How do we determine our exact location anywhere on Earth with pinpoint accuracy? The answer lies in the Global Positioning System (GPS), a US government satellite-based navigation radio-navigation system that provides precise positioning, navigation, and timing (PNT) services to users worldwide, regardless of weather conditions.
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GPS works through a network of satellites that send navigation signals, supported by ground and satellite control stations that monitor and manage the system. It plays a vital role in everyday life, from navigation and clock synchronization to supporting disaster response efforts.
This article will explore how GPS works, breaking down its three main segments. We will also look to discuss GPS accuracy, its various applications across industries, and its ongoing advancements in reliability and precision. So, shall we get started?
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So, How Does GPS Really Work?
The GPS system is a network of orbiting satellites that provides accurate positioning, navigation, and timing data to military and civilian users worldwide. It is managed and operated by Space Delta 8 at Schriever Air Force Base in Colorado. The system is structured into three main segments:
- The Space Segment: A group of satellites transmitting navigation signals.
- The Control Segment: A network of ground stations managing and monitoring the satellites.
- The User Segment: GPS receivers interpret the signals to determine position and time.
The US Space Force is responsible for developing, maintaining, and operating the space and control segments.
The Space Segment
The space segment is made up of 24 satellites, each transmitting one-way radio signals that provide GPS time and position data. To keep coverage reliable, the US ensures that at least 24 satellites are active at least 95 % of the time. In reality, though, the US Space Force has been flying 31 satellites for over a decade to maintain this standard.
These satellites orbit the Earth at an altitude of 20,200 km (12,550 miles), circling the planet twice a day while constantly sending out navigation signals. They’re arranged in six evenly spaced orbital planes, with each plane containing four satellite slots. This setup guarantees that users, no matter where they are, can always receive signals from at least four satellites—enough to determine location, velocity, and time when using the right equipment.
To keep GPS running smoothly, the Space Force typically flies more than 24 satellites, adding extras when older ones are retired or serviced. While these additional satellites improve GPS performance, they aren’t officially part of the core constellation.
In 2011, the US Air Force introduced the 'Expandable 24' configuration, repositioning six satellites and expanding three of the 24 slots. This tweak increased the constellation to 27 satellites, boosting GPS performance and global coverage. Today, GPS functions as a 27-slot system.
Of all the operational GPS satellites, the six GPS III/IIIF models are the most advanced. First launched in 2018, these satellites provide better signal reliability, accuracy, and integrity. They also have a 15-year design lifespan and do not use selective availability.4,5
The Control Segment
The control segment is a worldwide network of ground facilities responsible for tracking GPS satellites, monitoring their transmissions, analyzing performance, and sending commands.
Currently, this network includes 16 monitoring sites, 11 command and control antennas, a master control station (MCS), and an alternate master control station (AMCS). The monitor stations:
- Collect range/carrier measurements, atmospheric data, and navigation signals
- Use advanced GPS receivers
- Send observations to the MCS
- Provide worldwide coverage with 16 sites
- Track GPS satellites as they pass overhead
The MCS then processes the data from monitoring stations to calculate precise satellite locations. It manages command and control for the entire constellation, ensuring accuracy and system integrity. It also generates navigation messages that are uploaded to satellites and oversees maintenance, repositioning satellites as needed to optimize performance. Different systems are used to control operational and non-operational satellites.
Ground antennas play a key role by collecting telemetry and communicating via the S-band. They assist with early orbit support, anomaly resolution, navigation data uploads, processor program loads, and other command transmissions.6
The User Segment
The user segment consists of GPS receivers that pick up signals from satellites and use the information to determine the user’s 3D position and time.3
Most GPS receivers include:
- An antenna with anti-jamming capabilities to pick up the signal
- A receiver-processor that converts the radio signal into location data
- A control/display unit that shows positioning details and lets users manage settings
GPS receivers work by detecting signals from multiple orbiting satellites. Each satellite transmits a unique signal containing its location and the exact time it was sent. The receiver’s antenna then picks up these signals and calculates the distance to each satellite based on how long the signal took to arrive.8
Using a method called trilateration, the receiver processes signals from at least four satellites to pinpoint its exact position in three dimensions: latitude, longitude, and altitude. The data is then processed and displayed, giving the user real-time location, speed, and time.
Check out the below video from the Federal Aviation Administration that breaks down how GPS really works:
GPS How It Works
How Accurate is GPS?
GPS accuracy is critical for everything from navigation and transportation to emergency response and scientific research. Inaccurate positioning can lead to inefficiencies, safety risks, and even life-threatening situations—whether it’s a first responder trying to locate an emergency, a self-driving car navigating city streets, or a surveyor mapping land boundaries with precision.
The US government commits to broadcasting GPS signals in space with a daily global average user range error (URE) of ≤2.0 m with 95 % probability across all operational satellites within constellation slots. Actual performance often exceeds this, with the global average URE recorded at ≤0.643 m on April 20, 2021, across all satellites.9
However, URE reflects signal accuracy in space—not the accuracy experienced by users on the ground. User accuracy depends on several factors, including URE, satellite geometry, signal blockage, atmospheric conditions, and receiver quality.
For instance, GPS-enabled smartphones typically provide accuracy within a 4.9-meter radius in open sky conditions. However, their performance declines in areas with obstructions like bridges, trees, and buildings, which can block satellite signals.
