Merlin is a rocket engine developed by SpaceX for use on its Falcon 1 and Falcon 9 rockets. Merlin uses RP-1 and liquid oxygen as propellants in a gas-generator power cycle. The Merlin engine is designed for sea recovery and reuse.
The injector at the heart of Merlin is of the pintle type that was first used in the Apollo Program for the lunar module landing engine.
Propellants are fed via a single shaft, dual impeller turbo-pump. The turbo-pump 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 power system and means that thrust vector control failure by running out of hydraulic fluid is not possible. A third use of the turbo-pump is to provide power to pivot the turbine exhaust nozzle for roll control purposes.