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The Merlin engine that powers the first stage of Falcon 9 is developed and manufactured in-house by SpaceX. Burning liquid oxygen and rocket-grade kerosene propellant, a single Merlin engine emits 845 kilonewtons (190,000 pounds) of thrust at liftoff, rising to 914 kilonewtons (205,500 pounds) as it climbs out of Earth’s atmosphere. Merlin’s thrust-to-weight ratio exceeds 150, making the Merlin the most efficient booster engine ever built, while still maintaining the structural and thermal safety margins needed to carry astronauts.
Falcon 9 is the only vehicle currently flying with engine out capability; Falcon 9 can lose up to two of its Merlin engines on the first stage and still complete its mission. The nine-engine architecture on the first stage is an improved version of the design employed by the Saturn I and Saturn V rockets of the Apollo program, which had flawless flight records in spite of engine losses.