The J-2 Engine was the first liquid-hydrogen-fueled American rocket engine and is best known for powering the second and third stages of the Saturn V rocket for NASA's Apollo moon missions, supporting America's successful mission of discovery to the moon. Its innovative design spawned numerous engine development programs, including the space shuttle main engine. Today, engineers at NASA's Marshall Space Flight Center and Pratt and Whitney Rocketdyne Inc. are developing the next generation, the J-2X, to boost the upper stage of the Ares I crew launch vehicle to orbit and help tomorrow's explorers. The J-2 used liquid oxygen and liquid hydrogen propellants in a 5.5 mix, produced 200,000 pounds of thrust at sea level, stood 11.1 feet high, measured 6.8 feet in diameter, weighed 3,480 pounds dry, first flew in 1966, last flew in 1975, and flew 87 times.