Editing Global Positioning System (section)

== History ==
[[File:AFSC Film, NAVSTAR GPS-Circa 1977.ogv|thumb|Air Force film introducing the Navstar Global Positioning System, circa 1977]]
[[File:GPS24goldenSMALL.gif|thumb|GPS constellation system animation]]

The GPS project was launched in the United States in 1973 to overcome the limitations of previous navigation systems,<ref>{{cite book|title=The global positioning system: a shared national asset: recommendations for technical improvements and enhancements|last1=National Research Council (U.S.). Committee on the Future of the Global Positioning System|last2=National Academy of Public Administration|publisher=National Academies Press|year=1995|isbn=978-0-309-05283-2|page=16|url=https://books.google.com/books?id=Za8RBP5iTYoC|access-date=August 16, 2013}}</ref> combining ideas from several predecessors, including classified engineering design studies from the 1960s. The [[U.S. Department of Defense]] developed the system, which originally used 24 satellites, for use by the United States military, and became fully operational in 1993. Civilian use was allowed from the 1980s. [[Roger L. Easton]] of the [[Naval Research Laboratory]], [[Ivan A. Getting]] of [[The Aerospace Corporation]], and [[Bradford Parkinson]] of the [[Applied Physics Laboratory]] are credited with inventing it.<ref name="DarrinO'Leary2009">{{cite book|author1=Ann Darrin|author2=Beth L. O'Leary|title=Handbook of Space Engineering, Archaeology, and Heritage|url=https://books.google.com/books?id=dTwIDun4MroC&q=Roger+Easton&pg=PA239|date=June 26, 2009|publisher=CRC Press|isbn=978-1-4200-8432-0|pages=239–240|access-date=July 28, 2021|archive-date=August 14, 2021|archive-url=https://web.archive.org/web/20210814192242/https://books.google.com/books?id=dTwIDun4MroC&q=Roger+Easton&pg=PA239|url-status=live}}</ref> The work of [[Gladys West]] on the creation of the mathematical geodetic Earth model is credited as instrumental in the development of computational techniques for detecting satellite positions with the precision needed for GPS.<ref>{{cite news |last=Butterly |first=Amelia |date=May 20, 2018 |title=100 Women: Gladys West – the 'hidden figure' of GPS |url=https://www.bbc.com/news/world-43812053 |url-status=live |archive-url=https://web.archive.org/web/20190213112200/https://www.bbc.com/news/world-43812053 |archive-date=February 13, 2019 |access-date=January 17, 2019 |work=BBC News}}</ref><ref>{{Cite news |last=Mohdin |first=Aamna |date=November 19, 2020 |title=Gladys West: the hidden figure who helped invent GPS |language=en-GB |work=The Guardian |url=https://www.theguardian.com/society/2020/nov/19/gladys-west-the-hidden-figure-who-helped-invent-gps |access-date=2023-11-29 |issn=0261-3077}}</ref>

The design of GPS is based partly on similar ground-based [[radio-navigation]] systems, such as [[LORAN]] and the [[Decca Navigator System]], developed in the early 1940s. In 1955, [[Friedwardt Winterberg]] proposed a test of [[general relativity]]—detecting time slowing in a strong gravitational field using accurate atomic clocks placed in orbit inside artificial satellites. Special and general relativity predicted that the clocks on GPS satellites, as observed by those on Earth, run 38 microseconds faster per day than those on the Earth. The design of GPS corrects for this difference; because without doing so, GPS calculated positions would accumulate errors of up to {{convert|10|km/day|sp=us|mi/day|0}}.<ref>{{cite book   |url=http://bourabai.kz/winter/satelliten.htm   |title=Relativistische Zeitdilatation eines künstlichen Satelliten (Relativistic time dilation of an artificial satellite   |publisher=Astronautica Acta II (in German) (25). Retrieved October 19, 2014   |access-date=October 20, 2014 |archive-url=https://web.archive.org/web/20140703080406/http://bourabai.kz/winter/satelliten.htm |archive-date=July 3, 2014 |url-status=live   }}</ref>

=== Predecessors ===

When the [[Soviet Union]] launched its first artificial satellite ([[Sputnik 1]]) in 1957, two American physicists, William Guier and George Weiffenbach, at [[Johns Hopkins University]]'s [[Applied Physics Laboratory]] (APL) monitored its radio transmissions.<ref name="guier-weiffenbach">{{cite journal|last1=Guier|first1=William H.|last2=Weiffenbach|first2=George C.|title=Genesis of Satellite Navigation |journal=Johns Hopkins APL Technical Digest|volume=19|issue=1|pages=178–181|year=1997|url=http://www.jhuapl.edu/techdigest/td/td1901/guier.pdf|access-date=April 9, 2012|archive-url=https://web.archive.org/web/20120512002742/http://www.jhuapl.edu/techdigest/td/td1901/guier.pdf|archive-date=May 12, 2012}}</ref> Within hours they realized that, because of the [[Doppler effect]], they could pinpoint where the satellite was along its orbit. The Director of the APL gave them access to their [[UNIVAC I]] computer to perform the heavy calculations required.

[[File:Managers for the Timation program.jpg|thumb|The [[Naval Research Laboratory]]’s managers for the Timation program and, later, the GPS program: [[Roger L. Easton]] (left) and [[Al Bartholemew]].]]

