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similar systems
Until 1985, the eleven ''Block I'' satellites were built. This number was increased until 1989 by the ''Block II'' satellites. GPS today uses 24 satellites and numerous ground stations.
Until 1985, the eleven ''Block I'' satellites were built. This number was increased until 1989 by the ''Block II'' satellites. GPS today uses 24 satellites and numerous ground stations.
==GPS Receivers==
==GPS receivers==
GPS receivers are an extremely fast and easy way to navigate. With the ability to tell you where you are, where you're heading, how to get there, and where just about anything else is they are tough to beat for convenience. It is easy to come to rely on GPS with all of its features and convenience, but it is important to remember that like any other electronic device it may fail. While the GPS network itself it very robust, requiring little more than regular corrections from ground based stations, GPS receivers are small relatively fragile devices than may break or run out of power.
GPS receivers are an extremely fast and easy way to navigate. With the ability to tell you where you are, where you're heading, how to get there, and where just about anything else is they are tough to beat for convenience. It is easy to come to rely on GPS with all of its features and convenience, but it is important to remember that like any other electronic device it may fail. While the GPS network itself it very robust, requiring little more than regular corrections from ground based stations, GPS receivers are small relatively fragile devices than may break or run out of power.
GPS receivers require that the clocks on the satellites be exquisitely well calibrated. The reason is that an error of 5 microseconds in the clock synchronization will lead to a position error of one mile. Achieving this accuracy requires that the clocks compensate for both the effects of [[special relativity]] (7 milliseconds per day) and [[general relativity]] (45 milliseconds per day in the opposite direction), leading to a total required correction of 38 milliseconds per day.<ref>http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html</ref>
GPS receivers require that the clocks on the satellites be exquisitely well calibrated. The reason is that an error of 5 microseconds in the clock synchronization will lead to a position error of one mile. Achieving this accuracy requires that the clocks compensate for both the effects of [[special relativity]] (7 milliseconds per day) and [[general relativity]] (45 milliseconds per day in the opposite direction), leading to a total required correction of 38 milliseconds per day.<ref>http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html</ref>
==Similar systems==
The Global Positioning System, developed and deployed by the united states, was the first of its kind. However, it was not the last. Only three years after the GPS program began, the Soviet Union began developing their own satellite positioning system, in 1976. They launched their first satellite on October 12, 1982, marking the beginning of ''Global’naya Navigatsionnaya Sputnikovaya Sistema'' (GLONASS). Due to deployment failures, short satellite lifespans, and funding issues, GLONASS has was not always fully operational. By 2002, GLONASS was down to seven of its needed twenty-four satellites. However, on December 8, 2011, the state of Russia successfully restored GLONASS to full operation. It has been mostly maintained since then.<ref>https://www.gpsworld.com/innovation-glonass-past-present-and-future/</ref>
Today, there are also other positioning systems in service, including:
*Galileo (European Union)
*BeiDou (China)
*Quasi-Zenith (also known as ''QZSS'' or ''Michibiki'', Japan's regional system of 4 satellites)
==See also==
==See also==