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Communications Satellites
| Article
# : |
12665 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1987 |
3,545 Words |
| Author
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Charles Sheffield
Charles Sheffield is the author of several science fiction
novels as well as numerous articles and essays on physics and
space science. |
Some must work while others play. As half the world relaxes at home, watching the Olympic Games live on television, a Manhattan bank clerk waits for two final entries before his books can be closed. One is a yen account, being transferred from Tokyo. The other, in pounds sterling, is arriving from London. Both transfers are half an hour late, and the bank clerk is itching to leave.
Two thousand miles to the northwest, an airborne rescue team has finally spotted a missing aircraft amid the stunted tundra of northern Manitoba, and is looking for a place to land. The approximate location was pinpointed an hour ago. Now the message has already gone back to base that the downed crew is alive and apparently uninjured.
Meanwhile, on the other side of the world, morning language classes go on in a schoolroom of rural India. For the first time, the villagers are learning a common tongue, one that will be understood across their whole nation.
It is no surprise that these activities all go on simultaneously; nor is it surprising that each of them could not be accomplished without modern technology. What is astonishing is that each depends on a single development: the communications satellite, a marriage of communications and space technology that celebrates its silver anniversary this year. Telstar, the world's first commercial communications satellite, was launched twenty-five years ago, on July 10, 1962.
Principles Outlined
The first crude attempts to communicate via satellite were conducted in 1958 and 1960, near the beginning of the U.S. space program. However, the basic ideas can be traced back a lot farther than that. In May 1945, an English scientist typed a four-page memorandum on the possible use of space-based facilities for radio and television services. He sent the half dozen copies, which was all the carbons that his typewriter would produce, to friends. In that note, Arthur C. Clarke set forth all the basic principles behind today's communications satellites. A later paper, published in Wireless World in October 1945 under the title "Extraterrestrial Relays," gave additional technical details.
Clarke was motivated to consider orbiting systems for radio and television by one well-known physical fact: Radio and television waves travel, like light waves, in straight lines. Thus a transmitter at the top of a radio tower sends a signal
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