NUCLEAR THERMAL ROCKET/VEHICLE CHARACTERISTICS AND SENSITIVITY TRADES FOR NASA’s MARS DESIGN REFERENCE ARCHITECTURE (DRA) 5.0 STUDY

This paper summarizes Phase I and II analysis results from NASA’s recent Mars DRA 5.0 study which re-examined mission, payload and transportation system requirements for a human Mars landing mission in the post-2030 timeframe. Nuclear thermal rocket (NTR) propulsion was again identified as the preferred in-space transportation system over chemical/aerobrake because of its higher specific impulse (Isp) capability, increased tolerance to payload mass growth and architecture changes, and lower total initial mass in low Earth orbit (IMLEO) which is important for reducing the number of Ares-V heavy lift launches and overall mission cost. DRA 5.0 features a long surface stay (~500 days) “split mission” using separate cargo and crewed Mars transfer vehicles (MTVs). All vehicles utilize a common “core” propulsion stage with three 25 klbf “composite fuel” NERVA-derived NTR engines (Tex ~2650 2700 K, pch ~1000 psia, ~300:1, Isp ~900 910 s, engine thrust-toweight ratio ~3.43) to perform all primary mission maneuvers. Two cargo flights, utilizing “1-way” minimum energy trajectories, pre-deploy a cargo lander to the surface and a habitat lander into a 24-hour elliptical Mars parking orbit where it remains until the arrival of the crewed MTV during the next mission opportunity (~26 months later). The cargo payload elements aerocapture (AC) into Mars orbit and are enclosed within a large triconicshaped aeroshell which functions as payload shroud during launch, then as an aerobrake and thermal protection system during Mars orbit capture and subsequent entry, descent and landing (EDL) on Mars. The “all propulsive” crewed MTV is a “0-gE” vehicle design that utilizes a ”fast conjunction” trajectory that allows ~6-7 month “1-way” transit times to and from Mars. Four 12.5 kWe / 125 m 2 rectangular photovoltaic arrays provide the crewed MTV with ~50 kWe of electrical power in Mars orbit for crew life support and spacecraft subsystem needs. Vehicle assembly involves autonomous Earth orbit rendezvous and docking between the propulsion stages, in-line propellant tanks and payload elements. Nine Ares-V launches -five for the two cargo MTVs and four for the crewed MTV -deliver the key components for the three MTVs. Details on mission, payload, engine and vehicle characteristics and requirements are presented and the results of key trade studies are discussed.