Global Positioning System

The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide geolocation and time information to a GPS receiver anywhere on or near the Earth where signal quality permits.

GPS is very important because it helps people and machines know exactly where they are. This is useful for many things, like finding your way in a car, tracking where ships are on the ocean, or even helping farmers plant crops. It does not need the user to send any information out, and it works without phone or internet service, although those can make GPS even better.

Although the United States government created, controls, and maintains GPS, it is freely accessible to anyone with a GPS receiver. This means people all around the world can use it for many different purposes, from military operations to everyday activities like hiking or flying airplanes.

Overview

The GPS project started in 1973 by the U.S. Department of Defense. The first test satellite flew in 1978, and the full system of 24 satellites began working in 1993. At first, GPS for everyday use was only about 100 meters accurate, but it got better over time. By 2000, it was about 5 meters accurate, and new satellites are even more precise.

Today, many GPS devices, like those in smartphones, can be very accurate—sometimes within a few meters—especially when they use extra help from services like Wi-Fi positioning. As of March 2026, 21 satellites are sending out advanced signals, and they plan to have all 24 by 2027.

History

The GPS project started in the United States in 1973 to make navigation better. The U.S. Department of Defense made it, using 24 satellites, and it was ready to use in 1993. At first, it was only for the military, but people could start using it for other things in the 1980s. Important inventors include Roger L. Easton, Ivan A. Getting, Bradford Parkinson, and Gladys West.

GPS was built using ideas from older systems like LORAN and the Decca Navigator System. It fixes timing issues using a theory by Einstein, which helps it give exact locations. The system was also made to help the United States keep safe during the Cold War.

Principles

GPS satellites carry very stable atomic clocks that are synchronized with clocks on the ground. These clocks help find the distance between the satellites and the ground stations.

Each satellite sends out its own position and time information. A GPS receiver uses signals from at least four satellites to find its own location. It can tell where you are on Earth, how high up you are, and the time. This works because the speed of the signals is constant. By measuring tiny time differences, the receiver can find its exact spot. Modern satellites are being updated to give even better information for everyone using GPS.

Structure

The Global Positioning System (GPS) has three main parts: the space segment, the control segment, and the user segment. The U.S. Space Force manages the space and control parts. GPS satellites broadcast signals that help GPS receivers learn their location and time.

The space segment has 24 to 32 satellites orbiting Earth. These satellites follow paths called orbits, so there are always a few visible from anywhere on Earth. The control segment watches these satellites and keeps their clocks very accurate. The user segment includes everyone and everything that uses GPS, from military tools to everyday items like phones and car navigation systems. These devices use antennas and special clocks to catch the satellite signals and show where they are.

Applications

Main article: GNSS applications

GPS is a helpful tool that assists people in many ways. It was first created for use by the military, but now it has many everyday uses too.

GPS helps with daily activities. It gives very accurate time, which is important for things like banking, mobile phones, and power grids. People use GPS to find locations, track movements, and do many other tasks.

Some common uses of GPS include helping cars drive without a driver, letting people find their way with maps, and even in games like geocaching. It is also used in science to study the atmosphere and in weather forecasting.

Communication

Main article: GPS signals

GPS satellites send out special signals that help receivers know where they are. These signals tell the receiver where the satellite is and the time. The signals use two main frequencies that all satellites share. There are two types of signals: one for everyday users and one for the military.

Each satellite sends a long message that takes about 12 and a half minutes to finish. This message is split into smaller parts. It includes the satellite’s exact position and information about all satellites. GPS receivers use these signals to find their own location by listening to several satellites at once. The system uses special codes so receivers can tell each satellite’s signal apart, even though they all send on the same frequencies.

Navigation equations

Further information: GNSS positioning calculation

See also: Pseudorange

The Global Positioning System (GPS) uses signals from satellites to find out where on Earth you are. A GPS receiver listens to messages from satellites. These messages tell where the satellites are and what time it is. By comparing the time it receives these messages to its own clock, the receiver can work out how far away each satellite is.

To know your exact location, you need signals from at least four satellites. This is because the receiver’s clock isn’t as exact as the clocks on the satellites. With four or more satellites, the receiver can work out both where you are and how much its own clock is off. The more satellites you can receive signals from, the more exact your location will be.

Accuracy enhancement and surveying

The Global Positioning System (GPS) can be made more accurate with techniques like differential GPS. This uses extra ground stations to fix small errors in satellite signals. It helps experts measure distances and positions very precisely. This is important in work like land surveying, construction, and scientific research where exact locations are needed.

Regulatory spectrum issues concerning GPS receivers

In the United States, GPS receivers follow rules set by the Federal Communications Commission. These rules say that GPS devices must work even if they get interference from other signals. GPS devices are made to avoid picking up signals from nearby frequency bands.

The Federal Communications Commission allowed a company called LightSquared to use frequencies close to those used by GPS. This caused worries that LightSquared’s signals might interfere with GPS. In 2012, the FCC decided to stop LightSquared’s plan because it could disturb GPS signals. This decision was made after talks with other government groups that use GPS, like the United States Defense Department and Federal Aviation Administration.

Similar systems

Main article: Satellite navigation

After the United States created GPS, other countries made their own systems to help people find their way. Russia made GLONASS, which now works all around the world. China created the BeiDou system, which finished growing in 2020. Europe built Galileo, which started in 2016 and keeps growing. Japan has a system called QZSS to make GPS even better in Asia and the Pacific. India also has its own system named NavIC.

Backup system

If space weather or an attack damages the GPS satellites, the United States does not have a land-based system to replace them. This could cause big problems for the U.S. economy. A system called eLoran has been suggested as a backup, but it is not yet approved or funded.

China still uses a system called LORAN-C, and Russia has a similar system called CHAYKA ("Seagull").