Musk initially planned that this next rocket would have five engines rather than one, and thus be called the Falcon 5. It would also need a more powerful engine. But Tom Mueller worried that it would take too long to build a new engine, and he persuaded Musk to accept a revised idea: a rocket with nine of the original Merlin engines. Thus was born the Falcon 9, a rocket that would become the workhorse of SpaceX for more than a decade. At 157 feet, it was more than twice as tall as the Falcon 1, ten times more powerful, and twelve times heavier.
