Explorer 1 was the first satellite launched by the United States and was part of the U.S. participation in the International Geophysical Year. The mission followed the first two satellites the previous year; the Soviet Union's Sputnik 1 and 2, beginning the Cold War Space Race between the two nations.
Explorer 1 was launched on January 31, 1958 at 22:48 Eastern Time (February 1, 03:48 UTC) atop the first Juno booster from LC-26 at the Cape Canaveral Missile Annex in Florida. It was the first spacecraft to detect the Van Allen radiation belt, returning data until its batteries were exhausted after nearly four months. It remained in orbit until 1970 and was followed by more than ninety scientific spacecraft in the Explorer series.