Liquidfueled

Liquidfueled refers to propulsion systems in which liquid propellants are stored separately and injected into a combustion chamber where they react to produce high-temperature, high-pressure gases that exit through a nozzle to generate thrust. This contrasts with solid-fuel motors, where the propellant is a single, solid mass. Liquidfueled engines are typically used in space launch vehicles and upper stages, as well as maneuvering and reaction control systems, because they offer controllable thrust, restart capability, and higher specific impulse than most solid systems.

Common oxidizers and fuels include liquid oxygen (LOX) combined with liquid hydrogen (LH2) for high efficiency, LOX with RP-1 (kerosene) for a balance of performance and density, and newer methane (LCH4) with LOX as a developing option. Engines may be pump-fed, using turbopumps to deliver propellants at high pressure, or pressure-fed, which are simpler but lower in performance. Cryogenic propellants require insulated tanks and venting to manage boil-off, adding complexity.

Advantages of liquid-fueled designs include high specific impulse, thrust controllability, and the ability to restart engines multiple times for orbital maneuvers or staged launches. Disadvantages include mechanical complexity, cooling and propellant management requirements, and safety concerns related to handling cryogenic liquids and high-pressure systems.

Notable examples include Space Shuttle Main Engines (LH2/LOX), modern LOX/LH2 engines used on upper stages, RP-1/LOX engines such as Merlin variants, and methane-based LOX/LCH4 engines like BE-4. Liquidfueled propulsion remains central to many current and planned spaceflight programs.