Space Segment
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The GPS space segment consists of a constellation of satellites transmitting radio signals to users.
The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time.
To ensure this commitment, the Air Force has been flying 31 operational GPS satellites for the past few years.
Constellation Arrangement
GPS satellites fly in medium Earth orbit (MEO) at an altitude of approximately 20,200 km (12,550 miles). Each satellite circles the Earth twice a day.
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Expandable 24-Slot satellite constellation, as defined in the SPS Performance Standard.
The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Each plane contains four "slots" occupied by baseline satellites. This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet.
The Air Force normally flies more than 24 GPS satellites to maintain coverage whenever the baseline satellites are serviced or decommissioned. The extra satellites may increase GPS performance but are not considered part of the core constellation.
Current and Future Satellite Generations
The GPS constellation is a mix of old and new satellites. The following table summarizes the features of the current and future generations of GPS satellites, including Block IIA (2nd generation, "Advanced"), Block IIR ("Replenishment"), Block IIR-M ("Modernized"), Block IIF ("Follow-on"), GPS III, and GPS IIIF ("Follow-on").
Legacy Satellites | Modernized Satellites | |||
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Block IIA | Block IIR | Block IIR-M | Block IIF | GPS III/IIIF |
0 operational |
8 operational |
7 operational |
12 operational |
3 operational |
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As of November 13, 2020, there were a total of 30 operational satellites in the GPS constellation, not including the decommissioned, on-orbit spares.
For more up-to-date constellation status information, visit the NAVCEN website. Go there
Recent Developments
GPS III
- Dec 1, 2020: GPS III SV04 received operational acceptance.
View Space Force news release - Nov 5, 2020: The Space Force and its partners successfully launched the fourth GPS III satellite into orbit.
View Space Force news release - Jun 30, 2020: The Space Force successfully launched the third GPS III satellite into orbit.
View Space Force news release - Jun 2020: The Space Force completed the core mate of the eighth GPS III satellite and named it "Katherine Johnson."
View Space Force news release - May 2020: The Space Force performed the first GPS III maneuver.
View Space Force news release - Apr 2020: The Space Force rescheduled the launch of the third GPS III satellite from April to June 2020.
View Space Force news release - Mar 2020: The Space Force accepted control of the second GPS III satellite.
View Space Force news release - Jan 2020: The Air Force set the first GPS III satellite as healthy and active to users.
View AF news release - Aug 2019: The Air Force successfully launched the second GPS III satellite into orbit.
View AF news release