any of a series of artificial Earth satellites whose launching by the Soviet Union beginning on October 4, 1957, inaugurated the space age. Sputnik 1, the first satellite launched by man, was a 184-pound (83.6-kg) capsule. It achieved an Earth orbit with an apogee (farthest point from Earth) of 584 miles (940 km) and a perigee (nearest point) of 143 miles (230 km), circling the Earth every 96 minutes and remaining in orbit until early 1958 when it fell back and burned in the Earth's atmosphere. Launched on November 3, 1957, Sputnik 2 carried the dog Laika, the first living creature to be shot into space and orbit the Earth. Eight more Sputnik missions with similar satellites carried out experiments on a variety of animals to test spacecraft life-support systems; they also tested reentry procedures and furnished data on space temperatures, pressures, particles, radiation, and magnetic fields.