Tomorrow marks the 40th anniversary of the launch of Explorer 1, the first U.S. satellite to orbit the Earth. The 9-kilogram satellite was the U.S. response to the Soviet Union's Sputnik, which had been launched on 4 October 1957, touching off the Cold War space race between the two countries.
A month after Sputnik's flight, the government chose the Jet Propulsion Laboratory in Pasadena, California--then an Army research facility--to develop the first U.S. satellite. The successful launch 3 months later laid the groundwork for establishing a civilian space agency that in 1958 became NASA. Explorer 1 also had a scientific payoff: Its cosmic ray detector, designed by James Van Allen of the University of Iowa in Iowa City, led to the discovery of the so-called Van Allen Radiation Belts, two donut-shaped rings of intense radiation that girdle Earth along its magnetic field lines.