Four families of chemical engine cycle
- Pressure-fed — Propellant tanks are pressurised; no turbopumps. Simple, low performance, low chamber pressure. Used in spacecraft thrusters (AJ10, Dracos).
- Gas-generator — A small fraction of propellant drives a turbopump; the exhaust is dumped overboard. Loses Isp but simple to engineer. Merlin, RS-27, F-1.
- Staged combustion — Turbopump exhaust is routed back into the main chamber. Higher Isp at the cost of plumbing complexity and extreme pressures. RD-180, SSME, RS-25, Raptor (full-flow staged).
- Expander — Fuel is heated by the nozzle and used to drive the turbopump before injection. Clean but limited in size. RL10, Vinci.
Full-flow staged combustion
Both fuel-rich and oxidiser-rich preburners drive separate turbines. Nothing is wasted. SpaceX Raptor is the first operational full-flow staged combustion engine in history.
Check your understanding below.