Editing Global Positioning System (section)

=== Control segment ===
[[File:GPS monitor station.jpg|right|thumb|upright=0.8|Ground monitor station used from 1984 to 2007, on display at the [[Air Force Space and Missile Museum]]]]

The control segment (CS) is composed of:
# a master control station (MCS),
# an alternative master control station,
# four dedicated ground antennas, and
# six dedicated monitor stations.

The MCS can also access [[Satellite Control Network]] (SCN) ground antennas (for additional command and control capability) and NGA ([[National Geospatial-Intelligence Agency]]) monitor stations. The flight paths of the satellites are tracked by dedicated U.S. Space Force monitoring stations in Hawaii, [[Kwajalein Atoll]], [[Ascension Island]], [[Diego Garcia]], [[Colorado Springs, Colorado]] and [[Cape Canaveral]], Florida, along with shared NGA monitor stations operated in England, Argentina, Ecuador, Bahrain, Australia and Washington, DC.<ref>United States Coast Guard. [https://archive.today/20120712041201/http://igs.bkg.bund.de/root_ftp/IGS/mail/igsmail/year2005/5209 General GPS News 9–9–05].</ref> The tracking information is sent to the MCS at [[Schriever Space Force Base]] {{convert|25|km|mi|abbr=on}} ESE of Colorado Springs, which is operated by the [[2nd Space Operations Squadron]] (2&nbsp;SOPS) of the U.S. Space Force. Then 2&nbsp;SOPS contacts each GPS satellite regularly with a navigational update using dedicated or shared (AFSCN) ground antennas (GPS dedicated ground antennas are located at [[Kwajalein]], [[Ascension Island]], [[Diego Garcia]], and [[Cape Canaveral]]). These updates synchronize the atomic clocks on board the satellites to within a few [[nanosecond]]s of each other, and adjust the [[ephemeris]] of each satellite's internal orbital model. The updates are created by a [[Kalman filter]] that uses inputs from the ground monitoring stations, [[space weather]] information, and various other inputs.<ref>[[USNO]] [http://tycho.usno.navy.mil/gpsinfo.html NAVSTAR Global Positioning System] {{Webarchive|url=https://web.archive.org/web/20060208110241/http://tycho.usno.navy.mil/gpsinfo.html |date=February 8, 2006 }}. Retrieved May 14, 2006.</ref>

When a satellite's orbit is being adjusted, the satellite is marked ''unhealthy'', so receivers do not use it. After the maneuver, engineers track the new orbit from the ground, upload the new ephemeris, and mark the satellite healthy again. The operation control segment (OCS) currently serves as the control segment of record. It provides the operational capability that supports GPS users and keeps the GPS operational and performing within specification.

OCS replaced the 1970s-era mainframe computer at Schriever Air Force Base in September 2007. After installation, the system helped enable upgrades and provide a foundation for a new security architecture that supported U.S. armed forces.

{{anchor|OCX}}OCS will continue to be the ground control system of record until the new segment, Next Generation GPS Operation Control System<ref name="losangelesmil" /> (OCX), is fully developed and functional. The U.S. Department of Defense has claimed that the new capabilities provided by OCX will be the cornerstone for enhancing GPS's mission capabilities, enabling U.S. Space Force to enhance GPS operational services to U.S. combat forces, civil partners and domestic and international users.<ref>{{Cite web |title=DoD Decision Breathes New Life into Critical OCX Satellite Program |url=https://www.defense.gov/News/News-Stories/Article/Article/974228/dod-decision-breathes-new-life-into-critical-ocx-satellite-program/https://www.defense.gov/News/News-Stories/Article/Article/974228/dod-decision-breathes-new-life-into-critical-ocx-satellite-program/ |access-date=2023-11-26 |website=U.S. Department of Defense |language=en-US}}{{dead link|date=April 2025|bot=medic}}{{cbignore|bot=medic}}</ref><ref>{{Cite web |title=GPS.gov: Next Generation Operational Control System (OCX) |url=https://www.gps.gov/systems/gps/control/OCX/ |access-date=2023-11-26 |website=www.gps.gov}}</ref> The GPS OCX program also will reduce cost, schedule and technical risk. It is designed to provide 50%<ref>{{cite web|url=http://www.defenseindustrydaily.com/The-USAs-GPS-III-Satellites-04900/|title=The USA's GPS-III Satellites|date=October 13, 2011|publisher=Defense Industry Daily|access-date=October 27, 2011|archive-url=https://web.archive.org/web/20111018184806/http://www.defenseindustrydaily.com/The-USAs-GPS-III-Satellites-04900/|archive-date=October 18, 2011|url-status=live}}</ref> sustainment cost savings through efficient software architecture and Performance-Based Logistics. In addition, GPS OCX is expected to cost millions of dollars less than the cost to upgrade OCS while providing four times the capability.

