This miniaturized tape recorder is a flight spare (backup) for one that flew on Explorer 3, launched on 26 March 1958. Data were saved on tape until they could be transmitted to a ground station that could accept telemetry data. These data included measurements of the distribution of cosmic ray intensity, micrometeorites, and temperature and they confirmed the existence of the Van Allen Radiation Belt, a huge area of charged particles that circles the earth. This first tape recorder to be flown on a satellite was designed and built by the Department of Physics at the University of Iowa under James Van Allen's supervision. He donated the flight spare to the Smithsonian Institution in 1968 along with a presentation mounting and provenance. It was refurbished at the University of Iowa in 1981 and was returned to the collection in 1982.