Raptor 2

Raptor 2 is the second-generation rocket engine SpaceX built to power Starship, its fully reusable launch system. It is a major redesign that delivers more thrust, runs hotter and harder, weighs less, and costs about half as much to build as the engine that came before it.

Quick facts

• Type: full-flow staged combustion (FFSC) cycle, methalox (liquid methane + liquid oxygen)
• Sea-level thrust: ~230 tons-force (2.26 MN; ~507,000 lbf), with SpaceX targeting up to 250 tf
• Vacuum variant (RVac) thrust: ~258 tf (2.53 MN; ~569,000 lbf)
• Specific impulse (a measure of fuel efficiency): ~347 s for the sea-level engine (SpaceX’s official figure); the vacuum variant, with its larger nozzle, is higher still (~356-380 s)
• Chamber pressure: ~300 bar — among the highest of any flown engine
• Mass: ~1,630 kg (down from ~2,080 kg for Raptor 1); thrust-to-weight ratio ~141
• Size: ~3.1 m long, ~1.3 m wide; throttle range 40-100%; mixture ratio ~3.6:1 (oxidizer-rich)
• Engine count: 33 on the Super Heavy booster, 6 on the Starship upper stage (3 sea-level + 3 vacuum)

What it is and how it works

Raptor 2 burns two liquids together: methane (the main ingredient in natural gas) as the fuel, and oxygen as the oxidizer (the substance that lets the fuel burn). Both are chilled well below their normal boiling points — a state engineers call subcooled, or deep-cryogenic. Cooling them makes them denser, so more mass fits in each tank, which boosts performance.

What makes Raptor 2 unusual is its full-flow staged combustion cycle. Before reaching the main combustion chamber (where the real burn happens), the propellants pass through two preburners — small chambers that burn a little of the mix to make hot gas that spins the turbopumps, the pumps that force propellant into the engine at enormous pressure. One preburner runs fuel-rich to drive the methane pump; the other runs oxidizer-rich to drive the oxygen pump. The key idea is that the entire flow of both propellants goes through these preburners and turbines first, then meets in the main chamber to finish burning. Think of it like pre-warming both ingredients fully before the final mix, so almost nothing is wasted.

This full-flow approach lets the turbines run cooler for a given amount of power, allows the very high chamber pressure of around 300 bar, and uses up essentially all the propellant. Because the preburner exhaust arrives already scorching hot, the main chamber needs no separate igniter (a spark-like device to start the burn). Raptor 2 uses coaxial swirl injectors — nozzles that spin the propellants together to mix them — rather than the pintle injectors found on SpaceX’s earlier Merlin engine.

Why it matters

Full-flow staged combustion is rare: Raptor 2 is one of only a handful of such engines ever flown, and it operates at among the highest chamber pressures of any production rocket engine. That combination makes it one of the most efficient and powerful engines of its class. It is central to SpaceX’s goal of a fully and rapidly reusable super-heavy rocket. Methane was chosen partly because it could, in theory, be manufactured on Mars (using a chemical process called the Sabatier reaction) to fuel return trips — supporting SpaceX’s long-term Mars ambitions.

Compared with Raptor 1, Raptor 2 was simplified for mass production: many bolted flanges were replaced with welds and parts were eliminated, cutting cost roughly in half. SpaceX reached a build rate of about one engine per day. With 33 of these engines firing together, a Super Heavy booster generates more combined liftoff thrust than any rocket in history.

Where it is used and notable examples

• Super Heavy booster: powered by 33 Raptor 2 engines; Booster 7 was the first to fly the full 33-engine configuration.
• Starship upper stage: uses 6 engines — 3 sea-level Raptor 2 plus 3 Raptor Vacuum (RVac) variants with large nozzles shaped for the vacuum of space.
• Starship integrated flight tests: from 2023 onward, the Starship/Super Heavy stack flew on Raptor 2 engines through most of its early test campaign.
• Raptor 1 (predecessor): the first-generation engine (~185 tf sea level, ~2,080 kg) that Raptor 2 replaced through a complete redesign.
• Raptor 3 (successor): targets ~280 tf, lighter and without an external heat shield; it first flew on Starship’s twelfth flight test in 2026, succeeding Raptor 2.