*Nuclear Thermal Propulsion DOI: http://dx.doi.org/10.5772/intechopen.103895*

Application (NERVA) program under Werner von Braun, and was planned to enable a mission to Mars, launching in the early 1980s. NERVA ended after funding cuts at the end of the Cold War and the corresponding reduction of the scope of the space program. However, this work was resurrected in the mid 2010s as part of NASA's Game Changing Technology for Deep Space Exploration Program. Much of the experience gained under NERVA was used as a basis for a path forward.

Under NERVA, fuel forms were primarily composed of graphite fuel compacts, although independent work at ANL and GE began developing CERMET fuels. Recent efforts picked up CERMET fuel development, building on the earlier work in addition to other research related to application in other reactor types. NASA also began the evaluation of CERCER fuel forms; all current development efforts are based on the use of HALEU fuel instead of the HEU fuel used within the NERVA program. Tests of fabrication processes and high temperature operation in reactor and non-reactor facilities are underway.

By using the Griffin reactor multiphysics application coupled with the RELAP-7 thermal-fluids systems code and the MOOSE framework, tightly coupled multiphysics simulations are being performed for CERMET-based core designs. The simulation of experiments being performed at the TREAT facility is also underway to aid in the experimental design. Data from the completed experiments are being used to validate the coupled approach.

Much work remains to be completed, both in core design analysis and materials testing to be able to build a prototype nuclear thermal rocket engine. NASA currently plans to launch a manned mission to Mars in 2039. According to a study commissioned by the National Academies of Sciences, Engineering, and Medicine [46], under such an aggressive time schedule, NTP development faces four major challenges: (1) the development of an NTP system that can heat its propellant to approximately 2700 K, which is the core exit for the duration of multiple burn cycles; (2) the need to rapidly bring an NTP system to full operating temperature in a very short time (e.g., on the order of a minute); (3) the long-term storage of LH2 with minimal loss during a mission; and (4) the lack of U.S. testing facilities for system testing.
