Satellite navigation

Satellite navigation, also called satnav, is the use of satellites to help people find places or know where they are. A global navigation satellite system, or GNSS, can help anyone on Earth, whether on land, in the air, or at sea. The four main GNSS systems are the United States Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), China's BeiDou Navigation Satellite System (BDS), and the European Union's Galileo. There are also smaller systems, like Japan's Quasi-Zenith Satellite System (QZSS) and India's Indian Regional Navigation Satellite System (IRNSS, also called NavIC).

Satellite navigation devices can find their location very accurately, sometimes within a few centimeters. They do this by listening to time signals from satellites. These devices can help with many things, like guiding you to a new place, tracking something, or keeping time very precisely. They work even without phone service or the internet, though these can improve the information.

Each system uses satellites moving around Earth in special paths called orbits. These satellites are about 20,000 kilometers or 12,000 miles above us and they circle Earth about every twelve hours. This way, they can cover almost the whole planet and help anyone who needs to know their location.

Classification

Further information: GNSS augmentation

There are different types of satellite navigation systems. GNSS-1 includes older systems like GPS and GLONASS, along with extra tools to make them more accurate. These tools include satellite-based augmentation systems and ground-based augmentation systems. Examples are the Wide Area Augmentation System in the United States and the European Geostationary Navigation Overlay Service in Europe.

GNSS-2 refers to newer systems like the European Galileo system. These provide better accuracy for things like airplane navigation. They use specific frequencies called Upper L Band and Lower L Band. Some devices can use both and are called "Dual-band GNSS" devices.

There are four main global satellite navigation systems: GPS from the United States, GLONASS from Russia, BeiDou from China, and Galileo from the European Union. There are also smaller regional systems and tools to improve accuracy, like NAVIC in India and QZSS in Japan. Many devices can use more than one system at the same time.

History

Further information: GPS § History, GLONASS § History, GALILEO#History, and BeiDou § History

Long ago, people used radio signals from the ground to find their way. Systems like DECCA, LORAN, GEE, and Omega sent out radio pulses from known places. By measuring the time between these pulses, people could figure out where they were.

The first system that used satellites for navigation was called Transit. It was made by the US military in the 1960s. Transit worked by tracking how the frequency of signals from satellites changed as they moved. This change, known as the Doppler effect, helped receivers know their location relative to the satellites. Scientists found ways to make the system more accurate for navigation.

Principles

Further information: GPS § Principles, and GPS § Navigation equations

Satellite navigation uses signals from satellites to find where you are. Each satellite sends out information about its location and the exact time it sent the signal. Your device can tell how far away each satellite is by measuring how long it took the signal to arrive. By looking at several satellites, the device can find your exact spot on Earth.

These systems need very accurate clocks, and they use special timekeeping devices on the satellites to stay in sync. Modern devices can use signals from many different satellite systems to get better results.

Applications

Main article: GNSS applications

Further information: Automotive navigation system

Satellite navigation was first made for use by the military. It helps guide things very accurately.

Today, systems like Galileo help people find where they are and where other places or things are, anywhere in the world. Satellite navigation has many uses, such as in science, transport, and farming.

Global navigation satellite systems

GPS (1978)

Main article: Global Positioning System

The United States' Global Positioning System (GPS) uses satellites to help people find their way. These satellites orbit Earth. GPS has been helping people since 1978 and is available all over the world. It is the most widely used system for finding locations.

GLONASS (1982)

Main article: GLONASS

GLONASS is a satellite system used mainly in Russia. It has been providing service since 1995 and uses satellites to cover the whole world.

BeiDou (2000)

Main article: BeiDou Navigation Satellite System

BeiDou started as a system for Asia and the Pacific. It grew over time, and by the end of 2018, it could serve the entire world. The last part of the system was finished in June 2020.

Galileo (2011)

Main article: Galileo (satellite navigation)

The European Union and the European Space Agency created Galileo as an alternative to GPS. It became fully working in December 2016. Galileo uses satellites and works together with GPS to give more accurate location information. The last satellite was launched in December 2021.

Regional navigation satellite systems

NavIC

Main article: NavIC

NavIC, or Navigation with Indian Constellation, is a regional satellite navigation system made by the Indian Space Research Organisation. The Indian government started this project in May 2006. It uses seven satellites—three in geostationary orbit (GEO) and four in geosynchronous orbit (GSO). This helps cover a larger area with fewer satellites. NavIC can give very accurate positions across India and a surrounding region.

By 2018, NavIC was ready for public use. It offers two types of service: one open for everyone and another special service for authorized users. India plans to grow NavIC by adding more satellites.

Early BeiDou

Main articles: BeiDou-1 and BeiDou-2

China's BeiDou system had its first two versions made to work well in certain areas.

Augmentation

GNSS augmentation makes navigation systems more exact and reliable by adding extra information. Examples include the Wide Area Augmentation System, the European Geostationary Navigation Overlay Service, the Multi-functional Satellite Augmentation System, Differential GPS, GPS-aided GEO augmented navigation, and inertial navigation systems.

QZSS

Main article: Quasi-Zenith Satellite System

The Quasi-Zenith Satellite System (QZSS) is a regional system to improve GPS in Japan and the Asia-Oceania areas. It began trial services in January 2018 and official services later that year. The first satellite was launched in September 2010, and a full system with 7 satellites is planned for 2023.

Comparison

See also: GPS signals, GLONASS signals, Galileo signals, and BeiDou signals

Using more than one satellite system helps you find your location faster and more accurately. The newest part of the BeiDou system was still being set up, so it was not as precise as the others yet.

Related techniques

Further information: Satellite geodesy § Radio techniques

DORIS

Main article: DORIS (satellite system)

DORIS is a French system that helps with very exact navigation. It uses special stations on Earth to send signals up to satellites. This helps scientists know exactly where the satellites are. This system can also be used on the ground, but it does not cover as much area as other systems. When used together with other navigation systems, it can help find positions even more accurately.

LEO satellites

The two current operational low Earth orbit (LEO) satellite phone networks can follow special devices and know where they are within a few kilometres. They do this by measuring how the satellite’s signal changes. The information can be shown on a screen or used to control certain phone features based on location.

International regulation

The International Telecommunication Union (ITU) defines a radionavigation-satellite service (RNSS) as a special service used for navigation from space. This service is important for safety and must be protected.

There are special types of this service for use on airplanes and ships. These help planes and ships find their way accurately using satellites.

Examples of these satellite navigation systems include BeiDou Navigation Satellite System, GALILEO, Global Positioning System, and GLONASS.

Alternatives

Alternative Positioning, Navigation and Timing (AltPNT) are other ways to find your location without using satellites. Some of these ways include:

• Inertial navigation systems (INS)
• eLORAN
• Terrain-based navigation (TBN)
• Visual Positioning Systems (VPS)
• LiDAR