The First SatellitesJust after midnight (local time) on Oct. 5, 1957Ñthe late afternoon of October 4 in the eastern United
StatesÑthe Soviets launched Sputnik 1, an aluminum sphere 58 cm (23 in) in diameter and weighing 84 kg (184 lb). Not only did this achievement thrust a scientific challenge upon the United States, it also brought great political pressure to bear. After three successful development flights of the first stage of Vanguard, an attempt was made to launch the complete system, two months after the launch of Sputnik 1. Less than one second after lift-off, the first-stage engine lost thrust, and the vehicle settled back on the launch pad and exploded. The small
satellite, 15 cm (6 in) in diameter, continued to transmit signals as it lay on the pad.In the meantime, on Nov. 3, 1957, the Soviets had launched Sputnik 2, a much larger satellite than Sputnik 1, weighing 508 kg (1,121 lb). The satellite carried a live dog named Laika. Although the life-support materials aboard were only enough to keep the dog alive for a week, the
flight proved that animals could exist in a condition of weightlessness for an extended period of time. The flight was also a clear indication that the Soviet Union was embarking on a space program that would include human flight.The Soviet successes generated great domestic pressure for a strong U.S. space program. On November 8 the Army Ballistic Missile Agency (ABMA) in Huntsville, Ala., was asked to provide a backup to the Vanguard for launching an American satellite. The group, led by Wernher von Braun, had already converted a missile, the Redstone (see also rockets, missiles, and space launch vehicles), into the Jupiter C rocket for reentry tests by adding a spinning cluster of solid-propellant rockets arranged as three upper stages. This in turn was adapted as a satellite launcher, and on Jan. 31, 1958, the modified rocket, sometimes referred to as Juno 1, put the first American satellite into orbit. This payload, called Explorer 1, weighed 13.6 kg (30 lb) and carried instruments designed to measure cosmic rays, temperature, and micrometeorite collisions. It detected the Van Allen radiation belts. Not until March 1958 did the Vanguard launch a 1.8-kg (4-lb) satellite.