Flight spare radio transmitter for the Explorer 1 satellite built at the Jet Propulsion Laboratory (JPL) in late 1957. After the transmitter was discarded by JPL it was refurbished over 1993-1996 by Henry L. Richter, formerly head of the group that developed Explorer 1 systems. Richter donated this object to NASM and shipped it 1997.

Explorer-1, also known unofficially as Satellite 1958 alpha, was the first American satellite to successfully orbit the Earth. Since the mid-1950's Caltech's JPL had underway a development program for missile reentry vehicles in conjunction with the Army Ballistic Missile Agency (ABMA). Soon after the Vanguard explosion the JPL- ABMA team were authorized to adapt the Jupiter-C reentry test vehicle to launch 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 surrounding the Earth.