Launched January 31, 1958
Reentered Earth“s atmosphere March 31, 1970

Spurred by the launch of the Soviet Union’s Sputnik satellite, the United States pursued two space programs simultaneously. The original project would produce Vanguard 1, but this satellite went into orbit several weeks after the success of Explorer 1.

U.S. space program initiated

Plans to send the first American satellite into space were announced on July 29, 1955, when “the launching of small unmanned Earth-circling satellites” was approved by President Dwight D. Eisenhower. The launch was to be part of the United States contribution to the International Geophysical Year (IGY) in 1958. (The IGY was a worldwide project in which scientists from 67 nations worked together to study the composition of the Sun as well as phenomena of Earth, such as the Northern Lights and deep ocean currents.) The first satellite development program, the Vanguard project, was plagued by problems from...