperature capability, high thermal and electric conductivity, low volatility, and good neutronic properties, which are promising candidates for use in nuclear industrial, space, and armor applications .…”