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Global Positioning System: Difference between revisions
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The orbital planes are centered on the Earth, not rotating with respect to the distant stars.<ref>[http://metaresearch.org/cosmology/gps-relativity.asp What the Global Positioning System Tells Us about Relativity]. Accessed [[January 2]], [[2007]].</ref> The six planes have approximately 55° [[inclination]] (tilt relative to Earth's [[equator]]) and are separated by 60° [[right ascension]] of the [[orbital node|ascending node]] (angle along the equator from a reference point to the orbit's intersection).<ref name="GPS overview from JPO">[http://gps.losangeles.af.mil/jpo/gpsoverview.htm GPS Overview from the NAVSTAR Joint Program Office]. Accessed [[December 15]], [[2006]].</ref> | The orbital planes are centered on the Earth, not rotating with respect to the distant stars.<ref>[http://metaresearch.org/cosmology/gps-relativity.asp What the Global Positioning System Tells Us about Relativity]. Accessed [[January 2]], [[2007]].</ref> The six planes have approximately 55° [[inclination]] (tilt relative to Earth's [[equator]]) and are separated by 60° [[right ascension]] of the [[orbital node|ascending node]] (angle along the equator from a reference point to the orbit's intersection).<ref name="GPS overview from JPO">[http://gps.losangeles.af.mil/jpo/gpsoverview.htm GPS Overview from the NAVSTAR Joint Program Office]. Accessed [[December 15]], [[2006]].</ref> | ||
Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each | Orbiting at an altitude of approximately 20,200 kilometers (12,600 miles or 10,900 nautical miles; orbital radius of 26,600 km (16,500 mi or 14,400 NM)), each SV makes two complete orbits each sidereal day, so it passes over the same location on Earth once each day. The orbits are arranged so that at least six satellites are always within [[line of sight]] from almost anywhere on Earth.<ref>[http://www.navcen.uscg.gov/faq/gpsfaq.htm USCG Navcen: GPS Frequently Asked Questions]. Accessed [[January 3]], [[2007]].</ref> | ||
[[As of February 2007]], there are 30 actively broadcasting satellites in the GPS [[satellite constellation|constellation]]. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.<ref>Massatt, Paul and Brady, Wayne. "[http://www.aero.org/publications/crosslink/summer2002/index.html Optimizing performance through constellation management]", ''Crosslink'', Summer 2002, pages 17-21.</ref> | [[As of February 2007]], there are 30 actively broadcasting satellites in the GPS [[satellite constellation|constellation]]. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.<ref>Massatt, Paul and Brady, Wayne. "[http://www.aero.org/publications/crosslink/summer2002/index.html Optimizing performance through constellation management]", ''Crosslink'', Summer 2002, pages 17-21.</ref> | ||