A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS).
As of 2023, four global systems are operational: the United States’s Global Positioning System (GPS), Russia’s Global Navigation Satellite System (GLONASS), China’s BeiDou Navigation Satellite System, and the European Union’s Galileo.
Regional navigation satellite systems in use are Japan’s Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigation Satellite System (IRNSS) or NavIC, which is planned to be expanded to a global version in the long term.
Global navigation satellite systems
Global Positioning System (GPS)
The United States’ Global Positioning System (GPS) consists of up to 32 medium Earth orbit satellites in six different orbital planes. The exact number of satellites varies as older satellites are retired and replaced. Operational since 1978 and globally available since 1994, GPS is the world’s most utilized satellite navigation system.
GLObal NAvigation Satellite System or GLONASS
The formerly Soviet, and now Russian, Global’naya Navigatsionnaya Sputnikovaya Sistema, (GLObal NAvigation Satellite System or GLONASS), is a space-based satellite navigation system that provides a civilian radio navigation-satellite service and is also used by the Russian Aerospace Defence Forces. GLONASS has full global coverage since 1995 and with 24 active satellites.
BeiDou
BeiDou started as the now-decommissioned Beidou-1, an Asia-Pacific local network on the geostationary orbits. The second generation of the system BeiDou-2 became operational in China in 2011.
The BeiDou-3 system is proposed to consist of 30 MEO satellites and five geostationary satellites (IGSO). A 16-satellite regional version (covering Asia and Pacific area) was completed by 2012. Global service was completed by 2018. On 23 June 2020, the BDS-3 constellation deployment is fully completed after the last satellite was successfully launched at the Xichang Satellite Launch Center.
Galileo
The European Union and European Space Agency agreed in March 2002 to introduce their own alternative to GPS, called the Galileo positioning system. Galileo became operational on 15 December 2016 . The full Galileo constellation consists of 24 active satellites, the last of which was launched in December 2021.
Regional navigation satellite systems
NAVigation with Indian Constellation NavIC
The NavIC or NAVigation with Indian Constellation is an autonomous regional satellite navigation system developed by the Indian Space Research Organisation (ISRO). It consists of a constellation of 7 navigational satellites. Three of the satellites are placed in geostationary orbit (GEO) and the remaining 4 in geosynchronous orbit (GSO) to have a larger signal footprint and lower number of satellites to map the region.
It is intended to provide an all-weather absolute position accuracy of better than 7.6 metres throughout India and within a region extending approximately 1,500 km around it.
NavIC provides two levels of service, the “standard positioning service”, which will be open for civilian use, and a “restricted service” (an encrypted one) for authorized users (including military).
There are plans to expand NavIC system by increasing constellation size from 7 to 11. India plans to make the NAVIC global by adding 24 more MEO satellites.
Quasi-Zenith Satellite System (QZSS)
The Quasi-Zenith Satellite System (QZSS) is a four-satellite regional time transfer system and enhancement for GPS covering Japan and the Asia-Oceania regions.
PRACTICE QUESTIONS
QUES . Which one the following countries has its own Satellite Navigation System? UPSC 2023
(a) Australia
(b) Canada
(c) Israel
(d) Japan
Ans (d)
