Editing Global Positioning System (section)

== Overview ==
The GPS project was started by the [[United States Department of Defense|U.S. Department of Defense]] in 1973.<ref name=":1">{{Cite book |last=Lee |first=Eunsu |url=https://books.google.com/books?id=0A9vEAAAQBAJ&newbks=0&printsec=frontcover&pg=PA3&dq=The+GPS+project+was+started+by+the+U.S.+Department+of+Defense+in+1973.&hl=vi&source=newbks_fb&redir_esc=y#v=onepage&q=The%20GPS%20project%20was%20started%20by%20the%20U.S.%20Department%20of%20Defense%20in%201973.&f=false |title=Geographic Information Systems for Intermodal Transportation: Methods, Models, and Applications |date=March 21, 2023 |publisher=Elsevier |isbn=978-0-323-90130-7 |pages=3 |language=en}}</ref> The first prototype spacecraft was launched in 1978 and the full constellation of 24 satellites became operational in 1993.<ref name=":1" /> After [[Korean Air Lines Flight 007]] was shot down when it mistakenly entered Soviet airspace, President [[Ronald Reagan]] determined that the GPS system would be made available for civilian use as of 1988;<ref name=":2">{{Cite web |title=Statement by Deputy Press Secretary Speakes on the Soviet Attack on a Korean Civilian Airliner {{!}} Ronald Reagan |url=https://www.reaganlibrary.gov/archives/speech/statement-deputy-press-secretary-speakes-soviet-attack-korean-civilian-airliner-1 |access-date=2025-05-27 |website=www.reaganlibrary.gov |language=en}}</ref> however, initially this civilian use was limited to an average accuracy of {{convert|100|m|spell=us}} by use of [[Selective Availability]] (SA), a deliberate error introduced into the GPS data that military receivers could correct for.

As civilian GPS usage grew, there was increasing pressure to remove this error. The SA system was temporarily disabled during the [[Gulf War]], as a shortage of military GPS units meant that many US soldiers were using civilian GPS units sent from home. In the 1990s, [[Differential GPS]] systems from the [[US Coast Guard]], [[Federal Aviation Administration]], and similar agencies in other countries began to broadcast local GPS corrections, reducing the effect of both SA degradation and atmospheric effects (that military receivers also corrected for). The U.S. military had also developed methods to perform local GPS jamming, meaning that the ability to globally degrade the system was no longer necessary. As a result, United States President [[Bill Clinton]] signed a bill ordering that Selective Availability be disabled on May 1, 2000;<ref name="gpsgovaccurary">{{cite web |author1=((National Coordination Office for Space-Based Positioning, Navigation, and Timing)) |date=March 3, 2022 |title=GPS Accuracy |url=https://www.gps.gov/systems/gps/performance/accuracy/ |url-status=live |archive-url=https://web.archive.org/web/20220412092629/https://www.gps.gov/systems/gps/performance/accuracy/ |archive-date=April 12, 2022 |access-date=April 12, 2022 |website=GPS.gov}}</ref> and, in 2007, the US government announced that the next generation of GPS satellites would not include the feature at all.

Advances in technology and new demands on the existing system have now led to efforts to modernize the GPS and implement the next generation of [[GPS Block III]] satellites and Next Generation Operational Control System (OCX)<ref name="losangelesmil">{{cite web|url=https://www.losangeles.spaceforce.mil/?id=18676 |title=Factsheets: GPS Advanced Control Segment (OCX) |publisher=Losangeles.af.mil |date=October 25, 2011 |access-date=November 6, 2011 |url-status=live |archive-url=https://web.archive.org/web/20120503181621/http://www.losangeles.af.mil/library/factsheets/factsheet.asp?id=18676 |archive-date=May 3, 2012 }}</ref> which was authorized by the [[United States Congress|U.S. Congress]] in 2000. When Selective Availability was discontinued, GPS was accurate to about {{convert |5 |m |spell=us}}. GPS receivers that use the L5 band have much higher accuracy of {{convert|30|cm|sp=us|0|}}, while those for high-end applications such as engineering and land surveying are accurate to within {{convert|2|cm|abbr=on|frac=4}} and can even provide sub-millimeter accuracy with long-term measurements.<ref name="gpsgovaccurary" /><ref>{{Cite news|url=https://www.theverge.com/circuitbreaker/2017/9/25/16362296/gps-accuracy-improving-one-foot-broadcom|title=GPS will be accurate within one foot in some phones next year|work=The Verge|access-date=January 17, 2018|archive-url=https://web.archive.org/web/20180118113646/https://www.theverge.com/circuitbreaker/2017/9/25/16362296/gps-accuracy-improving-one-foot-broadcom|archive-date=January 18, 2018|url-status=live |last1=Kastrenakes |first1=Jacob |date=September 25, 2017 }}</ref><ref>{{cite news |last1=Moore |first1=Samuel K. |title=Superaccurate GPS Chips Coming to Smartphones in 2018 |url=https://spectrum.ieee.org/superaccurate-gps-chips-coming-to-smartphones-in-2018 |access-date=January 17, 2018 |work=IEEE Spectrum |date=September 21, 2017 |archive-url=https://web.archive.org/web/20180118011412/https://spectrum.ieee.org/tech-talk/semiconductors/design/superaccurate-gps-chips-coming-to-smartphones-in-2018 |archive-date=January 18, 2018 |url-status=live }}</ref> Consumer devices such as smartphones can be accurate to {{convert|4.9|m|abbr=on}} or better when used with assistive services like [[Wi-Fi positioning system|Wi-Fi positioning]].<ref>{{cite journal |url=https://www.nist.gov/how-do-you-measure-it/how-do-you-measure-your-location-using-gps|title=How Do You Measure Your Location Using GPS? |date=March 17, 2021 |access-date=March 7, 2022 |journal=NIST |publisher= National Institute of Standards and Technology}}</ref>

{{As of|2023|July}}, 18 GPS satellites broadcast L5 signals, which are considered pre-operational prior to being broadcast by a full complement of 24 satellites in 2027.<ref>{{cite web |title=New Civil Signals |url=https://www.gps.gov/systems/gps/modernization/civilsignals/ |website=GPS.gov |access-date=November 22, 2023}}</ref>