Key Performance Parameters for an Operational CIS-Lunar NTP Vehicle

Nuclear Thermal Propulsion (NTP) is in active development by NASA and DARPA. This paper presents an investigation into the effects of different values of key performance parameters (KPPs) of an NTP engine in the context of payload delivery missions between Earth and Lunar orbits. The high Isp afforded by NTP combined with the relatively large engine mass is best applied to missions where the payload mass is large and required ΔV high. Two missions considered are the round-trip Earth to Moon tug and a NRHO to low Lunar orbit tug. Chemical propulsion vehicles can generally achieve higher propellant mass fractions, similar payload mass and similar ΔV performance on these missions. When re-use of the vehicle is considered, the reduced propellant mass required by an NTP vehicle begins to add up over multiple refilling launches and trades more favorably. Analysis illustrates the impact of variation in NTP engine performance values, especially Isp, engine mass and thrust, on performance and the comparison to chemical propulsion. NTP transient and cooldown effects on the vehicle performance are examined. A variety of launch vehicles and hydrogen and ammonia NTP propellants are included in the analyses, and cryogenic fluid management system effects are accounted for.