NTR Development Strategy and Key Activities Supporting NASA Human Mars Missions in the Early-2030 Timeframe

Abstract

In NASA’s recent Mars DRA 5.0 study, mission, payload and transportation system options and requirements for a human Mars mission in the 2031-2033 timeframe were examined. The nuclear thermal rocket (NTR) was selected as the preferred in-space propulsion option because of its high thrust, high specific impulse (Isp), and high TRL demonstrated in extensive ground tests during the Rover/NERVA programs. With a factor of 2 increase in Isp over LOX/LH2 chemical rockets, the NTR-based Mars transportation system requires less initial mass in low Earth orbit (IMLEO) and has increased tolerance to payload mass growth and architecture changes, features important for reducing the heavy lift launch count, overall mission cost and risk. DRA 5.0 featured a long surface stay “split mission” using separate cargo and crewed Mars transfer vehicles (MTVs). All vehicles utilized a common “core” propulsion module with three 25 klbf “composite fuel” NERVA-derived engines (Tex ~2700 K, pch ~1000 psia, e ~300:1, Isp ~900 s, engine thrust-to-weight ratio ~3.43) to perform all primary mission maneuvers. The total engine burn time and restart requirement for the crewed MTV out to Mars and back was ~75 minutes with 3 restarts. Engine size, fuel options, and performance requirements identified in DRA 5.0 are discussed in this paper and compared to technology capabilities demonstrated in Rover/NERVA, its supporting programs and today’s cryogenic chemical engines. To ensure a flight qualified NTR is available when needed, a technology recovery and demonstration effort with appropriate and sustained funding must begin immediately. Technology development needs, options being considered for affordable ground testing and key NTR development schedule activities are presented and discussed.