Raptor

Overview

Raptor is SpaceX's full-flow staged combustion (FFSC) methalox engine that powers Starship and Super Heavy. It's the only FFSC engine ever to fly (the Soviet RD-270 was tested but cancelled). Both propellants enter the main chamber as hot gas, enabling industry-leading chamber pressure and ~5% more specific impulse than a gas-generator engine at the same expansion ratio. Headline numbers (Raptor 2 baseline per SpaceX briefings; Raptor 3 figures Musk-stated targets): Isp ~330s sea-level / ~380s vacuum (est., vacuum variant); chamber pressure 300 bar (R2) → 350 bar target (R3); O/F mixture ratio ~3.6 (methalox-rich-on-the-LOX-side vs stoichiometric 4.0, run slightly fuel-rich to cap chamber temperature); thrust ~230 tf sea-level (R2) → 280+ tf target (R3); thrust-to-weight ~200:1 (R2) → ~250:1 target (R3, ~1500 kg dry); throttling 40-100% (deep-throttle for Starship landing). Throat diameter ~0.2m. Sources: spacex.com/vehicles/starship, Eric Berger / Ars Technica reporting, NASASpaceflight forum technical analysis.