08 May 2009

Communications satellite

The invention: Telstar I, the world’s first commercial communications satellite, opened the age of live, worldwide television by connecting the United States and Europe. The people behind the invention: Arthur C. Clarke (1917- ), a British science-fiction writer who in 1945 first proposed the idea of using satellites as communications relays John R. Pierce (1910- ), an American engineer who worked on the Echo and Telstar satellite communications projects Science Fiction? In 1945, Arthur C. Clarke suggested that a satellite orbiting high above the earth could relay television signals between different stations on the ground, making for a much wider range of transmission than that of the usual ground-based systems. Writing in the February, 1945, issue of Wireless World, Clarke said that satellites “could give television and microwave coverage to the entire planet.” In 1956, John R. Pierce at the Bell Telephone Laboratories of the American Telephone & Telegraph Company (AT&T) began to urge the development of communications satellites. He saw these satellites as a replacement for the ocean-bottom cables then being used to carry transatlantic telephone calls. In 1950, about one-and-a-half million transatlantic calls were made, and that number was expected to grow to three million by 1960, straining the capacity of the existing cables; in 1970, twenty-one million calls were made. Communications satellites offered a good, cost-effective alternative to building more transatlantic telephone cables. On January 19, 1961, the Federal Communications Commission (FCC) gave permission for AT&T to begin Project Telstar, the first commercial communications satellite bridging the Atlantic Ocean.AT&T reached an agreement with the National Aeronautics and Space Administration (NASA) in July, 1961, in which AT&T would pay $3 million for each Telstar launch. The Telstar project involved about four hundred scientists, engineers, and technicians at the Bell Telephone Laboratories, twenty more technical personnel at AT&T headquarters, and the efforts of more than eight hundred other companies that provided equipment or services. Telstar 1 was shaped like a faceted sphere, was 88 centimeters in diameter, and weighed 80 kilograms. Most of its exterior surface (sixty of the seventy-four facets) was covered by 3,600 solar cells to convert sunlight into 15 watts of electricity to power the satellite. Each solar cell was covered with artificial sapphire to reduce the damage caused by radiation. The main instrument was a two-way radio able to handle six hundred telephone calls at a time or one television channel. The signal that the radio would send back to Earth was very weak—less than one-thirtieth the energy used by a household light bulb. Large ground antennas were needed to receive Telstar’s faint signal. The main ground station was built by AT&T in Andover, Maine, on a hilltop informally called “Space Hill.” A horn-shaped antenna, weighing 380 tons, with a length of 54 meters and an open end with an area of 1,097 square meters, was mounted so that it could rotate to track Telstar across the sky. To protect it from wind and weather, the antenna was built inside an inflated dome, 64 meters in diameter and 49 meters tall. It was, at the time, the largest inflatable structure ever built. A second, smaller horn antenna in Holmdel, New Jersey, was also used.International Cooperation In February, 1961, the governments of the United States and England agreed to let the British Post Office and NASAwork together to test experimental communications satellites. The British Post Office built a 26-meter-diameter steerable dish antenna of its own design at Goonhilly Downs, near Cornwall, England. Under a similar agreement, the French National Center for Telecommunications Studies constructed a ground station, almost identical to the Andover station, at Pleumeur-Bodou, Brittany, France. After testing, Telstar 1 was moved to Cape Canaveral, Florida, and attached to the Thor-Delta launch vehicle built by the Douglas Aircraft Company. The Thor-Delta was launched at 3:35 a.m. eastern standard time (EST) on July 10, 1962. Once in orbit, Telstar 1 took 157.8 minutes to circle the globe. The satellite came within range of the Andover station on its sixth orbit, and a television test pattern was transmitted to the satellite at 6:26 p.m. EST. At 6:30 p.m. EST, a tape-recorded black-and-white image of the American flag with the Andover station in the background, transmitted from Andover to Holmdel, opened the first television show ever broadcast by satellite. Live pictures of U.S. vice president Lyndon B. Johnson and other officials gathered at Carnegie Institution inWashington, D.C., followed on the AT&T program carried live on all three American networks. Up to the moment of launch, it was uncertain if the French station would be completed in time to participate in the initial test. At 6:47 p.m. EST, however, Telstar’s signal was picked up by the station in Pleumeur-Bodou, and Johnson’s image became the first television transmission to cross the Atlantic. Pictures received at the French station were reported to be so clear that they looked like they had been sent from only forty kilometers away. Because of technical difficulties, the English station was unable to receive a clear signal. The first formal exchange of programming between the United States and Europe occurred on July 23, 1962. This special eighteenminute program, produced by the European Broadcasting Union, consisted of live scenes from major cities throughout Europe and was transmitted from Goonhilly Downs, where the technical difficulties had been corrected, to Andover via Telstar. On the previous orbit, a program entitled “America, July 23, 1962,” showing scenes from fifty television cameras around the United States, was beamed from Andover to Pleumeur-Bodou and seen by an estimated one hundred million viewers throughout Europe.Consequences Telstar 1 and the communications satellites that followed it revolutionized the television news and sports industries. Before, television networks had to ship film across the oceans, meaning delays of hours or days between the time an event occurred and the broadcast of pictures of that event on television on another continent. Now, news of major significance, as well as sporting events, can be viewed live around the world. The impact on international relations also was significant, with world opinion becoming able to influence the actions of governments and individuals, since those actions could be seen around the world as the events were still in progress. More powerful launch vehicles allowed new satellites to be placed in geosynchronous orbits, circling the earth at a speed the same as the earth’s rotation rate. When viewed from the ground, these satellites appeared to remain stationary in the sky. This allowed continuous communications and greatly simplified the ground antenna system. By the late 1970’s, private individuals had built small antennas in their backyards to receive television signals directly from the satellites.


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