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GPS, Galileo and BeiDou stay available through coordinated ground operations, monitoring, redundancy and satellite replacement—not by satellites maintaining themselves. Their operators track spacecraft and signals, manage orbital positions, address anomalies and plan for service continuity. The systems use different control arrangements, and the available public figures describe different dates and contexts, so they should not be read as a live, like-for-like inventory comparison.
How the three maintenance systems compare
| Maintenance dimension | GPS | Galileo | BeiDou |
|---|---|---|---|
| Monitoring and control | Monitor stations send measurements to a master control station, which monitors and commands satellites, resolves anomalies and can reposition them. | Separate Ground Control and Ground Mission segments handle spacecraft operations and navigation-system control; tracking stations communicate with satellites and sensor stations monitor navigation signals. | A multi-party response mechanism and a GNSS monitoring and assessment network check constellation status, signal accuracy and quality, and service performance. |
| Redundancy | The United States commits to at least 24 operational satellites 95% of the time; GPS normally operates more than 24 to support continuity during servicing or decommissioning. | ESA’s architecture description provides for one spare satellite in each of three orbital planes; it is a design description, not a live spare-availability report. | China’s official white paper describes backup satellites both in orbit and on the ground. |
| Planned intervention | The master control station handles satellite maintenance, anomaly resolution and repositioning. | The Ground Control Segment handles spacecraft housekeeping and constellation maintenance. The selected orbit is designed to avoid routine station-keeping after initial optimization. | An official notice documents planned annual upgrades and maintenance; an individual satellite can be marked unusable temporarily while work is underway. |
| Replenishment and retirement | Continuity is supported through successive satellite acquisitions and control-segment upgrades, alongside satellites beyond the 24-satellite baseline. | EUSPA manages operations and procures launch services for deployment and replenishment. ESA documents moving retired satellites to a higher safe orbit and passivating them. | The cited official material describes backup capacity and planned maintenance, but does not establish a comparable current replenishment schedule. |
What maintaining a satellite constellation involves
Maintenance is an end-to-end operational task. Ground teams observe spacecraft and navigation signals, use those observations to monitor system performance, command satellites, manage their orbital positions and respond to problems. Spare capacity matters because a satellite may be under maintenance, unavailable or approaching retirement while the overall service is expected to continue.
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That is different from maintaining a receiver. Phones, car navigation units and other GNSS user equipment receive or use signals; they do not command, repair or replenish the satellites. The control systems are institutional infrastructure.
How GPS is maintained
GPS’s control segment includes monitor stations distributed around the world and a master control station. GPS.gov describes 17 monitor-station sites. The stations use sophisticated GPS receivers to track satellites and collect navigation signals, range and carrier measurements, and atmospheric data. The master control station uses those observations to calculate satellite positions, prepare navigation messages for upload, check broadcasts and system integrity, resolve anomalies, carry out satellite maintenance and reposition satellites when needed.
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The baseline GPS arrangement has six orbital planes with four slots in each. The U.S. commitment is to maintain at least 24 operational satellites 95% of the time. GPS.gov says the Space Force normally flies more than 24 so service can continue when baseline satellites are serviced or decommissioned. GPS.gov reported 31 operational satellites, excluding decommissioned on-orbit spares, as of July 3, 2023. That is a dated count, not a current inventory.
Keeping GPS available does not mean replacing each satellite as soon as it reaches a nominal design life. Continuity comes from operating and managing the constellation, retaining satellites beyond the baseline, acquiring successive satellite blocks and modernizing the ground control system.
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How Galileo is maintained and replenished
ESA divides Galileo ground responsibilities between two segments. The Ground Control Segment manages spacecraft housekeeping and constellation maintenance; the Ground Mission Segment controls the navigation system. A global network of telemetry, tracking and command stations maintains contact with satellites, while Galileo sensor stations monitor navigation signals.
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ESA’s architecture description specifies three orbital planes, with a spare satellite in each plane. It says moving a spare into the position of a failed satellite could take days, compared with many months to arrange a new launch. The page also describes orbital-position tolerances and an orbit selected to avoid routine station-keeping maneuvers after a satellite’s initial optimization. These are architecture details, not confirmation that a particular spare is currently available.
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Replenishment includes both launching new spacecraft and retiring old ones. ESA reported in 2025 that GSAT0104 became the first Galileo satellite to be decommissioned after 12 years of service, mostly in Search and Rescue. ESA says an end-of-service satellite is moved to a higher safe orbit and passivated by depleting its energy sources. EUSPA is responsible for Galileo operational management and for procuring launch services needed for deployment and replenishment.
How BeiDou is maintained
China’s BeiDou white paper presents reliability as a coordinated responsibility spanning space, ground and user segments. It describes a multi-party response mechanism, a GNSS monitoring and assessment network that checks constellation status, signal accuracy, signal quality and service performance, and backup satellites both in orbit and on the ground.
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- Road trip–ready features include the HISTORY database of notable sites, a U.S. national parks directory, Tripadvisor traveler ratings and millions of Foursquare POIs
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A specific official notice illustrates planned work: it describes annual upgrades and maintenance of on-orbit BDS-3 satellites. During the process, an individual satellite may be set to unusable for a period; the notice says BeiDou service-performance indicators remained in line with the Open Service Performance Standard. The operation began May 31, 2021, and the notice was published June 1, 2022. It is a historical example, not a current maintenance schedule.
BeiDou uses a mixed-orbit constellation, unlike the GPS and Galileo baseline layouts. Its chips, modules, antennas, boards and receivers are user products: they receive or use the service and are not equipment for commanding or maintaining the constellation.
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- View food, fuel and rest areas along your active route, and see upcoming cities and milestones
- View Tripadvisor traveler ratings for top-rated restaurants, hotels and attractions to help you make the most of road trips
- Directory of U.S. national parks simplifies navigation to entrances, visitor centers and landmarks within the parks
What happens when a satellite fails or needs work?
The exact response depends on the system and event, but the general continuity strategy is to detect and assess the issue, manage the affected satellite, and rely on available capacity elsewhere in the constellation where possible. GPS’s control segment can resolve anomalies and reposition satellites. ESA’s Galileo architecture describes moving a spare into a failed satellite’s position, while BeiDou’s official white paper describes in-orbit and ground backup capacity. BeiDou’s maintenance notice also shows that planned work can temporarily make one satellite unusable while stated service indicators remain within the service standard.
These examples do not establish identical failure procedures, spare availability or service outcomes across all three systems. Public descriptions differ in scope and date.
Why satellite counts and maintenance claims need dates
A satellite count is meaningful only with its date and definition: operational spacecraft, on-orbit spares and decommissioned satellites are not interchangeable categories. GPS.gov’s figure of 31 operational satellites applies to July 3, 2023, while its minimum commitment and usual practice describe different things. ESA’s Galileo page describes architecture rather than a current spacecraft-status list. The BeiDou material cited here is an older white paper and a historical maintenance notice, not a current inventory.
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