Merlin is a family of rocket engines developed by SpaceX. They are currently a part of the Falcon 9 and Falcon Heavy launch vehicles, and were formerly used on the Falcon 1. 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. The engine is named after Merlin (a falcon).
