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The SpaceX Merlin engines power the Falcon 9 first stage. After the engines are ignited the rocket is still clamped and not allowed to launch until all systems are "go." The engines provide 125,000 lbs-f sea level thrust per engine for a total thrust on liftoff of just over 1.1 Million lbs-f.
Learning from early rocket failures, SpaceX uses 9 engines that can propel a successful mission even if an engine malfunctions similar to what happened with the Saturn 1 and Saturn 5 rockets during the Apollo launches.