This is one of several full size replicas of the payload section and fourth stage booster of Explorer-1 in the collection. This replica has no internal parts. Explorer-1 was the first American satellite to successfully orbit the Earth. The launch of Sputnik-1 on October 4, 1957 and the launch failure of the Vanguard-1 satellite in December of that year seemed to symbolize America's failure to lead in the Space Race. Since the mid-1950's Caltech's Jet Propulsion Laboratory (JPL) had underway a development program for missile reentry vehicles in conjunction with the Army Ballistic Missile Agency (ABMA). Soon after the Vanguard failure the JPL- ABMA team was authorized to adapt the Jupiter-C reentry test vehicle to an instrumented earth satellite. The resulting Explorer-1 satellite was successfully launched and placed into Earth orbit on January 31, 1958. The satellite transmitted data on micrometeorites and cosmic radiation for 105 days. Data from this and two subsequent Explorer satellites led to the discovery by James Van Allen of a belt of intense radiation surounding the Earth.