Control Segment

Map showing the master control station at Schriever AFB, Colorado; alternate master control station at Vandenberg AFB, California; ground antennas in Cape Canaveral, Ascension, Diego Garcia, and Kwajalein; AFCSN remote tracking stations in Hawaii, Vandenberg AFB, New Hampshire, Greenland, United Kingdom, Diego Garcia, and Guam; Air Force monitoring stations in Hawaii, Schriever AFB, Cape Canaveral, Ascension, Diego Garcia, and Kwajalein; and NGA monitoring stations in Alaska, Ecuador, USNO, Uruguay, United Kingdom, South Africa, Bahrain, South Korea, Australia, and New Zealand

The GPS control segment consists of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation.

The current operational control segment includes a master control station, an alternate master control station, 11 command and control antennas, and 16 monitoring sites. The locations of these facilities are shown in the map above. Download as PDF (113 KB)

Air Force Personnel: Team Blackjack

Air Force video: 2SOPS keeps GPS flying! (2009)

Team Blackjack mission patch The GPS constellation delivers consistently high performance thanks to the dedicated efforts of its operators — the men and women of the U.S. Air Force's 2nd Space Operations Squadron (2SOPS) and the Air Force Reserve's 19th Space Operations Squadron (19SOPS) at Schriever Air Force Base, Colorado.

Together, 2SOPS and 19SOPS — nicknamed Team Blackjack — keep the GPS satellites flying on a 24/7 basis, with continuous availability and high accuracy for billions of civilian and military users.

Learn more at

Control Segment Elements

Master Control Station (MCS)

2SOPS officers at workstation The master control station in Colorado is where 2SOPS performs the primary control segment functions, providing command and control of the GPS constellation. The MCS generates and uploads navigation messages and ensures the health and accuracy of the satellite constellation. It receives navigation information from the monitor stations, utilizes this information to compute the precise locations of the GPS satellites in space, and then uploads this data to the satellites.

The MCS monitors navigation messages and system integrity, enabling 2SOPS to determine and evaluate the health status of the GPS constellation. 2SOPS uses the MCS to perform satellite maintenance and anomaly resolution. In the event of a satellite failure, the MCS can reposition satellites to maintain an optimal GPS constellation.

Monitor Stations

Monitor stations track the GPS satellites as they pass overhead and channel their observations back to the master control station. Monitor stations collect atmospheric data, range/carrier measurements, and navigation signals. The sites utilize sophisticated GPS receivers and are operated by the MCS.

There are 16 monitoring stations located throughout the world, including six from the Air Force and 10 from the National Geospatial-Intelligence Agency (NGA).

Ground Antennas

GPS ground antenna Ground antennas are used to communicate with the GPS satellites for command and control purposes. These antennas support S-band communications links that send/transmit navigation data uploads and processor program loads, and collect telemetry. The ground antennas are also responsible for normal command transmissions to the satellites. S-band ranging allows 2SOPS to provide anomaly resolution and early orbit support.

There are four dedicated GPS ground antenna sites co-located with the monitor stations at Kwajalein Atoll, Ascension Island, Diego Garcia, and Cape Canaveral. In addition, the control segment is connected to the seven Air Force Satellite Control Network (AFSCN) remote tracking stations worldwide, increasing visibility, flexibility, and robustness for telemetry, tracking, and command.

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Control Segment Modernization

As part of the GPS modernization program, the Air Force has continuously upgraded the GPS control segment over the past few years and will keep doing so in the years to come. Learn more about GPS Modernization

Next Generation Operational Control System (OCX)

Raytheon video: GPS OCX Modernization (2014)

The Next Generation Operational Control System is the future version of the GPS control segment.

The OCX system will command all modernized and legacy GPS satellites, manage all civil and military navigation signals, and provide improved cybersecurity and resilience for the next generation of GPS operations.

The OCX program includes the following phases: 

Recent Developments

More Information

Launch Checkout Capability (LCC)

The Launch Checkout Capability is a command and control center that will checkout all GPS III satellites. Unlike today's LADO system, which operates separately from the master control station, the LCC will be fully integrated with OCX. This approach will allow the operation of a single OCX-centric system that can sustain the GPS constellation from launch to disposal.

The LCC component of OCX will be delivered prior to OCX Block 1 in order to support the launch and checkout of the first GPS III satellite. The LCC will ensure a timely launch so constellation availability remains optimal and not impacted by the late discovery of problems.

The Air Force awarded the contract for the provision of the LCC to Lockheed Martin in January 2012. View contractor's press release

At the same time, the Air Force awarded Raytheon a contract for the development of the Launch and Checkout System (LCS), a component of the LCC. View contractor's press release

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Past Upgrades

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