Early the next year, Frank McClure, the deputy director of the APL, asked Guier and Weiffenbach to investigate the inverse problem: pinpointing the user's location, given the satellite's. (At the time, the Navy was developing the submarine-launched [[UGM-27 Polaris|Polaris]] missile, which required them to know the submarine's location.) This led them and APL to develop the [[Transit (satellite)|TRANSIT]] system.<ref>{{citation |author=Johnson |first=Steven |title=Where good ideas come from, the natural history of innovation |year=2010 |place=New York |publisher=Riverhead Books}}</ref> In 1959, ARPA (renamed [[DARPA]] in 1972) also played a role in TRANSIT.<ref>{{cite book |last1=Worth |first1=Helen E. |url=http://space50.jhuapl.edu/pdfs/book.pdf |title=Transit to Tomorrow. Fifty Years of Space Research at The Johns Hopkins University Applied Physics Laboratory |last2=Warren |first2=Mame |year=2009 |access-date=March 3, 2013 |archive-url=https://web.archive.org/web/20201226045330/http://space50.jhuapl.edu/pdfs/book.pdf |archive-date=December 26, 2020 |url-status=live}}</ref><ref name="Alexandrow">{{cite web |author=Alexandrow |first=Catherine |date=April 2008 |title=The Story of GPS |url=http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2565 |archive-url=https://web.archive.org/web/20130224065525/http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2565 |archive-date=February 24, 2013}}</ref><ref name=gap>{{cite book
|url=http://www.darpa.mil/about/history/first_50_years.aspx|title=DARPA: 50 Years of Bridging the Gap|date=April 2008|archive-url=https://web.archive.org/web/20110506103713/http://www.darpa.mil/About/History/First_50_Years.aspx|archive-date=May 6, 2011}}</ref>

TRANSIT was first successfully tested in 1960.<ref>{{cite web|last=Howell|first=Elizabeth|title=Navstar: GPS Satellite Network|url=http://www.space.com/19794-navstar.html|publisher=SPACE.com|access-date=February 14, 2013|archive-url=https://web.archive.org/web/20130217140737/http://www.space.com/19794-navstar.html|archive-date=February 17, 2013|url-status=live}}</ref> It used a [[satellite constellation|constellation]] of five satellites and could provide a navigational fix approximately once per hour. In 1967, the U.S. Navy developed the [[Timation]] satellite, which proved the feasibility of placing accurate clocks in space, a technology required for GPS.<ref>{{Cite web |title=NRL Launched First Time-Based Navigation Satellite in 1967 |url=https://www.nrl.navy.mil/Media/News/Article/3411925/nrl-launched-first-time-based-navigation-satellite-in-1967/ |access-date=2025-01-05 |website=U.S. Naval Research Laboratory |language=en-US}}</ref>

In the 1970s, the ground-based [[Omega (navigation system)|OMEGA]] navigation system, based on phase comparison of signal transmission from pairs of stations,<ref>{{cite web |author=Proc |first=Jerry |title=Omega |url=http://www.jproc.ca/hyperbolic/omega.html |url-status=live |archive-url=https://web.archive.org/web/20100105155410/http://www.jproc.ca/hyperbolic/omega.html |archive-date=January 5, 2010 |access-date=December 8, 2009 |publisher=Jproc.ca}}</ref> became the first worldwide radio navigation system. Limitations of these systems drove the need for a more universal navigation solution with greater accuracy.

Although there were wide needs for accurate navigation in military and civilian sectors, almost none of those was seen as justification for the billions of dollars it would cost in research, development, deployment, and operation of a constellation of navigation satellites. During the [[Cold War]] [[arms race]], the nuclear threat to the existence of the United States was the one need that did justify this cost in the view of the United States Congress. This deterrent effect is why GPS was funded.{{citation needed|date=September 2024}} It is also the reason for the ultra-secrecy at that time. The [[nuclear triad]] consisted of the United States Navy's [[submarine-launched ballistic missile]]s (SLBMs) along with [[United States Air Force]] (USAF) [[strategic bomber]]s and [[intercontinental ballistic missile]]s (ICBMs). Considered vital to the [[nuclear strategy|nuclear deterrence]] posture, accurate determination of the SLBM launch position was a [[force multiplication|force multiplier]].

Precise navigation would enable United States [[ballistic missile submarine]]s to get an accurate fix of their positions before they launched their SLBMs.<ref>{{cite web |url=http://www.trimble.com/gps/whygps.shtml#0|archive-url=https://web.archive.org/web/20071018151253/http://www.trimble.com/gps/whygps.shtml#0|archive-date=October 18, 2007|title=Why Did the Department of Defense Develop GPS?|publisher=Trimble Navigation Ltd|access-date=January 13, 2010}}</ref> The USAF, with two-thirds of the nuclear triad, also had requirements for a more accurate and reliable navigation system. The U.S. Navy and U.S. Air Force were developing their own technologies in parallel to solve what was essentially the same problem. To increase the survivability of ICBMs, there was a proposal to use mobile launch platforms (comparable to the Soviet [[RT-23 Molodets|SS-24]] and [[RT-2PM Topol|SS-25]]) and so the need to fix the launch position had similarity to the SLBM situation.

In 1960, the Air Force proposed a radio-navigation system called MOSAIC (MObile System for Accurate ICBM Control) that was essentially a 3-D LORAN System. A follow-on study, Project 57, was performed in 1963 and it was "in this study that the GPS concept was born". That same year, the concept was pursued as Project 621B, which had "many of the attributes that you now see in GPS"<ref>{{cite web |url=http://www.aero.org/publications/crosslink/summer2002/01.html|title=Charting a Course Toward Global Navigation|publisher=The Aerospace Corporation|access-date=October 14, 2013|archive-url=https://web.archive.org/web/20021101215923/http://www.aero.org/publications/crosslink/summer2002/01.html|archive-date=November 1, 2002<!--, 01:01:18-->}}</ref> and promised increased accuracy for U.S. Air Force bombers as well as ICBMs.

[[File:Navigation Technology Satellite – II.jpg|thumb|Navigation Technology Satellite – II (Timation IV): NTS-II, the first satellite completely designed and built by NRL under GPS Joint Program funding. Launched June 23, 1977.]]

