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Global Positioning System (view source)
Revision as of 23:24, January 27, 2010
, 23:24, January 27, 2010History (new section)
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 ==
When the [[Soviet Union]] launched the [[satellite]] [[Sputnik]] in 1957, American scientists of the [[Johns Hopkins University]] [[Applied Physics Laboratory]] used ''Sputnik's'' [[radio]]-signal's [[Doppler Effect]] to track its position. They realized that a similar procedure for satellites with well known orbits would allow to calculate an unknown position on earth, and so the idea for the '''Transit''' was born: the first operational satellite-based navigation system. It consisted from seven low-altitude polar-orbiting satellites, and one of its main purposes was to provide navigation data for the [Submarine|Polaris missile submarine]]s. Though it had a couple of disadvantages, the ''Transit'' system was in use until 1996.
Another project was [[United States Air Force]]'s '''System 621B''', which - other than ''Transit'' - allowed for three-dimensional navigation. The [[United States Army|army]] had its own project: '''Army-SECO''', while [[United States Navy|navy]]'s '''Timation''' program used the most accurate clocks, deploying its first satellite in 1967 with [[quartz]]-[[crystal]] [[oscillator]]s, but developing [[atomic clock]]s for its last two satellites.
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'':
#launch insertion into GPS constellation position
#demonstrated orbit stability and controllability
#first cesium frequency standard in space
#verification of relativity theory
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.
==External Links==
*[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://mms.nps.gov/gis/gps/How_GPS_Works.ppt An Introduction to the Global Positioning System], Charlie Leonard, 1999 (revised 2001, 2002), PowerPointPresentation
==References==
==References==