With Sputnik, the “beep heard all over the world,” the Soviets launched both the first space satellite and the space race with the United States. Carried aboard a Vostok-K rocket, Sputnik taught scientists about the density of the atmosphere in low Earth orbit, as well as information on the ionosphere. Sputnik was a polished sphere, 23 inches (58 centimeters) in diameter, with four external radio antennas to transmit radio pulses. It sent radio signals for 22 days and orbited the Earth for three months after the October 4, 1957 launch. The Americans reacted to Sputnik with curiosity and fear, and this historical event accelerated the development of American space technology. One of the models used in the tests is displayed here.