How SpaceX's Raptor engine works, one problem at a time
a day ago
- Rocket propulsion starts with expelling mass: cold gas thrusters are simple but low thrust; chemical rockets use combustion for higher energy.
- Pressure-fed engines require heavy tanks to achieve high chamber pressure; turbopumps solve this by feeding propellant at low tank pressure.
- Gas generator engines (e.g., Merlin) waste propellant by dumping turbine exhaust; staged combustion recirculates exhaust into the main chamber for efficiency.
- Full flow staged combustion (Raptor) uses two independent preburners, eliminating dangerous seals, allowing higher chamber pressure, and enabling engine reuse.
- Raptor 1 was a development engine with many sensors and bolts; Raptor 2 reduced mass by deleting spark igniters and merging parts; Raptor 3 integrated plumbing, removed heat shield, and replaced helium with nitrogen.
- SpaceX's iterative approach—build many engines, delete parts first, then simplify—led to Raptor 3 being 25% lighter and 50% more powerful than Raptor 1.
- Support systems include regenerative cooling (fuel flows through chamber walls), tank pressurization with autogenous gas, and a complex start sequence involving chill-down, purge, and spin-up.