The R-7 rocket that launched Sputnik was a technological tour de force and a tremendous challenge to the West. Not only had Soviet scientists, led by legendary rocket designer Sergei Korolev, developed a rocket capable of flinging nuclear weapons to U.S. soil, they had opened the path to the moon and beyond. "The present generation will witness how the freed and conscious labor of the people of the new socialist society turns even the most daring of mankind's dreams into reality," declared a Soviet press release. A month later the Soviets launched 1,120-pound (508 kilograms) Sputnik 2, six times heavier than its predecessor, with a dog named Laika aboard. Laika lasted only a few hours in the overheated spacecraft, but the Russians had made their point: If they could put a dog in orbit, they could send a human. Wernher von Braun, the transplanted Nazi scientist who would build the Saturn V rocket that launched the Apollo moon missions, begged Neil McElroy, the incoming secretary of defense: "For God's sake turn us loose." Over the next few years, both the U.S. and the Soviet Union developed distinctive technologies, but they faced the same basic challenges. The physics of launch were, and are, immutable. An object flung into space has to reach a speed of between 17,000 and 18,000 miles an hour (27,000 and 28,000 kilometers) to attain low Earth orbit. To escape Earth's gravity altogether and fly somewhere else, a spacecraft must travel 25,000 miles an hour (40,000 kilometers). The heavier the payload, the more powerful the rocket must be, and in this the Soviets initially had a huge advantage with the R-7. Four months after Sputnik, the U.S. did manage to orbit its first satellite, 31-pound (14 kilograms) Explorer 1—but by the end of the year the Soviets had launched Sputnik 3, weighing in at a ton and a half (1.36 metric tons). The ensuing rivalry produced a procession of spectacular achievements and heroes. In 1961 Soviet cosmonaut Yuri Gagarin, only 27, became the first human in space, circling the Earth once and parachuting home to a soft landing in a plowed field. The next year, former Marine combat pilot John Glenn—later a U.S. senator—became the first American to orbit the Earth. In 1963 came the first woman in space, Soviet textile worker Valentina Tereshkova. Cosmonaut Alexei Leonov took the first spacewalk in 1965, and in 1966 astronauts Neil Armstrong and Dave Scott performed the first space-docking maneuver.