The GPS OCX program represents a critical part of GPS modernization and provides information assurance improvements over the current GPS OCS program.
* OCX will have the ability to control and manage GPS legacy satellites as well as the next generation of GPS III satellites, while enabling the full array of military signals.
* Built on a flexible architecture that can rapidly adapt to changing needs of GPS users allowing immediate access to GPS data and constellation status through secure, accurate and reliable information.
* Provides the warfighter with more secure, actionable and predictive information to enhance situational awareness.
* Enables new modernized signals (L1C, L2C, and L5) and has M-code capability, which the legacy system is unable to do.
* Provides significant information assurance improvements over the current program including detecting and preventing cyber attacks, while isolating, containing and operating during such attacks.
* Supports higher volume near real-time command and control capabilities and abilities.

On September 14, 2011,<ref>{{cite web|url=http://www.comspacewatch.com/news/viewpr.html?pid=34625|title=GPS Completes Next Generation Operational Control System PDR|date=September 14, 2011|publisher=Air Force Space Command News Service|archive-url=https://web.archive.org/web/20111002043642/http://www.comspacewatch.com/news/viewpr.html?pid=34625|archive-date=October 2, 2011}}</ref> the U.S. Air Force announced the completion of GPS OCX Preliminary Design Review and confirmed that the OCX program is ready for the next phase of development. The GPS OCX program missed major milestones and pushed its launch into 2021, 5 years past the original deadline. According to the Government Accounting Office in 2019, the 2021 deadline looked shaky.<ref>{{cite web|url=https://www.gao.gov/assets/700/699234.pdf|title=GLOBAL POSITIONING SYSTEM: Updated Schedule Assessment Could Help Decision Makers Address Likely Delays Related to New Ground Control System|date=May 2019|publisher=US Government Accounting Office|access-date=August 24, 2019|archive-date=September 10, 2019|archive-url=https://web.archive.org/web/20190910233141/https://www.gao.gov/assets/700/699234.pdf|url-status=live}}</ref>

The project remained delayed in 2023, and was (as of June 2023) 73% over its original estimated budget.<ref>{{Cite news |date=June 21, 2023 |title=Raytheon's $7 Billion GPS Stations Are Running 73% Over Estimates |language=en |work=Bloomberg.com |url=https://www.bloomberg.com/news/articles/2023-06-21/raytheon-s-7-billion-ocx-gps-ground-stations-draw-the-ire-of-house-panel |access-date=2023-11-26}}</ref><ref>{{Cite web |last=Albon |first=Courtney |date=June 9, 2023 |title=Space Force sees further delays to 'troubled' GPS ground segment |url=https://www.c4isrnet.com/battlefield-tech/space/2023/06/09/space-force-sees-further-delays-to-troubled-gps-ground-segment/ |access-date=2023-11-26 |website=C4ISRNet |language=en}}</ref> In late 2023, Frank Calvelli, the assistant secretary of the Air Force for space acquisitions and integration, stated that the project was estimated to go live some time during the summer of 2024.<ref>{{Cite web |last=Hitchens |first=Theresa |date=November 7, 2023 |title=Next-gen GPS ground system expected to come online this summer: Calvelli |url=https://breakingdefense.com/2023/11/next-gen-gps-ground-system-expected-to-come-online-this-summer-calvelli/ |access-date=2025-03-15 |website=Breaking Defense |language=en-US }}</ref>