Updates from the Navy TRANSIT system were too slow for the high speeds of Air Force operation. The [[United States Naval Research Laboratory|Naval Research Laboratory]] (NRL) continued making advances with their [[Timation]] (Time Navigation) satellites, first launched in 1967, second launched in 1969, with the third in 1974 carrying the first [[atomic clock]] into orbit and the fourth launched in 1977.<ref>{{cite web|url=http://support.radioshack.com/support_tutorials/gps/gps_tmline.htm|title=A Guide to the Global Positioning System (GPS) – GPS Timeline|publisher=Radio Shack|access-date=January 14, 2010|archive-url=https://web.archive.org/web/20100213100725/http://support.radioshack.com/support_tutorials/gps/gps_tmline.htm|archive-date=February 13, 2010}}</ref>

Another important predecessor to GPS came from a different branch of the United States military. In 1964, the [[United States Army]] orbited its first Sequential Collation of Range ([[SECOR]]) satellite used for geodetic surveying.<ref>{{cite web|title=Geodetic Explorer – A Press Kit|date=October 29, 1965|access-date=October 20, 2015|publisher=NASA |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660002550_1966002550.pdf|archive-url=https://web.archive.org/web/20140211071631/http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660002550_1966002550.pdf|archive-date=February 11, 2014|url-status=live}}</ref> The SECOR system included three ground-based transmitters at known locations that would send signals to the satellite transponder in orbit. A fourth ground-based station, at an undetermined position, could then use those signals to fix its location precisely. The last SECOR satellite was launched in 1969.<ref>{{cite encyclopedia|url=http://www.astronautix.com/craft/secor.htm|title=SECOR Chronology|encyclopedia=Mark Wade's Encyclopedia Astronautica|access-date=January 19, 2010|archive-url=https://web.archive.org/web/20100116213013/http://astronautix.com/craft/secor.htm|archive-date=January 16, 2010}}</ref>

=== Development ===
With these parallel developments in the 1960s, it was realized that a superior system could be developed by synthesizing the best technologies from 621B, Transit, Timation, and SECOR in a multi-service program. Satellite orbital position errors, induced by variations in the [[gravity field]] and [[Refraction|radar refraction]] among others, had to be resolved. A team led by Harold L. Jury of Pan Am Aerospace Division in Florida from 1970 to 1973, used real-time data assimilation and recursive estimation to do so, reducing systematic and residual errors to a manageable level to permit accurate navigation.<ref>Jury, H. L., 1973, Application of Kalman Filter to Real-Time Navigation using Synchronous Satellites, Proceedings of the 10th International Symposium on Space Technology and Science, Tokyo, Japan, pp. 945–952.</ref>

During Labor Day weekend in 1973, a meeting of about twelve military officers at the Pentagon discussed the creation of a ''Defense Navigation Satellite System (DNSS)''. It was at this meeting that the real synthesis that became GPS was created. Later that year, the DNSS program was named ''Navstar.''<ref>{{cite web |url=http://www.au.af.mil/au/cadre/aspj/airchronicles/aureview/1981/may-jun/garwin.htm |title=MX Deployment Reconsidered |website=au.af.mil |archive-url=https://web.archive.org/web/20170625123356/http://www.airuniversity.af.mil/ |archive-date=June 25, 2017 |access-date=June 7, 2013}}</ref> Navstar is often erroneously considered an acronym for "NAVigation System using Timing And Ranging" but was never considered as such by the GPS Joint Program Office (TRW may have once advocated for a different navigational system that used that acronym).<ref>{{Cite book|url=https://history.nasa.gov/sp4801-chapter17.pdf|title=Societal Impact of Spaceflight|last1=Dick|first1=Steven|last2=Launius|first2=Roger|publisher=US Government Printing Office|year=2007|isbn=978-0-16-080190-7|location=Washington, DC|page=331|access-date=July 20, 2019|archive-url=https://web.archive.org/web/20130303214202/http://history.nasa.gov/sp4801-chapter17.pdf|archive-date=March 3, 2013|url-status=live}}</ref> With the individual satellites being associated with the name Navstar (as with the predecessors Transit and Timation), a more fully encompassing name was used to identify the constellation of Navstar satellites, ''Navstar-GPS''.<ref>{{cite book |author1=Rip |first=Michael Russell |url={{google books|plainurl=y|id=mB9W3H90KDUC}} |title=The Precision Revolution: GPS and the Future of Aerial Warfare |author2=James M. Hasik |publisher=Naval Institute Press |year=2002 |isbn=978-1-55750-973-4 |page=65 |access-date=January 14, 2010}}</ref> Ten "[[GPS Block I|Block I]]" prototype satellites were launched between 1978 and 1985 (an additional unit was destroyed in a launch failure).<ref name="ieee2008">{{cite journal | title = Evolution of the Global Navigation SatelliteSystem (GNSS) | first1 = Christopher J. | last1 = Hegarty | first2 = Eric | last2 = Chatre | journal = Proceedings of the IEEE | date = December 2008 | pages = 1902–1917 | doi = 10.1109/JPROC.2008.2006090 | volume=96| issue = 12 | s2cid = 838848 |issn = 0018-9219 }}</ref>

The effect of the ionosphere on radio transmission was investigated in a geophysics laboratory of [[Air Force Cambridge Research Laboratory]], renamed to Air Force Geophysical Research Lab (AFGRL) in 1974. AFGRL developed the Klobuchar model for computing [[ionosphere|ionospheric]] corrections to GPS location.<ref>{{cite web |title=ION Fellow – Mr. John A. Klobuchar |url=https://www.ion.org/awards/2003-ionfellow-Klobuchar.cfm |url-status=live |archive-url=https://web.archive.org/web/20171004140058/https://www.ion.org/awards/2003-ionfellow-Klobuchar.cfm |archive-date=October 4, 2017 |access-date=June 17, 2017 |website=www.ion.org}}</ref> Of note is work done by Australian space scientist [[Elizabeth Essex-Cohen]] at AFGRL in 1974. She was concerned with the curving of the paths of radio waves ([[atmospheric refraction]]) traversing the ionosphere from NavSTAR satellites.<ref>{{cite web |url=http://harveycohen.net/crcss |title=GPS Signal Science |website=harveycohen.net |archive-url=https://web.archive.org/web/20170529200107/http://harveycohen.net/crcss/ |archive-date=May 29, 2017}}</ref>

