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Merlin engines power SpaceX’s Falcon rockets, while Raptor engines power the Starship system. Both burn liquid oxygen with a fuel and use turbopumps to feed a combustion chamber, but Merlin burns kerosene in a gas-generator cycle and Raptor burns methane in a staged-combustion cycle. That difference describes how each engine powers its turbines and routes the resulting gas.
What the engines do
A rocket engine produces thrust by accelerating hot exhaust through a nozzle. The exhaust moves one way; the rocket is pushed in the opposite direction.
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Merlin: Falcon launch and upper-stage power
Merlin is SpaceX’s engine family for Falcon vehicles. Falcon 9 uses nine Merlin 1D engines on its first stage and one Merlin Vacuum engine on its second stage, according to NASA’s Falcon 9 overview and SpaceX’s Falcon 9 page. The engines burn liquid oxygen (LOX) and rocket-grade kerosene (RP-1).
Raptor: Starship and Super Heavy power
Raptor powers Starship, the SpaceX transportation system made up of the Starship spacecraft and the Super Heavy rocket. It burns LOX and methane. SpaceX describes Raptor as reusable and staged-combustion; its Starship page also says Raptor has twice the thrust of the Falcon 9 Merlin engine.
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How their power cycles work
Both engines use turbomachinery to pump propellants into a high-pressure combustion chamber. The fuel and oxidizer react there, and the nozzle turns the hot gas’s energy into exhaust velocity and thrust. The cycle explains how the turbines that drive the pumps get their power—and whether their exhaust joins the main flow.
Merlin’s gas-generator cycle
Merlin uses a gas generator: a small amount of propellant burns separately to make hot gas, which drives a turbine connected to the turbopumps. That turbine exhaust is discharged separately rather than being routed through the main combustion chamber and nozzle. This is a comparatively straightforward cycle, but the turbine-driving gas does not contribute to the main chamber’s exhaust flow. SpaceX’s Falcon User’s Guide identifies Merlin as a gas-generator engine.
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Raptor’s staged-combustion cycle
Raptor uses staged combustion. At a high level, propellant burns in preburner(s) to make hot gas that drives the turbines; that gas then enters the main combustion chamber, where combustion is completed before the exhaust leaves through the nozzle. Unlike a gas-generator arrangement, the turbine-driving gas contributes to the main chamber flow. SpaceX identifies Raptor’s cycle as staged combustion, but the cited page does not provide a complete plumbing schematic or describe every Raptor variant’s hardware.
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These figures describe specific Merlin variants or a qualified SpaceX comparison; they are not a matched test of the two engine families under identical conditions.
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| Engine or claim | Published figure | Qualification |
|---|---|---|
| Merlin sea-level variant | 845 kN (190,000 lbf) | Listed on SpaceX’s current Falcon 9 engine page, accessed in 2026. |
| Merlin Vacuum, Falcon 9 second stage | 981 kN (220,500 lbf); listed burn time: 397 seconds | Figures listed on SpaceX’s current Falcon 9 page, accessed in 2026. |
| Falcon 9 first-stage Merlin 1D engines | Nine engines; up to 845 kN (190,000 lbf) per engine | Specification in SpaceX’s 2025 Falcon Payload User’s Guide. |
| Raptor relative thrust statement | Twice the thrust of the Falcon 9 Merlin engine | SpaceX’s current Starship page, accessed in 2026; the cited passage does not identify the matched variant or operating condition and does not give an exact Raptor thrust figure. |
The comparison is useful as SpaceX’s broad description, not as a same-condition measurement. The available figures do not establish a quantified efficiency, reliability, cost, or service-life advantage for either family.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare Merlin and Raptor
| Comparison point | Merlin | Raptor |
|---|---|---|
| Propellants | LOX and RP-1 kerosene | LOX and methane |
| Power cycle | Gas generator | Staged combustion |
| Vehicle role | Falcon first and second stages | Starship and Super Heavy system |
| Published thrust evidence | SpaceX lists figures by sea-level and vacuum variant. | SpaceX states twice the thrust of the Falcon 9 Merlin engine; the cited passage provides no matched condition or exact Raptor figure. |
The practical distinction is not that one engine is simply “better.” They use different propellants, cycles and launch systems, and the published numbers here are not enough to establish a universal performance ranking.
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