The Satellite
Planning started for the Vanguard program in 1955. Both the launch vehicle and the satellite were to be named Vanguard, the only time that has happened in the U.S. space program. There were several "marks" of the satellite varying in size from 20 inches down to 6 inches in diameter with varying instrumentation on board and the first was slated to go up during the International Geophysical Year of 1958. The Martin Company developed the rocket and the Naval Research Laboratory developed the satellite.