After [[Korean Air Lines Flight 007]], a [[Boeing 747]] carrying 269 people, was shot down by a Soviet [[interceptor aircraft]] after straying in [[prohibited airspace]] because of navigational errors,<ref>{{cite web|url=http://www.icao.int/cgi/goto_m.pl?icao/en/trivia/kal_flight_007.htm |title=ICAO Completes Fact-Finding Investigation |publisher=International Civil Aviation Organization |access-date=September 15, 2008 |archive-url=https://web.archive.org/web/20080517005421/http://www.icao.int/cgi/goto_m.pl?icao%2Fen%2Ftrivia%2Fkal_flight_007.htm |archive-date=May 17, 2008 }}</ref> in the vicinity of [[Sakhalin]] and [[Moneron Island]]s, President [[Ronald Reagan]] issued a directive making GPS freely available for civilian use, once it was sufficiently developed, as a common good.<ref name="KAL007">{{cite news|url=http://iipdigital.usembassy.gov/st/english/article/2006/02/20060203125928lcnirellep0.5061609.html|archive-url=https://web.archive.org/web/20131009161500/http://iipdigital.usembassy.gov/st/english/article/2006/02/20060203125928lcnirellep0.5061609.html|archive-date=October 9, 2013|access-date=June 17, 2019|title=United States Updates Global Positioning System Technology|publisher=America.gov|date=February 3, 2006}}</ref> The first Block II satellite was launched on February 14, 1989,<ref>{{cite book|last1=Rumerman|first1=Judy A.|title=NASA Historical Data Book, Volume VII|date=2009|publisher=NASA|page=136|url=https://history.nasa.gov/SP-4012v7ch2.pdf|access-date=July 12, 2017|archive-url=https://web.archive.org/web/20171225230629/https://history.nasa.gov/SP-4012v7ch2.pdf|archive-date=December 25, 2017|url-status=live}}</ref> and the 24th&nbsp;satellite was launched in 1994. The GPS program cost at this point, not including the cost of the user equipment but including the costs of the satellite launches, has been estimated at US$5&nbsp;billion (equivalent to ${{Inflation|US|5|1994|fmt=c}} billion in {{Inflation/year|US}}).<ref>Scott Pace, Gerald P. Frost, Irving Lachow, David R. Frelinger, Donna Fossum, Don Wassem, Monica M. Pinto. The Global Positioning System Assessing National Policies, Rand Corporation, 1995, [https://www.rand.org/content/dam/rand/pubs/monograph_reports/MR614/MR614.appb.pdf Appendix B]. {{Webarchive|url=https://web.archive.org/web/20160304094441/https://www.rand.org/content/dam/rand/pubs/monograph_reports/MR614/MR614.appb.pdf|date=March 4, 2016}}, GPS History, Chronology, and Budgets.</ref>

Initially, the highest-quality signal was reserved for military use, and the signal available for civilian use was intentionally degraded, in a policy known as [[Selective Availability]]. This changed on May 1, 2000, with U.S. President [[Bill Clinton]] signing a policy directive to turn off Selective Availability to provide the same accuracy to civilians that was afforded to the military. The directive was proposed by the U.S. Secretary of Defense, [[William J. Perry|William Perry]], in view of the widespread growth of [[differential GPS]] services by private industry to improve civilian accuracy. Moreover, the U.S. military was developing technologies to deny GPS service to potential adversaries on a regional basis.<ref>{{cite web|url=http://ngs.woc.noaa.gov/FGCS/info/sans_SA/docs/GPS_SA_Event_QAs.pdf |title=GPS & Selective Availability Q&A |publisher=NOAA |access-date=May 28, 2010 |archive-url=https://web.archive.org/web/20050921115614/http://ngs.woc.noaa.gov/FGCS/info/sans_SA/docs/GPS_SA_Event_QAs.pdf |archive-date=September 21, 2005 }}</ref> Selective Availability was removed from the GPS architecture beginning with GPS-III.

Since its deployment, the U.S. has implemented several improvements to the GPS service, including new signals for civil use and increased accuracy and integrity for all users, all the while maintaining compatibility with existing GPS equipment. Modernization of the satellite system has been an ongoing initiative by the U.S. Department of Defense through a series of [[GPS Block IIIA|satellite acquisitions]] to meet the growing needs of the military, civilians, and the commercial market. As of early 2015, high-quality Standard Positioning Service (SPS) GPS receivers provided horizontal accuracy of better than {{convert|3.5|m|sp=us||}},<ref name="gpsgovaccurary" /> although many factors such as receiver and antenna quality and atmospheric issues can affect this accuracy.

GPS is owned and operated by the United States government as a national resource. The Department of Defense is the steward of GPS. The ''Interagency GPS Executive Board (IGEB)'' oversaw GPS policy matters from 1996 to 2004. After that, the National Space-Based Positioning, Navigation and Timing Executive Committee was established by presidential directive in 2004 to advise and coordinate federal departments and agencies on matters concerning the GPS and related systems.<ref>{{cite web|last=Steitz|first=David E.|title=National Positioning, Navigation and Timing Advisory Board Named|url=http://www.nasa.gov/home/hqnews/2007/mar/HQ_07071_National_PNT_Advisory_Board.txt|access-date=March 22, 2007|archive-url=https://web.archive.org/web/20100113234255/http://www.nasa.gov/home/hqnews/2007/mar/HQ_07071_National_PNT_Advisory_Board.txt|archive-date=January 13, 2010|url-status=live}}</ref> The executive committee is chaired jointly by the Deputy Secretaries of Defense and Transportation. Its membership includes equivalent-level officials from the Departments of State, Commerce, and Homeland Security, the [[Joint Chiefs of Staff]] and [[NASA]]. Components of the executive office of the president participate as observers to the executive committee, and the FCC chairman participates as a liaison.

