Liquid rocket engines are propulsion systems that use liquid propellants to produce thrust. These engines typically consist of a combustion chamber where fuel and an oxidizer are mixed and ignited. The resulting high-pressure gases are expelled through a nozzle, generating thrust that propels the rocket forward. One of the main advantages of liquid rocket engines is their ability to be throttled, allowing for precise control of thrust during flight. They are commonly used in various space missions, including those involving NASA and SpaceX, due to their efficiency and reliability compared to solid rocket engines.