What Is the Raptor Engine? SpaceX's Starship Powerplant

Raptor is the rocket engine SpaceX designed from scratch to power Starship. What makes it remarkable isn’t just its thrust — it’s the way it works. Raptor burns liquid methane and liquid oxygen using a full-flow staged combustion cycle, a notoriously hard design that no engine had ever flown operationally before SpaceX pulled it off. The result is a compact, high-pressure, mass-producible engine that the whole Starship vehicle is built around. Here’s what that actually means.

What the Raptor engine is

Raptor is a methalox engine — “methalox” being shorthand for the methane-plus-oxygen propellant combo it burns. Dozens of them fly on a single Starship stack: the giant Super Heavy booster is lifted by a cluster of Raptors, and the Starship upper stage carries several more. For the full breakdown of how many fly where, see how many engines Starship has.

Three choices define the engine and explain almost everything about it:

Methane fuel, instead of the kerosene most boosters use.
Full-flow staged combustion, instead of a simpler, more wasteful cycle.
Mass production, instead of hand-built one-offs.

Each of those was a deliberate bet, and each is worth unpacking.

Full-flow staged combustion, in plain English

Every rocket engine has to feed enormous amounts of propellant into the combustion chamber, and it uses pumps to do it. Those pumps are themselves driven by burning a little propellant in preburners. The question is what happens to that preburner exhaust.

Simpler engines burn a bit of propellant just to spin the pumps and then dump that exhaust overboard — wasted energy literally thrown out the side. Better engines route it back into the main chamber. Full-flow staged combustion goes all the way: it runs two preburners, sends all of the fuel and all of the oxygen through them to drive the pumps, and then feeds everything into the main chamber to burn. Almost nothing is wasted.

The payoff is high efficiency and very high chamber pressure from a relatively small engine — but the design is brutally hard. Running both propellants through their own preburners, at extreme temperatures and pressures, is why no one had flown this cycle operationally before Raptor. SpaceX spent years iterating to make it reliable.

Why methane instead of kerosene or hydrogen

Most boosters historically burned kerosene (RP-1). Raptor went with methane for a stack of reasons:

It’s cleaner-burning than kerosene, which leaves sooty residue that complicates rapid reuse. Cleaner combustion suits an engine meant to fly again and again with little refurbishment.
It’s far easier to store and handle than hydrogen, which is ultra-cold, leak-prone and bulky. Methane is a practical middle path — more efficient than kerosene, far less troublesome than hydrogen.
It can, in principle, be made on Mars. Methane can be synthesized from Martian atmospheric CO₂ and subsurface water ice. An engine that runs on methane is a bet on refueling somewhere other than Earth — which is the entire point of Starship.

Why so many small Raptors instead of a few giant ones

Most heavy rockets use a handful of very large engines. SpaceX went the opposite way: lots of smaller Raptors clustered together. That choice buys two things.

First, engine-out capability. A rocket with three engines can’t afford to lose one mid-flight. A booster with dozens of Raptors can shut down a failed engine and rebalance thrust across the rest, often still completing the mission.

Second, manufacturability. It’s far easier to mass-produce one engine design thousands of times than to hand-build a few colossal ones. Raptor is meant to roll off a production line like a car part — and cheap, frequent engines are what make cheap, frequent flight possible. That production mindset is the same logic behind how SpaceX lands rockets to reuse them.

Sea-level vs. vacuum Raptors

Raptor comes in two flavors, because an engine optimized for thick lower atmosphere is wrong for the vacuum of space:

Sea-level Raptor — nozzles sized for use in the atmosphere. These steer (gimbal) and handle the dramatic landing maneuvers.
Raptor Vacuum (RVac) — much larger bell nozzles tuned for space, where there’s no air pressure to fight, making them far more efficient once Starship is above the dense atmosphere.

That split is what lets the vehicle punch off the pad and then cruise efficiently in orbit. To see how the whole vehicle uses them, read what Starship is, and for the broader company, what SpaceX is.

FAQ

What fuel does the Raptor engine use?

Raptor burns liquid methane and liquid oxygen, a combination nicknamed “methalox.” SpaceX chose methane because it burns cleanly for reuse, is easier to handle than hydrogen, and could one day be manufactured on Mars to refuel returning ships.

What is full-flow staged combustion?

It’s an engine cycle that routes all of the fuel and all of the oxygen through preburners to drive the pumps, then burns everything in the main chamber — wasting almost no propellant. It’s extremely efficient but very hard to build, and Raptor was the first to fly it operationally.

Why does SpaceX use so many Raptor engines?

Clustering many smaller engines gives “engine-out” capability — the rocket can lose an engine and keep flying — and lets SpaceX mass-produce one design instead of hand-building a few giant engines. Cheap, repeatable engines are key to flying often and affordably.

What’s the difference between Raptor and Raptor Vacuum?

The sea-level Raptor has a smaller nozzle for use in the atmosphere and handles steering and landing. Raptor Vacuum (RVac) has a much larger nozzle optimized for space, where it runs far more efficiently once the ship is out of the thick lower atmosphere.

Engine specifications evolve with each Starship version. Details here reflect the current operational design and are reviewed periodically.