Image of Sputnik satellite. Courtesy of NASA/JPL

The Soviet Sputnik program consisted of four satellites, three of which reached Earth orbit.

Sputnik 1, launched on Oct.4, 1957, became the first artificial satellite to successfully orbit the Earth. It was a metallic sphere about 2 feet across, weighing 184 lbs (84 kg), with long "whiskers" pointing to one side, and stayed in orbit for 6 months before falling back to Earth. Its rocket booster, weighing 4 tons, also reached orbit and was easily visible from the ground.

The second Sputnik satellite was launched on Nov 3, 1957 and carried a dog, named Laika, into space. Biological data was returned for a week before the animal had to be put to sleep.

The Sputnik missions all happened during the midst of the Cold War between the U.S.S.R. and the United States. Americans became worried about the Soviet accomplishments and soon the development of space technology became a national priority.