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.

04 May 2009

Colossus computer

The invention: The first all-electronic calculating device, the Colossus computer was built to decipher German military codes during World War II. The people behind the invention: Thomas H. Flowers, an electronics expert Max H. A. Newman (1897-1984), a mathematician Alan Mathison Turing (1912-1954), a mathematician C. E. Wynn-Williams, a member of the Telecommunications Research Establishment An Undercover Operation In 1939, during World War II (1939-1945), a team of scientists, mathematicians, and engineers met at Bletchley Park, outside London, to discuss the development of machines that would break the secret code used in Nazi military communications. The Germans were using a machine called “Enigma” to communicate in code between headquarters and field units. Polish scientists, however, had been able to examine a German Enigma and between 1928 and 1938 were able to break the codes by using electromechanical codebreaking machines called “bombas.” In 1938, the Germans made the Enigma more complicated, and the Polish were no longer able to break the codes. In 1939, the Polish machines and codebreaking knowledge passed to the British. Alan Mathison Turing was one of the mathematicians gathered at Bletchley Park to work on codebreaking machines. Turing was one of the first people to conceive of the universality of digital computers. He first mentioned the “Turing machine” in 1936 in an article published in the Proceedings of the London Mathematical Society. The Turing machine, a hypothetical device that can solve any problem that involves mathematical computation, is not restricted to only one task—hence the universality feature. Turing suggested an improvement to the Bletchley codebreaking machine, the “Bombe,” which had been modeled on the Polish bomba. This improvement increased the computing power of the machine. The new codebreaking machine replaced the tedious method of decoding by hand, which in addition to being slow, was ineffective in dealing with complicated encryptions that were changed daily. Building a Better Mousetrap The Bombe was very useful. In 1942, when the Germans started using a more sophisticated cipher machine known as the “Fish,” Max H. A. Newman, who was in charge of one subunit at Bletchley Park, believed that an automated device could be designed to break the codes produced by the Fish. Thomas H. Flowers, who was in charge of a switching group at the Post Office Research Station at Dollis Hill, had been approached to build a special-purpose electromechanical device for Bletchley Park in 1941. The device was not useful, and Flowers was assigned to other problems. Flowers began to work closely with Turing, Newman, and C. E. Wynn-Williams of the Telecommunications Research Establishment (TRE) to develop a machine that could break the Fish codes. The Dollis Hill team worked on the tape driving and reading problems, and Wynn-Williams’s team at TRE worked on electronic counters and the necessary circuitry. Their efforts produced the “Heath Robinson,” which could read two thousand characters per second. The Heath Robinson used vacuum tubes, an uncommon component in the early 1940’s. The vacuum tubes performed more reliably and rapidly than the relays that had been used for counters. Heath Robinson and the companion machines proved that high-speed electronic devices could successfully do cryptoanalytic work (solve decoding problems). Entirely automatic in operation once started, the Heath Robinson was put together at Bletchley Park in the spring of 1943. The Heath Robinson became obsolete for codebreaking shortly after it was put into use, so work began on a bigger, faster, and more powerful machine: the Colossus. Flowers led the team that designed and built the Colossus in eleven months at Dollis Hill. The first Colossus (Mark I) was a bigger, faster version of the Heath Robinson and read about five thousand characters per second. Colossus had approximately fifteen hundred vacuum tubes, which was the largest number that had ever been used at that time. Although Turing and Wynn-Williams were not directly involved with the design of the Colossus, their previous work on the Heath Robinson was crucial to the project, since the first Colossus was based on the Heath Robinson. Colossus became operational at Bletchley Park in December, 1943, and Flowers made arrangements for the manufacture of its components in case other machines were required. The request for additional machines came in March, 1944. The second Colossus, the Mark II, was extensively redesigned and was able to read twentyfive thousand characters per second because it was capable of performing parallel operations (carrying out several different operations at once, instead of one at a time); it also had a short-term memory. The Mark II went into operation on June 1, 1944. More machines were made, each with further modifications, until there were ten. The Colossus machines were special-purpose, programcontrolled electronic digital computers, the only known electronic programmable computers in existence in 1944. The use of electronics allowed for a tremendous increase in the internal speed of the machine. Impact The Colossus machines gave Britain the best codebreaking machines of World War II and provided information that was crucial for the Allied victory. The information decoded by Colossus, the actual messages, and their influence on military decisions would remain classified for decades after the war. The later work of several of the people involved with the Bletchley Park projects was important in British computer development after the war. Newman’s and Turing’s postwar careers were closely tied to emerging computer advances. Newman, who was interested in the impact of computers on mathematics, received a grant from the Royal Society in 1946 to establish a calculating machine laboratory at Manchester University. He was also involved with postwar computer growth in Britain. Several other members of the Bletchley Park team, including Turing, joined Newman at Manchester in 1948. Before going to Manchester University, however, Turing joined Britain’s National Physical Laboratory (NPL). At NPL, Turing worked on an advanced computer known as the Pilot Automatic Computing Engine (Pilot ACE). While at NPL, Turing proposed the concept of a stored program, which was a controversial but extremely important idea in computing. A“stored” program is one that remains in residence inside the computer, making it possible for a particular program and data to be fed through an input device simultaneously. (The Heath Robinson and Colossus machines were limited by utilizing separate input tapes, one for the program and one for the data to be analyzed.) Turing was among the first to explain the stored-program concept in print. He was also among the first to imagine how subroutines could be included in a program. (Asubroutine allows separate tasks within a large program to be done in distinct modules; in effect, it is a detour within a program. After the completion of the subroutine, the main program takes control again.)