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Satellite, Artificial

        Science | Astronomy Terms


When Isaac Newton published his law of gravitation in 1687 the basic information necessary to conceive of artificial satellites became available. Space travel became a favorite subject in science fiction, but the subject of artificial satellites was almost ignored until the mid-20th century.

In 1955 the United States and the Soviet Union both announced plans to put scientific satellites into orbit during the International Geophysical Year (IGY), 1957-58.

The first artificial satellite placed in orbit was the Soviet Union's Sputnik I, launched on October 4, 1957. The satellite, a 23-inch (58-cm) sphere weighing 184 pounds (83 kg), remained in orbit for three months; radio contact with it, however, was lost after 21 days.

Sputnik II was launched on November 3, 1957. It weighed 1,121 pounds (508 kg) and carried the first animal into orbita dog named Laika. Radio contact was maintained for a week, during which time much information was acquired about the animal's adjustment to the conditions of space.

The United States IGY effort was Project Vanguard, conducted by the U.S. Navy and designed to put a small sphere into orbit. On December 6, 1957, the first Vanguard launch failed.

While attempts were being made to correct the Vanguard launch system, Explorer I was orbited by the U.S. Army on January 31, 1958, using a Jupiter-C launch vehicle. Explorer I was a cylinder 80 inches (203 cm) long and 6 inches (15 cm) in diameter; it weighed 31 pounds (14 kg). Its orbit had a perigee of 224 miles (360 km) and an apogee of 1,584 miles (2,549 km). Through Explorer I scientists discovered that an area of radiation encircles the earth. Explorer I remained aloft for more than a decade.

The first successful Vanguard, weighing 3 pounds (1.36 kg), was launched in March, 1958. The Vanguard program, however, continued to have trouble; of 11 attempts to launch Vanguards, only 3 were successful.

During the rest of the 1950's, satellite launching remained a highly difficult endeavor. In 1958 and 1959, the United States attempted to put up 36 satellites, of which only 18 reached orbit. During the same period, the Soviet Union successfully launched three satellites.

With the 1960's came rapid improvement in launch techniques. The number of launches rapidly increased, as did the number of countries taking part in satellite programs. Reliability of launch systems so improved that by 1964 more than 90 per cent of the satellites launched achieved orbit. The number of launchings varied from year to year. In 1962, for example, the United States attempted to launch 58 satellites, of which 50 achieved orbit. During the same year, the Soviet Union announced 20 launchings; 3 of them failed to achieve orbit.

The first nations other than the Soviet Union and the United States to orbit satellites were Great Britain, Canada, Italy, France, Australia, Japan, and China. Of these, only France, Japan, and China orbited their first satellites completely on their own; the others used American launch vehicles.

On April 26, 1962, Ariel I, a satellite launched as part of a joint program by the United States and Great Britain, was placed in orbit to make X-ray studies in the ionosphere. In September of the same year, Alouette I, the first Canadian satellite, was placed in orbit at about 600 miles (965 km) altitude, also for ionospheric research.

Italy joined the nations having satellites in orbit on December 15, 1964, with a 254-pound (115-kg) satellite, called San Marco I, launched from Wallops Island. On November 26, 1965, France placed a 92-pound (42-kg) satellite, called AI, into an orbit with perigee of 328 miles (528 km) and apogee of 1,099 miles (1,769 km). Australia, in November of 1967, launched its first satellite, WRESAT I, from facilities near Woomera, Australia, using a modified Redstone rocket. Japan's first successful launching was in February, 1970, and China's in April.

In 1960, the United States began programs of applications satellites. Tiros 1, the first weather satellite, went into orbit on April 1, and Echo 1, the first communications satellite, orbited on August 12. Echo 1 was a 100-foot (30-m) balloon made of a thin plastic film coated with aluminum. Unlike the communications satellites in use today, Echo was a passive communications satellitethat is, it simply reflected the radio signals transmitted to it.

Also in 1960, Transit 1B, the U.S. Navy's first navigation satellite, was placed in orbit. A second navigation satellite, Transit 2A, was one of two satellites placed in orbit with a single Thor-Able-Star rocket on June 22 the first multiple launch. By 1965, multiple launches were common in both the American and the Soviet space programs, and in that year 61 satellites were orbited using 18 launch vehicles.

Telstar I, an American Telephone and Telegraph communications satellite, relayed the first live television broadcasts between Europe and the United States in 1962. Satellite transmission of regular commercial television became possible about three years later, when Early Bird, a satellite owned by the Communications Satellite Corporation, was placed in geosynchronous orbit over the Atlantic Ocean. Early Bird was the first geosynchronous communications satellite.

Artificial satellites have been in orbit around the sun since the beginning of 1959, when the first Soviet lunar probe passed the moon and continued in orbit around the sun. However, it was not until spring of 1966 that the first satellite was placed in lunar orbit. Luna 10, the first Soviet lunar satellite, was launched on March 31, 1966, followed by the American Lunar Orbiter 1, in August of the same year.

More than 700 satellites were placed in orbit in the first decade of space exploration, and by the 1970's satellite launchings had become commonplace. In the 1970's two major new types of satellite were launched space stations (the Soviet Salyut 1 in 1971 and the American Skylab in 1973) and satellites designed to provide data about the earth's surface and resources (beginning with the American Landsat series in 1972). Beginning in the 1980's American space shuttles were used to launch satellites from orbit. They were also used as a base from which to repair satellites in orbit and as a vehicle to return satellites to earth.

In the 1990's, important new satellite applications included the use of Global Positioning System satellites for civilian navigation and a variety of uses for communications, such as Direct Broadcast Satellite television and broadband Internet connections. In 2000, the International Space Station received its first crew.