Allen radiation belt by the Explorer satellites was considered to be one of the outstanding discoveries of the International Geophysical Year (IGY). Explorer 3 was placed in an orbit with a perigee of and an apogee of having a period of 115.70 minutes, and inclination of 33.38°. Its total weight was , of which was instrumentation. The instrument section at the front end of the satellite and the empty scaled-down fourth-stage rocket casing orbited as a single unit, spinning around its long axis at 750 revolutions per minute. Data from these instruments was transmitted to the ground by a 60 milliwatt transmitter operating on 108.03 MHz and a 10 milliwatt transmitter operating on 108.00 MHz. Transmitting antennas consisted of two fiberglass slot antennas in the body of the satellite itself. The four flexible whip antennas of Explorer 1 were removed from the design. The external skin of the instrument section was painted in alternate strips of white and dark green to provide passive temperature control of the satellite. The proportions of the light and dark strips were determined by studies of shadow-sunlight intervals based on firing time, trajectory, orbit, and orbital inclination. Electrical power was provided by Mallory type RM Mercury batteries that made up approximately 40% of the payload weight. These provided power that operated the high power transmitter for 31 days and the low-power transmitter for 105 days. Because of the limited space available and the requirements for low weight, the Explorer 3 instrumentation was designed and built with simplicity and high reliability in mind. It was completely successful. Explorer 3 decayed from orbit on 28 June 1958, after 93 days of operation. A replica of the spacecraft is currently located in the Smithsonian Institution's National Air and Space Museum, Milestones of Flight Gallery. See also Timeline of artificial satellites and space probes Explorer program References External links Data Sheet, Department of Astronautics, National Air and Space Museum, Smithsonian Institution. Spacecraft launched in 1958 Spacecraft which reentered in 1958 Explorers Program 1958 in the United States