Nuclear Thermal Rocket/Stage Technology Options for NASA's Future Human Exploration Missions to the Moon and Mars

The nuclear thermal rocket (NTR) provides a unique propulsion capability to planners and designers of future human exploration missions to the Moon and Mars. In addition to its high specific impulse (Isp ∼ 850–1000 seconds) and engine thrust‐to‐weight ratio (∼ 3–10), the NTR can also be configured as a “dual mode” system capable of generating stage electrical power. At present, NASA is examining a variety of mission applications for the NTR ranging from an expendable, “single burn” trans‐lunar injection (TLI) stage for NASA's “First Lunar Outpost” (FLO) mission to all propulsive, “multi‐burn,” spacecraft supporting a “split cargo/piloted sprint” Mars mission architecture. Two “proven” solid core NTR concepts are examined ‐one based on NERVA (Nuclear Engine for Rocket Vehicle Application)‐derivative reactor (NDR) technology, and a second concept which utilizes a ternary carbide “twisted ribbon” fuel form developed by the Commonwealth of Independent States (CIS). Integrated systems and mission study results are used in designing “aerobraked” and “all propulsive” Mars vehicle concepts which are mass‐, and volume‐compatible with both a reference 240 metric tonne (t) heavy lift launch vehicle (HLLV) and a smaller 120 t HLLV option. For the “aerobraked” scenario, the 2010 piloted mission determines the size of the expendable trans‐Mars injection (TMI) stage which is a growth version of the FLO TLI stage. An “all‐propulsive” Moon/Mars mission architecture is also described which uses common “modular” engine and stage hardware consisting of: (1) clustered 15 thousand pounds force (klbf) NDR or CIS engines; (2) two “standardized” liquid hydrogen (LH₂) tank sizes; and (3) “dual mode” NTR and refrigeration system technologies for long duration missions. The “modular” NTR approach can form the basis for a “faster, safer, and cheaper” space transportation system for tomorrow's piloted missions to the Moon and Mars.