Turbopump

A turbopump is the high-speed pump that forces fuel and oxidizer into a liquid-fueled rocket engine. It is essentially two machines on one spinning shaft, and it is part of what makes large orbital rockets possible.

Quick facts

• What it does: raises a rocket’s propellants (its fuel and the oxidizer that lets the fuel burn) to very high pressure and feeds them into the engine.
• Two core parts: a pump that pressurizes the propellant, and a turbine (a bladed wheel spun by a stream of gas) on the same shaft that drives the pump.
• Power density: enormous, roughly 20 times that of a car turbocharger. The Space Shuttle’s RS-25 fuel turbopump makes about 100 horsepower for every pound it weighs.
• Speed and pressure: commonly tens of thousands of revolutions per minute (rpm), feeding engines at hundreds of bar of pressure.

What it is and how it works

Picture two machines bolted to one spinning shaft. On the pump end, a screw-shaped piece called an inducer gently pressurizes the incoming propellant and hands it to an impeller, a spinning disc that flings the fluid outward at high speed. A surrounding chamber called a volute then converts that speed into pressure, squeezing the propellant to hundreds of bar.

On the other end of the shaft sits the turbine: rows of blades that catch a stream of hot, high-pressure gas. The gas pushes the blades, which spin the shaft, which spins the pump. To make that gas, a small amount of propellant is burned in a preburner or gas generator. So a little propellant is sacrificed to power the turbine, and the turbine drives the pump that forces the rest of the propellant into the main combustion chamber.

A key danger is cavitation: if the inlet pressure drops too low, the liquid boils into bubbles that pit and damage the blades. That is why nearly all turbopumps since the 1950s use an inducer, which raises the inlet pressure just enough to stop the liquid from boiling. Pump type also varies with the propellant. Dense liquids like RP-1 (a refined kerosene) and liquid oxygen usually use centrifugal pumps, which fling fluid outward; very light liquid hydrogen sometimes uses axial pumps, which push fluid straight along the shaft, for higher flow.

Why it matters

Turbopumps let rockets be both powerful and reasonably light. The alternative is a “pressure-fed” engine that simply relies on heavily pressurized tanks to push propellant in. That forces the tanks to be thick, heavy, and pressure-limited, which caps engine performance. By instead pumping propellant up to chamber pressure on the fly, turbopumps let tanks stay light while the combustion chamber runs at the high pressures needed for strong, efficient thrust. Essentially every large orbital launch vehicle that carries satellites or astronauts depends on turbopump-fed liquid engines.

How the turbine’s exhaust is handled defines the engine’s “cycle,” and that choice is one of the biggest factors in efficiency and reuse. A gas-generator cycle dumps the turbine exhaust overboard: simple and reliable, but it wastes a few percent of propellant. Staged-combustion and full-flow cycles instead route that gas onward into the main chamber so nothing is wasted, giving higher performance at the cost of far greater plumbing and engineering complexity.

Notable examples

• V-2 rocket (1942): an early turbopump driven by steam from decomposed hydrogen peroxide, feeding ethanol and liquid oxygen. One of the first practical rocket turbopumps.
• Rocketdyne F-1 (Saturn V): a single turbopump of about 55,000 horsepower fed each F-1 engine at roughly 5,500 rpm, moving about 15,471 US gallons per minute of RP-1 and about 24,811 of liquid oxygen. Five F-1s gave the Saturn V its Moon-bound thrust.
• RS-25 / Space Shuttle Main Engine: a staged-combustion engine with separate high-pressure fuel and oxidizer turbopumps. The fuel pump alone makes about 71,000 horsepower at roughly 35,000 rpm, boosting liquid hydrogen from about 276 to 6,515 psi. It is among the most complex turbopumps ever flown and now powers NASA’s SLS.
• SpaceX Raptor (Starship/Super Heavy): a full-flow staged-combustion methane/oxygen engine using two turbopumps and two preburners, one per propellant. It is the first full-flow staged-combustion engine to fly, designed for reuse by keeping the turbine gas relatively cool.
• Merlin (Falcon 9): a simpler gas-generator engine whose single turbopump dumps its turbine exhaust overboard.