The U.S. Department of Defense is required by law to "maintain a Standard Positioning Service (as defined in the federal radio navigation plan and the standard positioning service signal specification) that will be available on a continuous, worldwide basis" and "develop measures to prevent hostile use of GPS and its augmentations without unduly disrupting or degrading civilian uses".

=== Timeline and modernization ===
{{prose|section|date=July 2023}}
[[File:GPS-0012 San Diego Air & Space Museum.jpg|thumb|[[Test article (aerospace)|Qualification vehicle]] for GPS Block II on display in [[San Diego Air & Space Museum|San Diego]] – the only vehicle on public display.<ref>{{Cite web |last=Czopek |first=Frank |title=GPS 12 |url=https://www.ion.org/museum/item_view.cfm?cid=4&scid=15&iid=23 |access-date=October 14, 2024 |website=Institute of Navigation – Navigation Museum}}</ref>]]
{|class="wikitable"
|+ Summary of satellites<ref>[http://www.insidegnss.com/node/918 GPS Wing Reaches GPS III IBR Milestone] {{Webarchive|url=https://web.archive.org/web/20130523204537/http://www.insidegnss.com/node/918 |date=May 23, 2013 }} in ''[[Inside GNSS]]'' November 10, 2008</ref><ref>{{cite web |url=http://www.navcen.uscg.gov/?Do=constellationStatus |title=GPS Constellation Status for 08/26/2015 |access-date=August 26, 2015 |archive-url=https://web.archive.org/web/20150905082039/http://www.navcen.uscg.gov/?Do=constellationStatus |archive-date=September 5, 2015 |url-status=live }}</ref><ref>{{cite web|url=http://spaceflightnow.com/2015/10/31/recap-story-three-atlas-5-launch-successes-in-one-month/|title=Recap story: Three Atlas 5 launch successes in one month|date=October 31, 2015 |access-date=October 31, 2015|archive-url=https://web.archive.org/web/20151101182626/http://spaceflightnow.com/2015/10/31/recap-story-three-atlas-5-launch-successes-in-one-month/|archive-date=November 1, 2015|url-status=live}}</ref>
! rowspan="2" | Block || rowspan="2" | Launch <br />period || colspan="4" | Satellite launches || rowspan="2" | Currently<br /> in orbit<br /> and healthy
|-
! Success || Failure || In<br>preparation || Planned
|-
! [[GPS Block I|I]]
| 1978–1985 || 10 || 1 || 0 ||  0 || 0
|-
! [[GPS Block II|II]]
| 1989–1990 || 9 || 0 || 0 || 0 || 0
|-
! [[GPS Block IIA|IIA]]
| 1990–1997 || 19 || 0 || 0 || 0 || 0
|-
! [[GPS Block IIR|IIR]]
| 1997–2004 ||12|| 1 || 0 || 0 || 7
|-
! [[GPS Block IIR-M|IIR-M]]
| 2005–2009 || 8 || 0 || 0 || 0 || 7
|-
! [[GPS Block IIF|IIF]]
| 2010–2016  || 12 || 0 || 0 || 0 || 11
|-
! [[GPS Block IIIA|IIIA]]
| 2018–  || 6 || 0 || 4 || 0 || 6
|-
! [[GPS Block IIIF|IIIF]]
| —          || 0 || 0 || 0 || 22 || 0
|-
! colspan="2" | Total
| 76 || 2 || 4 || 22 || 31
|-
| colspan="7" style="font-size: smaller;" | (Last update: September 26, 2024)<br />
[[USA-203]] from Block IIR-M is unhealthy<br /><ref>{{cite web|url=http://www.navcen.uscg.gov/?pageName=gpsAlmanacs|title=GPS almanacs|publisher=Navcen.uscg.gov|access-date=October 15, 2010|archive-url=https://web.archive.org/web/20100923053920/http://www.navcen.uscg.gov/?pageName=gpsAlmanacs|archive-date=September 23, 2010|url-status=live}}</ref> For a more complete list, see ''[[List of GPS satellites]]''
|}
* In 1972, the U.S. Air Force Central Inertial Guidance Test Facility (Holloman Air Force Base) conducted developmental flight tests of four prototype GPS receivers in a Y configuration over [[White Sands Missile Range]], using ground-based pseudo-satellites.<ref>{{cite web|url=https://www.rewiresecurity.co.uk/blog/gps-global-positioning-system-satellites|title=Origin of Global Positioning System (GPS)|website=Rewire Security|access-date=February 9, 2017|archive-url=https://web.archive.org/web/20170211080457/https://www.rewiresecurity.co.uk/blog/gps-global-positioning-system-satellites|archive-date=February 11, 2017|url-status=live}}</ref>
* In 1978, the first experimental Block-I GPS satellite was launched.<ref name="ieee2008" />
* In 1983, after Soviet Union interceptor aircraft shot down the civilian airliner [[Korean Air Flight 007|KAL 007]] that strayed into [[prohibited airspace]] because of navigational errors, killing all 269&nbsp;people on board, U.S. President [[Ronald Reagan]] announced that GPS would be made available for civilian uses once it was completed,<ref name=":2" /><ref>{{cite book |last1=Schroeer |first1=Dietrich |url={{google books|plainurl=y|id=I7JRAAAAMAAJ}} |title=Technology Transfer |last2=Elena |first2=Mirco |publisher=Ashgate |year=2000 |isbn=978-0-7546-2045-7 |page=80 |access-date=May 25, 2008}}</ref><ref>{{cite book|url={{google books|plainurl=y|id=_wpUAAAAMAAJ}}|title=The Precision Revolution: GPS and the Future of Aerial Warfare|author1=Michael Russell Rip |author2=James M. Hasik |publisher=Naval Institute Press|year=2002|isbn=978-1-55750-973-4|access-date=May 25, 2008}}</ref> although it had been publicly known as early as 1979, that the CA code (Coarse/Acquisition code) would be available to civilian users.