Liquid propellant engines are a type of rocket engine that use liquid fuels and oxidizers to produce thrust. These engines mix the fuel and oxidizer in a combustion chamber, where they ignite and create high-pressure gases that are expelled through a nozzle. This process generates the necessary force to propel a rocket into space. One of the main advantages of liquid propellant engines is their ability to be throttled, allowing for precise control of thrust. They are commonly used in various space missions, including those involving NASA and SpaceX, due to their efficiency and reliability compared to solid propellant engines.