Launch Vehicle: Vanguard TV (Test Vehicle) and SLV (Satellite Launch Vehicle)
First Launch: 6 December 1957
Total Weight: 3.25 pounds
Diameter: 6 inches
Systems: Two radio transmitters

Begun by the US Navy in 1955 in an era of bitter interservice rivalry, the Vanguard program was an attempt to place the first artificial earth-orbit satellite in space. As it turned out, the Soviet Union's Sputnik 1 and the US Army's Explorer 1 both preceded Vanguard 1 into orbit. The program included both a Vanguard launch vehicle and a Vanguard spacecraft. Like the Army-initiated Explorer satellites of the same era, the Vanguard spacecraft were generally dissimilar scientific spacecraft. They were all spherical, but their instrumentation varied, as did their size. The first three Vanguards were only 6 inches in diameter, while most of the later Vanguards were 20 inches. The ninth consisted of two spheres, 13 and 30 inches in diameter.

The Vanguard launch vehicle was based on a Viking first stage, Aerobee second stage, and a specially designed third stage. The launch vehicles were given the designations TV (test vehicle) and SLV (satellite launch vehicle) to distinguish the test and operational vehicles. The first two test vehicle launches, which did not carry spacecraft, were successful, but of the 11 that followed (all carrying spacecraft) only three succeeded in placing a spacecraft into orbit. This 27 percent success rate gave the Vanguard the worst record of any US launch vehicle.

The first two Vanguard test vehicle launches (TV-1 and TV-2) took place on 1 May 1957 and 23 October 1957. These successful launches were followed by two test vehicle launches (TV-3 and TV-3 backup) carrying spacecraft. In both of these tests, however, the launch vehicles went off course and the spacecraft did not go into orbit. Had these launches been successful, the spacecraft would have been designated Vanguard 1 and Vanguard 2. The third spacecraft to be launched was successful and it was designated Vanguard 1. In the Vanguard program only the three successfully orbited spacecraft were given designations.

The first Vanguard launches and the first seven Vanguard spacecraft (including Vanguard 1) were under the management of the Naval Research Laboratories, after which the responsibility for the project was transferred to NASA.