How SpaceX's Raptor engine works, one problem at a time

An interactive explainer builds the Raptor engine step by step, starting from a cold-gas thruster and adding one subsystem per engineering problem until reaching SpaceX’s full-flow staged-combustion design. It explains why tank pressure alone is useless for orbital flight, why turbopumps are essential (requiring tens of megawatts), and how traditional gas-generator and staged-combustion cycles differ. Key numbers and milestones are given: Raptor chamber pressures near 300 bar, first flight on Starhopper in July 2019, and thrust classes roughly 1,185 tf (Raptor 1), 2,230 tf (Raptor 2) and 3,280 tf (Raptor 3). Historical context notes only two prior full-flow efforts - RD-270 and the Integrated Powerhead Demonstrator - had been built but never flown.

The explainer then unpacks why full-flow staged combustion matters: splitting propellant through separate fuel-rich and oxygen-rich preburners eliminates dangerous mixed seals, yields cooler, longer-lived turbines, and delivers gaseous propellants to the main chamber for higher pressure and efficiency. It covers the metallurgy challenge of oxygen-rich hot gas (SpaceX’s custom alloy), regenerative cooling and throat film-cooling tradeoffs (Raptor 2 reportedly removed throat film cooling; Raptor 3 expanded regenerative cooling to avoid a heat shield), autogenous tank pressurization versus helium, and the delicate start sequence - whose failures forced a July 2026 Starship abort - plus the plumbing and control systems that make the cycle work in practice.