On October 4, 1957, the Soviet Union launched the first artificial satellite, Sputnik 1. It was an aluminum sphere a bit less than 23 inches in diameter that weighed 183.9 pounds.
The Sputnik 1 satellite obtained data concerning the density of Earth's upper atmosphere and propagation of radio signals in the ionosphere. Data was transmitted from the satellite for three weeks, until the on-board batteries failed.
The launching of Sputnik 1 found the United States unprepared to compete. Not only was the U.S. not ready, the American satellite in development was much smaller than the Soviets', according to NASA. The launch of Sputnik 1 is considered the beginning of the space age.