<ref name="breeze-19790916-91">{{cite news |last1=Dore |first1=Richard |date=September 16, 1979 |title=Navstar – Global system will provide accurate data for navigation |url=https://www.newspapers.com/article/the-daily-breeze-navstar-global-system/125171841/ |url-status=live |archive-url=https://web.archive.org/web/20230523113102/https://www.newspapers.com/article/the-daily-breeze-navstar-global-system/125171841/ |archive-date=May 23, 2023 |access-date=May 23, 2023 |newspaper=[[The Daily Breeze]] |location=[[Torrance, California]] |page=91 |via=Newspapers.com}}</ref><ref name="breeze-19790916-97">{{cite news |last1=Dore |first1=Richard |title=Satellite technology key to GPS |url=https://www.newspapers.com/article/the-daily-breeze-satellite-technology-ke/125171984/ |access-date=May 23, 2023 |newspaper=[[The Daily Breeze]] |date=September 16, 1979 |archive-url=https://web.archive.org/web/20230523113718/https://www.newspapers.com/article/the-daily-breeze-satellite-technology-ke/125171984/ |archive-date=May 23, 2023 |url-status=live |page=97 |location=[[Torrance, California]] |via=Newspapers.com }}</ref>
* By 1985, ten more experimental Block-I satellites had been launched to validate the concept.
* Beginning in 1988, command and control of these satellites was moved from [[Onizuka AFS]], California to the [[2nd Space Operations Squadron|2nd Satellite Control Squadron]] (2SCS) located at [[Schriever Space Force Base]] in [[Colorado Springs, Colorado]].<ref>{{cite web|title=AF Space Command Chronology |url=http://www.afspc.af.mil/heritage/chronology.asp |publisher=USAF Space Command |access-date=June 20, 2011 |archive-url=https://web.archive.org/web/20110817001221/http://www.afspc.af.mil/heritage/chronology.asp |archive-date=August 17, 2011 }}</ref><ref>{{cite web|title=FactSheet: 2nd Space Operations Squadron |url=http://www.schriever.af.mil/library/factsheets/factsheet.asp?id=4045 |publisher=USAF Space Command |access-date=June 20, 2011 |archive-url=https://web.archive.org/web/20110611205433/http://www.schriever.af.mil/library/factsheets/factsheet.asp?id=4045 |archive-date=June 11, 2011 }}</ref>
* On February 14, 1989, the first modern Block-II satellite was launched.
* The [[Gulf War]] from 1990 to 1991 was the first conflict in which the military widely used GPS.<ref>[https://www.rand.org/pubs/monograph_reports/MR614.html The Global Positioning System: Assessing National Policies] {{Webarchive|url=https://web.archive.org/web/20151230101234/http://www.rand.org/pubs/monograph_reports/MR614.html |date=December 30, 2015 }}, p.245. RAND corporation</ref>
* In 1991, DARPA's project to create a miniature GPS receiver successfully ended, replacing the previous {{cvt|16|kg|||}} military receivers with a {{cvt|1.25|kg|||}} all-digital handheld GPS receiver.<ref name=Alexandrow />
* In 1991, [[TomTom]], a Dutch sat-nav manufacturer was founded.
* In 1992, the [[2nd Space Wing]], which originally managed the system, was inactivated and replaced by the [[50th Space Wing]].
* By December 1993, GPS achieved [[initial operational capability]] (IOC), with a full constellation (24 satellites) available and providing the Standard Positioning Service (SPS).<ref name="IOCFOC">{{cite web|url=http://tycho.usno.navy.mil/gpsinfo.html|title=USNO NAVSTAR Global Positioning System|publisher=U.S. Naval Observatory|access-date=January 7, 2011|archive-url=https://web.archive.org/web/20110126200746/http://tycho.usno.navy.mil/gpsinfo.html|archive-date=January 26, 2011}}</ref>
* Full Operational Capability (FOC) was declared by [[Air Force Space Command]] (AFSPC) in April 1995, signifying full availability of the military's secure Precise Positioning Service (PPS).<ref name="IOCFOC" />
* In 1996, recognizing the importance of GPS to civilian users as well as military users, U.S. President [[Bill Clinton]] issued a policy directive<ref>[[National Archives and Records Administration]]. [http://clinton4.nara.gov/textonly/WH/EOP/OSTP/html/gps-factsheet.html U.S. Global Positioning System Policy] {{Webarchive|url=https://web.archive.org/web/20060406125528/http://clinton4.nara.gov/textonly/WH/EOP/OSTP/html/gps-factsheet.html |date=April 6, 2006 }}. March 29, 1996.</ref> declaring GPS a [[dual-use]] system and establishing an [[Interagency GPS Executive Board]] to manage it as a national asset.
* In 1998, United States Vice President [[Al Gore]] announced plans to upgrade GPS with two new civilian signals for enhanced user accuracy and reliability, particularly with respect to aviation safety, and in 2000 the [[United States Congress]] authorized the effort, referring to it as ''[[GPS III]]''.
* On May 2, 2000 "Selective Availability" was discontinued as a result of the 1996 executive order, allowing civilian users to receive a non-degraded signal globally.
* In 2004, the United States government signed an agreement with the European Community establishing cooperation related to GPS and Europe's [[Galileo (satellite navigation)|Galileo system]].
* In 2004, United States President [[George W. Bush]] updated the national policy and replaced the executive board with the National Executive Committee for Space-Based Positioning, Navigation, and Timing.<ref>{{cite web|url=http://pnt.gov/ |title=National Executive Committee for Space-Based Positioning, Navigation, and Timing |publisher=Pnt.gov |access-date=October 15, 2010 |archive-url=https://web.archive.org/web/20100528124826/http://pnt.gov/ |archive-date=May 28, 2010 }}</ref><!-- [[National Space-Based Positioning, Navigation, and Timing Executive Committee]] -->
