Sputnik is the name given to a series of scientific research satellites launched by the Soviet Union during the period from 1957 to 1961. The satellites ranged in size and capability from the 83.6-kilogram (184.3-pound) Sputnik 1, which served only as a limited radio transmitter, to Sputnik 10, which weighed 4,695 kilograms (10,350 pounds). Together the Sputnik flights ushered in the space age and began the exploration of space by orbital satellites and humans. Sputnik 1 is the most famous in the series.

In August 1957 the Soviet Union conducted a successful test flight of a stage-and-a-half liquid-fueled intercontinental ballistic missile called the R-7. Shortly thereafter Soviet scientists were quoted in the news media inside the Soviet Union saying that they were planning for the launch of an Earth satellite using a newly developed missile. Western observers scoffed at the accounts. In the late summer of 1957 Soviet scientists told a planning session of the International Geophysical...