Engine cycle

The engine cycle of a rocket engine describes the primary method chosen to transport propellants into the combustion chamber. Real rocket engines can have multiple different engine cycles active during their operation in sequence, for optimal performance at different thrust levels or during ignition and cut-off.

Pressure-feed

The simplest engine cycle is the pressure-feed. It relies on the ullage pressure of the tanks to push the propellants into the combustion chamber. It is very robust and such an engine can easily be started and cut-off, which makes this cycle preferred for RCS and restartable main engines.

Gas-generator cycle

The gas generator cycles uses a gas generator and a turbine to drive a pump, which transports the fuel into the combustion chamber