The rocket engine is a deceptively simple piece of technology. Of the various forms, liquid bipropellant engines are most commonly used.

In a liquid bipropellant rocket engine, there are three main steps in producing thrust.

1. A fuel and oxidiser are delivered to the injection system in a pressurised state.
2. These propellants are then atomised and mixed before being ignited in the combustion chamber.
3. The combusted flow is accelerated through a convergent-divergent nozzle.

Due to the conservation of momentum, the high velocity exhaust causes a proportional increase in the velocity of the rocket (in the opposite direction).