Launch of Explorer 1

On 31 January 1958, the US successfully launched its first satellite, Explorer 1. The mission was technically part of the country’s participation in the International Geophysical Year , but the stakes had been raised after the Soviet Union launched Sputnik 1 and Sputnik 2 in 1957 to take an early lead in the space race. Anxious to match the Soviets’ feat, the US Army Ballistic Missile Agency quickly prepared its Jupiter C rocket for a satellite launch; the Jet Propulsion Laboratory built the 200-cm-long satellite in less than three months. The much-anticipated launch took place at 10:48pm EST on 31 January. Explorer 1 successfully entered Earth orbit and made more than 58 000 revolutions before it burned up in the atmosphere on 31 March 1970. The satellite carried scientific instruments, including a cosmic-ray detector whose measurements led to the discovery of the Van Allen radiation belts . (Photo credit: NASA)

Date in History: 31 January 1958