liquid-propellant rocket engine
A liquid-propellant rocket engine is a rocket propulsion system that uses a liquid propellant, combining a liquid fuel (such as kerosene or liquid hydrogen) in a thrust chamber with a liquid oxidizer (such as liquid oxygen or fuming nitric acid). Very efficient and controllable, such engines are used extensively in spaceflight. Unlike solid-propellant rocket motors, they can be shut off by remote command, simply by closing off their fuel line. In some cases, the thrust can also be varied over a certain range.