SpaceX Merlin

Merlin 1D

Test firing of the Merlin 1D at SpaceX’s McGregor test stand
Country of origin	United States
Manufacturer	SpaceX
Application	Booster stage engines Upper stage engine
Associated LV	Falcon 1, Falcon 9, Falcon Heavy
Status	Active
Liquid-fuel engine
Propellant	LOX / RP-1
Cycle	Gas-generator
Performance
Thrust, vacuum	981 kN (221,000 lbf)[1]
Thrust, sea-level	845 kN (190,000 lbf)[1]
Throttle range	Sea level: 845 to 482 kN (190,000 to 108,300 lbf) (57%)[1] Vacuum: 981 to 626 kN (220,500 to 140,679 lbf) (64%)[1]
Thrust-to-weight ratio	184
Chamber pressure	9.7 MPa (1,410 psi)[2]
Specific impulse, vacuum	311 s (3.05 km/s)[3] [needs update]
Specific impulse, sea-level	282 s (2.77 km/s)[3] [needs update]
Dimensions
Diameter	Sea level: 0.92 m (3.0 ft) Vacuum: 3.3 m (11 ft)
Dry weight	470 kg (1,030 lb)[4]

Merlin is a family of rocket engines developed by SpaceX for use on its Falcon 1, Falcon 9 and Falcon Heavy launch vehicles. Merlin engines use RP-1 and liquid oxygen as rocket propellants in a gas-generator power cycle. The Merlin engine was originally designed for sea recovery and reuse, but since 2016 the entire Falcon 9 booster is recovered for reuse by landing vertically on a landing pad using one of its nine Merlin engines.

The injector at the heart of Merlin is of the pintle type that was first used in the Apollo Lunar Module landing engine (LMDE). Propellants are fed by a single-shaft, dual-impeller turbopump. The turbopump also provides high-pressure fluid for the hydraulic actuators, which then recycles into the low-pressure inlet. This eliminates the need for a separate hydraulic drive system and means that thrust vectoring control failure by running out of hydraulic fluid is not possible.