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'''Global Positioning System''' ('''GPS''') is a [[United States]] [[satellite]] system that lets those on the ground, on the water or in the air determine their position with extreme accuracy based on timing signals sent from satellites. You triangulate your position through the use of a GPS receiver.

'''Global Positioning System''' ('''GPS''') is a [[United States]] [[satellite]] system that lets those on the ground, on the water or in the air determine their position with extreme accuracy based on timing signals sent from satellites. You triangulate your position through the use of a GPS receiver.

The system was developed by the US [[Department of Defense]] and made available to the general public in 1983 under orders of [[Ronald Reagan | President Reagan]]. GPS for civilian use used to include a mechanism called Selective Availability that intentionally limited the accuracy of GPS, a mechanism originally intended to confuse potential enemies who might launch a missile attack, but Selective Availability was disabled in 2000, and appears unlikely to be reinstated in the foreseeable future.

The system was developed by the US [[Department of Defense]] and made available to the general public in 1983 under orders of [[Ronald Reagan|President Reagan]]. GPS for civilian use used to include a mechanism called Selective Availability that intentionally limited the accuracy of GPS, a mechanism originally intended to confuse potential enemies who might launch a missile attack, but Selective Availability was disabled in 2000, and appears unlikely to be reinstated in the foreseeable future.

Prosecutors are now using data from GPS units to convict criminals. Authorities can analyse data from the GPS units to establish a defendant's whereabouts or to track suspects. <ref>[http://www.foxnews.com/story/0,2933,413041,00.html Small GPS Devices Help Prosecutors Win Convictions], Associated Press, ''Fox News'', August 28, 2008</ref>

Prosecutors are now using data from GPS units to convict criminals. Authorities can analyse data from the GPS units to establish a defendant's whereabouts or to track suspects.<ref>[http://www.foxnews.com/story/0,2933,413041,00.html Small GPS Devices Help Prosecutors Win Convictions], Associated Press, ''Fox News'', August 28, 2008</ref>

== History ==

== History ==

In 1968 the [[Department of Defense]] coordinated these efforts by creating a tri-service committee - the ''navigation Satellite Executive Group'' (''NAVSEG''): the technologies of ''System 621B'' and ''Timation'' were combined under the name '''NAVSTAR GPS''' - and the last two satellites of the ''Timation'' program became the first ''NAVSTAR'' satellites: [[NTS-1]]<ref>[http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1978-020A National Space Science Data Center] 1978-020A</ref> (Feb 22, 1978) and [[NTS-2]]<ref>[http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1978-047A National Space Science Data Center] 1978-047A</ref> (May 13, 1978).

In 1968 the [[Department of Defense]] coordinated these efforts by creating a tri-service committee - the ''navigation Satellite Executive Group'' (''NAVSEG''): the technologies of ''System 621B'' and ''Timation'' were combined under the name '''NAVSTAR GPS''' - and the last two satellites of the ''Timation'' program became the first ''NAVSTAR'' satellites: [[NTS-1]]<ref>[http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1978-020A National Space Science Data Center] 1978-020A</ref> (Feb 22, 1978) and [[NTS-2]]<ref>[http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1978-047A National Space Science Data Center] 1978-047A</ref> (May 13, 1978).

In 1978, the Naval Research Lab in Washington published its report on the [http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA058591 Initial Results of the NAVSTAR GPS NTS-2 Satellite]<ref>[http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA058591 Initial Results of the NAVSTAR GPS NTS-2 Satellite], Naval Research Lab Washington, D.C.,  25 May 1978 (Full text: [http://www.leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf pdf])</ref>. It listed the following ''GPS objectives that have been achieved to date'':

In 1978, the Naval Research Lab in Washington published its report on the [http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA058591 Initial Results of the NAVSTAR GPS NTS-2 Satellite].<ref>[http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA058591 Initial Results of the NAVSTAR GPS NTS-2 Satellite], Naval Research Lab Washington, D.C.,  25 May 1978 (Full text: [http://www.leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf pdf])</ref> It listed the following ''GPS objectives that have been achieved to date'':

#launch  insertion  into  GPS  constellation  position

#launch  insertion  into  GPS  constellation  position

#demonstrated  orbit  stability  and  controllability

#demonstrated  orbit  stability  and  controllability

That is why [[maps]] and [[compass]] are two of the two most essential pieces of navigation gear that one should carry. GPS devices and [[cell phone]]s with [[Google]] maps may breakdown or run out of [[battery|batteries]] during an [[emergency]], [[disaster]] or a [[Post Apocalyptic World]] - [[SHTF]] - [[TEOTWAWKI]] event. Also the sun isn't always shining, and it takes a great deal of time and effort to learn to stellar navigation, however a map and compass will continue to work until your break or lose them.

That is why [[maps]] and [[compass]] are two of the two most essential pieces of navigation gear that one should carry. GPS devices and [[cell phone]]s with [[Google]] maps may breakdown or run out of [[battery|batteries]] during an [[emergency]], [[disaster]] or a [[Post Apocalyptic World]] - [[SHTF]] - [[TEOTWAWKI]] event. Also the sun isn't always shining, and it takes a great deal of time and effort to learn to stellar navigation, however a map and compass will continue to work until your break or lose them.

==See Also==

==See also==

* [[GPS]], [[Map]] and [[Compass]] for [[Navigation]]

* [[GPS]], [[Map]] and [[Compass]] for [[Navigation]]

* [[Orienteering]]

* [[Orienteering]]

* [http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-540-principles-of-the-global-positioning-system-spring-2012/ Global Positioning System] Open Courseware from [[MIT]], 2012

* [http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-540-principles-of-the-global-positioning-system-spring-2012/ Global Positioning System] Open Courseware from [[MIT]], 2012

==External Links==

==External links==

* [http://code8100.nrl.navy.mil/about/heritage/nts.htm Timation],  U.S. Naval Research Laboratory, Space Systems Development Department (SSDD)

* [http://code8100.nrl.navy.mil/about/heritage/nts.htm Timation],  U.S. Naval Research Laboratory, Space Systems Development Department (SSDD)

* [http://pnt.gov/101/gps.html The Global Positioning System], Space-Based Positioning Navigation & Timing, National Executive Comittee

* [http://pnt.gov/101/gps.html The Global Positioning System], Space-Based Positioning Navigation & Timing, National Executive Comittee