Sputnik, Russian for "fellow traveler of earth," was an unmanned Soviet satellite that orbited the earth on 4 October 1957. The kerosene-powered Sputnik weighed 84 kg (184 pounds), traveled at over 28,000 kilometers per hour (17,000 miles per hour) and continued to orbit until 4 January 1958. Although it did little more than transmit a monotonous beep, the successful orbit of the beachball-sized satellite became a seminal moment in the 20th century.
Since there are currently thousands of satellites orbiting in the skies above us, may be difficult to understand how earth-shattering Sputnik actually was. To begin to understand it's impact, we need to consider the context in which it existed. In 1955, the U.S. announced plans to create a satellite program that eventually became the Vanguard project. The progress of the Vanguard program, however, was slow and frustrating. Just as basic rocket testing was yielding some results, the world was informed about the Sputnik successfully orbiting the earth. The United States space program was in its infancy, and the Soviets had not only launched but achieved earth orbit!
Much of the impact was due to the secrecy; although some members of the intelligence community knew of the advanced status of a Soviet satellite program, the general public was caught completely off-guard. To most Americans, the thought that the Soviets could launch something in space that could fly over anywhere in the world, was terribly unsettling and frightening. The "beep, beep" of the Sputnik added greatly to the fear of nuclear war and created a response in America that bordered on panic. The space and arms races that consumed much of the second half of the 20th century can be traced back to the Sputnik.
Soviet progress in space continued after Sputnik I. On 3 November 1957 the Soviets launched Sputnik II carrying a test-dog named Laika. Sputnik III was launched in May 1958 and weighed almost 1,400 kilograms (3,000 pounds); it orbited for about two years and provided a wealth of information about the earth.