- vanguard
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/van"gahrd'/, n.1. the foremost division or the front part of an army; advance guard; van.2. the forefront in any movement, field, activity, or the like.3. the leaders of any intellectual or political movement.4. (cap.) Rocketry. a U.S. three-stage, satellite-launching rocket, the first two stages powered by liquid-propellant engines and the third by a solid-propellant engine.
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Any of three unmanned U.S. experimental satellites.Vanguard I (1958), the second U.S. satellite placed in orbit around Earth (after Explorer 1), was a tiny 3.25-lb (1.47-kg) sphere with two radio transmitters. Its flight path revealed that Earth is almost imperceptibly pear-shaped, confirming earlier theories. Vanguard II (1959) carried light-sensitive photocells to provide information about Earth's cloud cover, but its tumbling motion rendered the data unreadable. Vanguard III (1959) was used to map Earth's magnetic field.* * *
any of a series of unmanned U.S. experimental test satellites. Vanguard I, launched March 17, 1958, consisted of a tiny 3.25-pound (1.47-kilogram) sphere equipped with two radio transmitters. It was the second artificial satellite placed in orbit around the Earth by the United States, the first being Explorer 1 (Jan. 31, 1958). By monitoring Vanguard's flight path, scientists found that the Earth was almost imperceptibly pear-shaped, in confirmation of earlier theories. Vanguard II, orbited on Feb. 17, 1959, carried light-sensitive photocells that were designed to provide information about the Earth's cloud cover, but the tumbling motion of the satellite rendered the data unreadable. Vanguard III, the last in the series, was launched several months later. It was used to map the Earth's magnetic field.* * *
Universalium. 2010.