Technology Maturation Plan for High Power Nuclear Electric Propulsion

Nuclear electric propulsion (NEP), which uses a fission reactor to power electric thrusters, has been advanced as an option to propel a human mission to Mars since the late 1950s. The high specific impulse of electric thrusters (thousands of seconds) offers the potential to significantly reduce the required propellant mass for propulsively-challenging, high ∆v missions compared with thermodynamically limited conventional chemical propulsion systems that operate at up to 360-460s of specific impulse. Projected NEP benefits have not been realized despite major NASA investments in the Space Nuclear Auxiliary Propulsion program in the 1960s, the Space Exploration Initiative in the 1990s, and Project Prometheus in the early 2000s. A critical review by the National Academies of Sciences, Engineering, and Medicine (NASEM) indicated that the core issue hindering high-power NEP has historically been the lack of coordinated research and development focused on the demonstration of technically mature (TRL 5) MWe-class hard- ware. This finding was reinforced in a review of nuclear propulsion technical maturity by the NASA Engineering and Safety Center (NESC), which concluded that most of the key NEP technologies are currently at or below TRL 4 at the component level and lower still at the subsystem and system levels. The NESC review further indicated that for many of the technologies the advancement degree of difficulty (AD2) – a descriptive term to quantify the difficulty in advancing the readiness of a technology for a given application – was high enough to warrant an approach with multiple development paths to minimize the overall advancement risk. As a response to the NASEM and NESC findings, the Space Nuclear Propulsion (SNP) project developed this focused Technology Maturation Plan (TMP) as a roadmap for the technology advancements required to support informed decisions on the efficacy of NEP systems for humanrated Mars missions in the late 2030s. This mission timeframe aligns with the NASEM baseline assumptions, and it drove the project to develop a four-year technology maturation schedule to achieve TRL 5 in the mid-to-late 2020s to support the 2030s design of NEP-propelled cargo and human missions to Mars.