Only NASA’s Saturn V, which sent Americans to the moon, has ever generated more power. In rockets, the most important measure of power is thrust. Falcon Heavy’s 27 individual booster engines together generate 3.8 million pounds of thrust—enough to lift the 3.1-million-pound rocket and its 117,000-pound payload toward low-Earth orbit. The rocket’s success is critical for both SpaceX and the U.S. space program: The Air Force has already hired SpaceX and its Falcon Heavy to send two satellites into orbit sometime in 2015.