How does a rocket engine work?

A clear explanation of how SpaceX’s Raptor 2 turns liquid methane and oxygen into thrust, using the engine to introduce the engineering problems rockets must solve. Raptor burns about 700 kilograms of propellant per second, producing gas hotter than 3,000°C and ejecting it at roughly 3.2 kilometres per second. It generates about 230 tonnes-force, and its unusual full-flow staged-combustion cycle sends nearly all the fuel and oxygen through separate turbines to drive two pumps before everything burns in the main chamber. The discussion also previews the engine’s other key systems: preburners, fuel-based cooling, and a throat and bell that accelerate exhaust.

The first section explains why a rocket can move through a vacuum: it gains momentum by throwing exhaust backward, not by pushing against air. A cart that launches steel balls illustrates the principle; each ball’s momentum produces an equal kick in the opposite direction, and a continuous stream of exhaust does the same for a rocket. Thrust depends on how much mass is expelled and how fast it travels, with higher exhaust speed reducing the propellant needed for a given push. Air actually reduces Raptor’s thrust at sea level: pressure acting on the nozzle exit subtracts about 135 kilonewtons, so the engine produces roughly 6% more thrust in space.