High-precision applications rely on augmentation systems and dual-frequency receivers to improve GPS accuracy. These advanced systems enable long-term measurements at the millimeter level and real-time positioning within just a few centimeters.9
What are the Applications of GPS?
GPS is used for a wide range of applications, both in space and here on Earth. While NASA and other space agencies leverage GPS for research, communications, and navigation beyond our planet, GPS is also an essential tool for industries, businesses, and everyday life.
GPS in Space
In space, GPS plays a key role in improving spacecraft autonomy, enhancing communications, and supporting scientific research. Satellites and spacecraft rely on the Deep Space Network (DSN) and Near Space Network (NSN) to determine their position and time. In Low Earth Orbit (LEO) and beyond, some missions also use GPS signals as a backup or additional data source for trajectory tracking, with usability now extending all the way to Geosynchronous Orbit (GEO).
Traditionally, spacecraft have depended on ground-based tracking stations for navigation. However, more missions are turning to GPS for onboard positioning, reducing reliance on NASA’s tracking infrastructure. By processing GPS signals directly, spacecraft can calculate their position and time in real time, making operations more efficient and unlocking new possibilities for spaceflight.
Beyond navigation, GPS is also a powerful tool for science. It helps researchers study shifts in the Earth’s gravity field, rising sea levels, and melting ice caps. NASA, in collaboration with agencies like the National Space-based Positioning, Navigation, and Timing (PNT) Executive Committee, is working on improvements to GPS accuracy for scientific applications. One promising project involves adding laser retro-reflectors to next-generation GPS satellites, which could refine Earth’s reference frame to millimeter-level accuracy—an upgrade that would significantly enhance climate monitoring and geophysical studies.
NASA is also using GPS to make spacecraft more self-sufficient. Alongside other Global Navigation Satellite Systems (GNSS), like Russia’s GLONASS and Europe’s Galileo, GPS allows spacecraft to navigate autonomously by processing one-way signals directly onboard. This improves trajectory tracking and enhances precision timing and orientation control without relying on additional sensors like star trackers.
To keep pushing GPS technology forward, NASA continues to develop high-precision GPS receivers for spaceflight and science missions. These advancements not only improve space navigation but also enhance Earth observation capabilities and ensure GPS remains a critical tool for future exploration.
GPS on Earth
On Earth, GPS is an essential tool for navigation, timing, and tracking across a wide range of industries.
In transportation and logistics, ride-sharing apps like Uber and Lyft depend on GPS for real-time tracking, while delivery companies use it to optimize routes and provide accurate arrival estimates. Airlines use GPS for navigation, and railways and shipping companies rely on it for precise scheduling and routing. In agriculture, GPS enables precision farming, allowing automated machinery to plant, monitor, and harvest crops with extreme accuracy, improving efficiency and reducing waste.
Public safety and emergency response also heavily rely on GPS. First responders use it to quickly locate emergencies, enhance search-and-rescue missions, and coordinate disaster relief efforts. GPS also plays a major role in construction and mining, where it guides heavy machinery for automated grading, excavation, and mapping, improving both safety and efficiency on worksites.
The finance and telecommunications industries depend on GPS for precise time synchronization, ensuring smooth transactions, stock market trades, and data transfers. Everything from ATMs to high-frequency trading systems and mobile networks relies on GPS for accurate timing. Even everyday activities, such as using a credit card or making a phone call, often involve GPS-based timekeeping.
Sports and fitness are another area where GPS has become indispensable. Athletes use GPS to track speed, distance, and performance, while wearable devices like smartwatches and fitness trackers rely on it for accurate activity monitoring. Professional sports teams use GPS for player tracking and performance analysis, gaining insights into movement patterns and conditioning.
Environmental science also benefits from GPS, helping researchers track weather patterns, monitor earthquakes, and study wildlife movements. Scientists use GPS to analyze deforestation, monitor climate change, and study ocean currents, providing crucial data for conservation efforts.
From guiding spacecraft to optimizing everyday tasks, GPS has become an essential part of modern life. Whether it's improving transportation, enhancing public safety, advancing scientific research, or powering financial systems, GPS continues to evolve, keeping the world more connected, efficient, and informed.
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References and Further Reading
- Satellite Navigation - Global Positioning System (GPS) [Online] Available at https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gnss/gps (Accessed on 03 February 2025)
- GPS [Online] Available at https://www.nasa.gov/directorates/somd/space-communications-navigation-program/gps/ (Accessed on 03 February 2025)
- The Global Positioning System [Online] Available at https://www.gps.gov/systems/gps/ (Accessed on 03 February 2025)
- Space Segment [Online] Available at https://www.gps.gov/systems/gps/space/ (Accessed on 03 February 2025)
- Global Positioning System [Online] Available at https://www.spoc.spaceforce.mil/About-Us/Fact-Sheets/Display/Article/2381726/global-positioning-system (Accessed on 03 February 2025)
- Control Segment [Online] Available at https://www.gps.gov/systems/gps/control/ (Accessed on 03 February 2025)
- Mahato, S. Introduction To GPS [Online] Available at https://dspmuranchi.ac.in/pdf/Blog/GPS.pdf (Accessed on 03 February 2025)
- Trilateration Exercise [Online] Available at https://www.gps.gov/multimedia/tutorials/trilateration/ (Accessed on 03 February 2025)
- GPS Accuracy [Online] Available at https://www.gps.gov/systems/gps/performance/accuracy/ (Accessed on 03 February 2025)
- GPS Applications [Online] Available at https://www.gps.gov/applications/
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