The SpaceX Merlin Engine: The Power Behind the Falcon Rockets

spacex falcon heavy
Credit: SpaceX

In the ever-evolving landscape of space exploration, one technological marvel continues to capture our imagination – the Merlin rocket engine.

Developed and manufactured by SpaceX, the aerospace company founded by visionary entrepreneur Elon Musk, the Merlin engine lies at the heart of some of the most iconic achievements in recent rocketry.

The Merlin rocket engine family serves as the propulsion backbone for SpaceX’s Falcon rockets – the Falcon 1, Falcon 9, and the Falcon Heavy.

Its name draws inspiration from the mythical wizard Merlin of Arthurian legend, embodying the magical innovation that propels humanity beyond our planet’s boundaries.

spacex merlin engine design
Credit: Brian Haeger

The Ingenious Design

The Merlin engine operates on a liquid-propellant system, pairing rocket-grade kerosene (RP-1) as fuel with liquid oxygen (LOX) as the oxidizer.

Its vertical takeoff and landing (VTVL) capabilities, a significant breakthrough, amplify its efficiency and reusability – cornerstones of SpaceX’s mission to make space travel more accessible.

merlin engine 1d
Credit: SpaceX

The Merlin 1D+ engine, the latest major revision of the Merlin series, boasts impressive specifications. It generates approximately 190,000 pounds-force (lbft) of thrust in a vacuum and around 180,000 lbf at sea level.

With a vacuum-specific impulse of approximately 311 seconds and a sea-level-specific impulse of about 282 seconds, the engine strikes a balance between efficiency and power.

Its dimensions include an engine length of roughly 3.7 meters (12 feet) and an engine diameter of approximately 1.2 meters (4 feet).

Weighing in at around 470 kilograms (1,036 pounds), the engine’s performance capabilities are a result of meticulous engineering and innovative design.

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At the heart of the Merlin engine’s prowess lies the gas generator cycle – a staged combustion technique that extracts remarkable energy from propellants.

A fraction of the propellant undergoes controlled combustion in the gas generator, driving the engine’s turbopumps.

These pumps ensure a steady flow of fuel and oxidizer to the combustion chamber, enabling precise control over thrust and efficiency.

Merlin Engine Reusability

Undoubtedly, one of the most revolutionary facets of the Merlin engine lies in its pivotal contribution to SpaceX’s reusability.

At the heart of this breakthrough is the game-changing ability to land and recover the first stage of the Falcon 9 rocket, which houses multiple Merlin engines.

This transformative capability has ushered in a new era of economics in space travel, redefining the traditional cost structures associated with rocket launches.

The seamless integration of the Merlin engine into this reusability strategy is a testament to SpaceX’s commitment to innovation and efficiency.

History of the Merlin Engine Development

The Merlin engine has undergone a transformative journey, with each iteration amplifying its capabilities.

  • 1. Merlin 1A: The debutante Merlin engine featured an expendable ablative cooled carbon-fiber-reinforced polymer composite nozzle, producing around 77,000 pounds-force (lbft) of thrust at sea level.
  • 2. Merlin 1B: The upgraded version, the Merlin 1B, offered enhanced thrust capabilities of approximately 92,500 lbf at sea level, solidifying its role in the Falcon 1 rocket.
  • 3. Merlin 1C: The Merlin 1C showcased an increased thrust of about 90,000 lbf at sea level, accompanied by efficiency improvements and an enhanced expansion ratio.
  • 4. Merlin 1D: A significant milestone, the Merlin 1D engine powered the Falcon 9 rocket, boasting around 190,000 lbf of thrust in vacuum and 180,000 lbft at sea level.
  • 5. Merlin 1D Vacuum: Optimized for vacuum operation, the Merlin 1D Vacuum‘s higher nozzle expansion ratio enhances its performance in the vacuum of space.
  • 6. Merlin 1D+ (Block 5): The latest iteration, Merlin 1D+, propels the Falcon 9 Block 5 variant, featuring upgrades in thrust, thermal protection, durability, and reusability.

Pros and Cons of the Merlin Engine


  • Exceptional Performance: With its high thrust and specific impulse, the Merlin engine enables efficient launches and effective payload delivery.
  • Reusability Champion: Engineered for reusability, the Merlin engine significantly reduces mission costs by allowing the recovery and refurbishment of rocket stages.
  • Versatile Solution: Successfully integrated into various SpaceX rockets, including Falcon 1, Falcon 9, and Falcon Heavy, the Merlin engine demonstrates its adaptability and versatility.
  • Precision in Control: Thrust vector control provides meticulous guidance over the rocket’s trajectory, allowing for precise maneuvers and accurate payload delivery.
  • Unwavering Reliability: SpaceX’s consistent record of successful launches and missions underscores the Merlin engine’s reliability.


  • Complex Design Challenges: The intricate nature of the engine’s gas generator cycle and turbopump system adds complexity to its design and operation.
  • Development Hurdles: The engine’s technology required extensive research, testing, and iterative improvements, posing challenges during its development and refinement.
  • Manufacturing Intricacy: The production of Merlin engines demands advanced manufacturing techniques and precision engineering due to its intricate components.
  • Propellant Handling Complexity: Managing the storage, transport, and handling of highly flammable propellants (RP-1 and LOX) presents challenges requiring specialized precautions.
  • Technical Limitations: The engine’s performance encounters technical thresholds, including temperature and pressure limitations that impact its operation.


Ultimately, the Merlin rocket engine remains a beacon of innovation and progress in the realm of space exploration.

With each iteration, SpaceX redefines what’s possible, not just within our atmosphere but beyond.

As humanity dreams of interplanetary journeys and ventures to the stars, the Merlin engine will continue to be an instrumental force in making those dreams a reality.

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