Physics / mechanism
Nuclear thermal propulsion (NTP) heats propellant—typically liquid hydrogen—by passing it through or around a fission reactor core, then expands it through a nozzle. No combustion. Thrust derives purely from thermal energy transfer to propellant mass. Key figure of merit: specific impulse (Isp). Chemical rockets (LOX/LH2) achieve ~450 s Isp; NTP targets 800–1,000 s, roughly doubling propellant efficiency. Thrust-to-weight ratios are modest (~3–10), so NTP suits in-space transit, not launch. NERVA (1960s–70s) demonstrated ~1,100 MW reactor operation and ~825 s Isp at TRL 5–6. Current programs: DARPA/NASA DRACO (Demonstration Rocket for Agile Cislunar Operations), targeting a 2027 orbital test using low-enriched uranium (LEU) to sidestep enrichment politics.
Competitive landscape
DRACO’s direct competitors for cislunar/Mars transit are nuclear electric propulsion (NEP—high Isp ~3,000–10,000 s but low thrust, long burn arcs) and advanced chemical (low Isp ceiling, no regulatory drag). Solar electric propulsion competes on cost but degrades beyond ~2 AU.
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.