* In November 2004, [[Qualcomm]] announced successful tests of [[assisted GPS]] for [[mobile phones]].<ref>{{cite web|url=http://www.3g.co.uk/PR/November2004/8641.htm|title=Assisted-GPS Test Calls for 3G WCDMA Networks|date=November 10, 2004|publisher=3g.co.uk|access-date=November 24, 2010|archive-url=https://web.archive.org/web/20101127041459/http://www.3g.co.uk/PR/November2004/8641.htm|archive-date=November 27, 2010}}</ref>
* In 2005, the first modernized GPS satellite was launched and began transmitting a second civilian signal (L2C) for enhanced user performance.<ref>{{cite web|title=Press release: First Modernized GPS Satellite Built by Lockheed Martin Launched Successfully by the U.S. Air Force – Sep 26, 2005|url=http://news.lockheedmartin.com/2005-09-26-First-Modernized-GPS-Satellite-Built-by-Lockheed-Martin-Launched-Successfully-by-the-U-S-Air-Force|publisher=Lockheed Martin|ref=September 26, 2005|language=en|access-date=August 9, 2017|archive-url=https://web.archive.org/web/20170810090450/http://news.lockheedmartin.com/2005-09-26-First-Modernized-GPS-Satellite-Built-by-Lockheed-Martin-Launched-Successfully-by-the-U-S-Air-Force|archive-date=August 10, 2017|url-status=live}}</ref>
* On September 14, 2007, the aging mainframe-based [[Ground segment]] Control System was transferred to the new Architecture Evolution Plan.<ref>{{cite web|url=https://www.losangeles.spaceforce.mil/?id=123068412 |title=losangeles.af.mil |publisher=losangeles.af.mil |date=September 17, 2007 |access-date=October 15, 2010 |url-status=live |archive-url=https://web.archive.org/web/20110511192610/http://www.losangeles.af.mil/news/story.asp?id=123068412 |archive-date=May 11, 2011 }}</ref>
* On May 19, 2009, the United States [[Government Accountability Office]] issued a report warning that some GPS satellites could fail as soon as 2010.<ref>{{cite news|url=https://www.theguardian.com/technology/2009/may/19/gps-close-to-breakdown|title=GPS system 'close to breakdown'|last=Johnson|first=Bobbie|newspaper=The Guardian|date=May 19, 2009|access-date=December 8, 2009|location=London|archive-url=https://web.archive.org/web/20130926155833/http://www.theguardian.com/technology/2009/may/19/gps-close-to-breakdown|archive-date=September 26, 2013|url-status=live}}</ref>
* On May 21, 2009, the [[Air Force Space Command]] allayed fears of GPS failure, saying: "There's only a small risk we will not continue to exceed our performance standard."<ref>{{cite news|url=https://abcnews.go.com/Technology/AheadoftheCurve/story?id=7647002&page=1|title=Air Force Responds to GPS Outage Concerns|last=Coursey|first=David|date=May 21, 2009|work=ABC News|access-date=May 22, 2009|archive-url=https://web.archive.org/web/20090523175214/http://abcnews.go.com/Technology/AheadoftheCurve/story?id=7647002&page=1|archive-date=May 23, 2009|url-status=live}}</ref>
* On January 11, 2010, an update of ground control systems caused a software incompatibility with 8,000 to 10,000 military receivers manufactured by a division of Trimble Navigation Limited of Sunnyvale, California.{{clarify|date=March 2022|reason=What was the outcome?}}<ref>{{cite news|url=https://www.huffingtonpost.com/2010/06/01/air-force-gps-problem-gli_n_595727.html|title=Air Force GPS Problem: Glitch Shows How Much U.S. Military Relies On GPS|work=The Huffington Post|date=June 1, 2010 |first1=Dan |last1=Elliott |access-date=October 15, 2010|archive-url=https://web.archive.org/web/20110511200835/https://www.huffingtonpost.com/2010/06/01/air-force-gps-problem-gli_n_595727.html |archive-date=May 11, 2011 }}</ref>
* On February 25, 2010,<ref>{{cite web|url=https://www.losangeles.spaceforce.mil/?id=123192234 |title=Contract Award for Next Generation GPS Control Segment Announced |website=Los Angeles Air Force Base |date= February 25, 2010 |access-date=December 14, 2012 |url-status=live |archive-url=https://web.archive.org/web/20130723134812/http://www.losangeles.af.mil/news/story_print.asp?id=123192234 |archive-date=July 23, 2013 }}</ref> the U.S. Air Force awarded the contract to [[Raytheon Company]] to develop the GPS Next Generation Operational Control System (OCX) to improve accuracy and availability of GPS navigation signals, and serve as a critical part of GPS modernization.
* July 24, 2020, operation of the GPS constellation is transferred to the newly established [[United States Space Force|U.S. Space Force]] as part of its establishment.<ref name="2nd Space Operations Squadron">{{Cite web |title=2nd Space Operations Squadron |url=https://www.petersonschriever.spaceforce.mil/About-Us/Fact-Sheets/Display/Article/2814232/2nd-space-operations-squadron/ |access-date=2024-10-15 |website=Peterson and Schriever Space Force Base |language=en-US}}</ref> [[File:2nd Space Operations Squadron emblem.png|thumb|266x266px|Emblem of the [[2nd Space Operations Squadron]] – the unit responsible for operating the constellation ]]
* On October 13, 2023, the Space Force activated [[Positioning, Navigation, and Timing Integrated Mission Delta (Provisional)|PNT Delta (Provisional)]] to manage US [[Satellite navigation|navigation warfare]] assets. [[2nd Space Operations Squadron|2SOPS]] and GPS operations were realigned under this new [[Structure of the United States Space Force|Delta]].<ref name="2nd Space Operations Squadron"/>

