GPS Facts
Some GPS trivia to impress your friends with
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Here is some GPS trivia for you to impress / alienate your friends with:
1. GPS started life as GPSS, or Global Positioning Satellite System, with the US military as a means of improving long range missile accuracy.
2. Because of its primary military use the American government still retain operational control of the system, and have the option to turn off the satellite signals at any time.
3. During the early public release of the technology from 1995 to 2000 the signal available for public use was deliberately downgraded to limit accuracy.
4. Since 2000, Selective Availability, as it was known, was turned off allowing a more uniform accuracy of around 15m.
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GALILEO, WAAS, EGNOS, GLONASS & MSAS
With the GPSS system still under the control of the USA, and susceptible to being turned off, new satellites and systems are being developed by other countries. These use a combination of geo-stationary satellites that orbit at the same velocity as the Earth’s rotation to maintain the same relative position and ground based relay stations.
These systems not only remove reliance on a single country, but also improve the accuracy to 3m horizontally and 4m vertically. Britain will eventually have this level of cover through the GALILEO satellite system scheduled to be fully operational in 2010 as part of the European Geostationary Navigation Overlay Service (better known as EGNOS). Similar augmentation systems will be available to cover the USA (WAAS) Russia (GLONASS) and Asis/Pacific (MSAS). These systems have an average accuracy of around 95%, but this is dependent on the available line of sight to sufficient satellites.
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A picture of a navigation satellite
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GPS Basics
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Getting Started
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GPS Buyer's Guide
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Using Your GPS
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GPS and Your PC
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Discuss this story
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