=== Awards ===
[[File:Dr Gladys West.jpg|alt=Air Force Space Commander presents Gladys West with an award as she is inducted into the Air Force Space and Missile Pioneers Hall of Fame for her GPS work on December 6, 2018.|thumb|AFSPC Vice Commander Lt. Gen. D. T. Thompson presents Gladys West with an award as she is inducted into the Air Force Space and Missile Pioneers Hall of Fame.]]
On February 10, 1993, the [[National Aeronautic Association]] selected the GPS Team as winners of the 1992 [[Collier Trophy|Robert J. Collier Trophy]], the US's most prestigious aviation award. This team combines researchers from the Naval Research Laboratory, the U.S. Air Force, the [[Aerospace Corporation]], [[Rockwell International]] Corporation, and [[IBM]] Federal Systems Company. The citation honors them "for the most significant development for safe and efficient navigation and surveillance of air and spacecraft since the introduction of radio navigation 50&nbsp;years ago".

Two GPS developers received the [[United States National Academy of Engineering|National Academy of Engineering]] [[Charles Stark Draper Prize]] for 2003:
* [[Ivan Getting]], emeritus president of [[The Aerospace Corporation]] and an engineer at [[Massachusetts Institute of Technology]], established the basis for GPS, improving on the [[World War II]] land-based radio system called LORAN (''Lo''ng-range ''R''adio ''A''id to ''N''avigation).
* [[Bradford Parkinson]], professor of [[aeronautics]] and [[astronautics]] at [[Stanford University]], conceived the present satellite-based system in the early 1960s and developed it in conjunction with the U.S. Air Force. Parkinson served twenty-one years in the Air Force, from 1957 to 1978, and retired with the rank of colonel.

GPS developer [[Roger L. Easton]] received the [[National Medal of Technology]] on February 13, 2006.<ref>{{cite web |url-status=live |agency=[[United States Naval Research Laboratory]] |url=http://www.eurekalert.org/pub_releases/2005-11/nrl-par112205.php |title=President announces Roger Easton recipient of National Medal of Technology |archive-url=https://web.archive.org/web/20071011075824/http://eurekalert.org/pub_releases/2005-11/nrl-par112205.php |archive-date=October 11, 2007 |date=November 22, 2005 |website=EurekAlert! }}</ref> [[Francis X. Kane]] (Col. USAF, ret.) was inducted into the U.S. Air Force Space and Missile Pioneers Hall of Fame at Lackland A.F.B., San Antonio, Texas, March 2, 2010, for his role in space technology development and the engineering design concept of GPS conducted as part of Project 621B. In 1998, GPS technology was inducted into the [[Space Foundation]] [[Space Technology Hall of Fame]].<ref>{{cite web|title= Inducted Technologies / 1998: Global Positioning System (GPS) |website=Space Technology Hall of Fame |url=http://www.spacetechhalloffame.org/inductees_1998_Global_Positioning_System.html |archive-url=https://web.archive.org/web/20120612064112/http://www.spacetechhalloffame.org/inductees_1998_Global_Positioning_System.html |archive-date=June 12, 2012 }}</ref>

On October 4, 2011, the [[International Astronautical Federation]] (IAF) awarded the Global Positioning System (GPS) its 60th Anniversary Award, nominated by IAF member, the American Institute for Aeronautics and Astronautics (AIAA). The IAF Honors and Awards Committee recognized the uniqueness of the GPS program and the exemplary role it has played in building international collaboration for the benefit of humanity.<ref>{{cite web|url=https://www.gps.gov/news/2011/10/IAC-award/|title=GPS Program Receives International Award|date=October 5, 2011|website=GPS.gov |first1=Richard A. |last1=Williams Jr. |archive-url=https://web.archive.org/web/20170513140254/http://www.gps.gov/news/2011/10/IAC-award/|archive-date=May 13, 2017|access-date=December 24, 2018}}</ref> On December 6, 2018, Gladys West was inducted into the Air Force Space and Missile Pioneers Hall of Fame in recognition of her work on an extremely accurate geodetic Earth model, which was ultimately used to determine the orbit of the GPS constellation.<ref>{{Cite web|title=Mathematician inducted into Space and Missiles Pioneers Hall of Fame|url=https://www.afspc.af.mil/News/Article-Display/Article/1707464/mathematician-inducted-into-space-and-missiles-pioneers-hall-of-fame/|access-date=August 3, 2021|website=Air Force Space Command |date=December 7, 2018 |language=en-US|archive-date=June 3, 2019|archive-url=https://web.archive.org/web/20190603171222/https://www.afspc.af.mil/News/Article-Display/Article/1707464/mathematician-inducted-into-space-and-missiles-pioneers-hall-of-fame/|url-status=dead}}</ref><ref>{{Cite web |title=dinh vi gps |url=https://dinhvigps.vn/ |access-date=2025-01-05 |website= |language=en}}</ref> On February 12, 2019, four founding members of the project were awarded the Queen Elizabeth Prize for Engineering with the chair of the awarding board stating: "Engineering is the foundation of civilisation; ...They've re-written, in a major way, the infrastructure of our world."<ref>{{cite news|url=https://www.bbc.com/news/science-environment-47212151|title=Queen Elizabeth Prize for Engineering: GPS pioneers lauded |first=Jonathan|last=Amos|work=BBC News|date=February 12, 2019|access-date=April 6, 2019|archive-url=https://web.archive.org/web/20190406234539/https://www.bbc.com/news/science-environment-47212151|archive-date=April 6, 2019|url-status=live}}</ref>