Maarg Manthan · Topic 12.6

Navigation Satellite Systems: GPS, Galileo, GLONASS, NavIC (IRNSS), GAGAN

Science & Technology › Space Technology and ISRO · Topic 12.6

A satellite navigation system uses a group of satellites that send timed radio signals so that a receiver can work out its position, speed and the exact time. A receiver needs signals from at least four satellites to find its three position coordinates and correct its clock error. The global systems are the Global Positioning System of the United States, GLONASS of Russia, Galileo of the European Union and BeiDou of China. India's regional system is NavIC, meaning Navigation with Indian Constellation, also called IRNSS, which covers India and a region up to 1,500 kilometres beyond its borders. GAGAN, the GPS Aided GEO Augmented Navigation system, is India's satellite based augmentation system that improves the accuracy of GPS signals for aircraft.

5 min read · UPSC Prelims · Science & Technology · Space Technology and ISRO

At a Glance

Global systems GPS, GLONASS, Galileo, BeiDou
Indian regional system NavIC
NavIC reach India plus 1,500 km
Augmentation system GAGAN
Minimum signals Four satellites
Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO

Where Does It Fit?

This topic follows the account of launch vehicles. Navigation satellites are among the most useful payloads that launchers carry, and India built its own system to reduce dependence on foreign signals. Previous topic: Launch Vehicle Technology: PSLV, GSLV and Cryogenic Engines. Next topic: Chandrayaan Missions (Chandrayaan-I, II, III) and the Mars Orbiter Mission.

System	Country and features
GPS	United States. Operated by the Space Force. About 31 operating satellites in medium Earth orbit at about 20,200 km. Fully operational in 1995. Free civil signal and encrypted military signal
GLONASS	Russia. 24 satellites in medium Earth orbit at about 19,100 km. Fully global by 2011
Galileo	European Union. Civilian control. About 28 satellites in medium Earth orbit, with initial services from 15 December 2016. Accuracy in the metre range
BeiDou	China. Global coverage declared complete in 2020 with a mix of orbits. Provides short messaging too
NavIC (IRNSS)	India. Seven satellite design of geostationary and inclined geosynchronous satellites. Coverage India plus 1,500 km. Standard Positioning Service and encrypted Restricted Service
QZSS	Japan’s regional system, Quasi-Zenith Satellite System, for Japan and the Asia-Oceania region
GAGAN	India. GPS Aided GEO Augmented Navigation, built by the Airports Authority of India with ISRO. Uses GSAT satellites and ground stations to correct GPS

How Do These Systems Work and Where Are They Used?

Trilateration: each satellite sends its position and time, and a receiver finds its distance from at least three, then uses a fourth to correct its own clock
Atomic clocks: satellites carry very precise clocks, since a time error of one microsecond is a ranging error of about 300 metres
Relativity correction: satellite clocks run at slightly different rates from clocks on the ground and are corrected to keep accuracy
Differential methods: augmentation systems use ground stations at known locations to find errors and broadcast corrections
Aviation: GAGAN helps aircraft to make precise approaches and was certified for use in civil aviation in 2013 and for approach with vertical guidance in 2015
Rail and road: train tracking, vehicle tracking and emergency response
Fisheries and disaster warning: NavIC provides messages to fishermen at sea and alerts during disasters
Timing: banks, power grids and mobile networks use satellite time signals

What Else Should You Remember?

NavIC satellites: IRNSS-1A to 1G were launched between 2013 and 2016. Some early atomic clocks failed, and replacement NVS satellites with new clocks and an additional L1 band started in 2023
NVS series: NVS-01 was launched in May 2023 on GSLV-F12, and an NVS-03 satellite was launched on a GSLV in late October 2026 to restore a minimum working constellation, according to reports
L5 and S bands: NavIC signals are in the L5 and S bands, giving better resistance to ionospheric error
Accuracy: NavIC is expected to give position accuracy better than 20 metres over India, and better near 5 to 10 metres in practice for many receivers
Mobile support: some phone chipsets support NavIC, but wide use depends on a complete constellation
Kargil lesson: during the 1999 Kargil conflict, India had no assured access to GPS data for the area, which is cited as a reason for a national system
Strategic importance: foreign systems can be degraded in a crisis, so an own system gives autonomy
Link with ISRO series: NavIC satellites are covered in ISRO’s Space Research Programme and ANTRIX Corporation as part of the national space effort
Software defined receivers: receivers that use many systems together give better position fixes in cities
GAGAN and GPS: GAGAN depends on GPS signals and improves their accuracy, while NavIC is an independent system
Counting satellites: exam answers should say that exact satellite counts change as old satellites retire and new ones are launched
Space weather: solar storms disturb the ionosphere, so dual frequency receivers help to correct signal delays

Why Does It Matter for the Exam?

Systems and owners: GPS US, GLONASS Russia, Galileo EU, BeiDou China
NavIC details: coverage 1,500 km, services SPS and RS
GAGAN: augmentation for aviation
Current affairs link: NVS satellites and mobile support
Common errors: calling GAGAN an independent system, or Galileo a military system

As an analytical point, a regional system gives India control over a critical service, but it becomes useful only when satellites are complete and phones and devices use it widely.

Why Is This Topic Important?

Systems Who owns what
NavIC India’s own
GAGAN Aviation support

What Came Next?

The next topic covers the Chandrayaan missions and the Mars Orbiter Mission. Next topic: Chandrayaan Missions (Chandrayaan-I, II, III) and the Mars Orbiter Mission.

Key People and Terms

GNSS Global navigation satellite system
RNSS Regional navigation satellite system
SBAS Satellite based augmentation system
SPS Standard positioning service
RS Restricted service
PNT Position, navigation, timing

Exam Corner

Points to Remember

Minimum signals needed: four.
NavIC coverage: India plus 1,500 km.
Galileo is under civilian control.
GAGAN = augmentation, not independent.
GPS height: about 20,200 km.

Do Not Confuse With

NavIC and GAGAN Independent regional system versus GPS correction system
GPS and GNSS One US system versus all global systems
SPS and RS Open service versus encrypted service

Memory Hook

GPS America, GLONASS Russia, Galileo Europe, BeiDou China; NavIC for India, GAGAN to guide the air.

Mains Angle

Questions ask to match systems with owners and features. These points help.

Need Strategic autonomy
Status NavIC and GAGAN
Gaps Constellation and devices

A Question You May Face

An original practice question, not a past paper question.

“Discuss the importance of NavIC and GAGAN for India and the challenges in making the national navigation system widely used.”

How to Answer

Systems Global versus regional.
India NavIC, GAGAN.
Challenges Satellites, devices.
Way Complete constellation.

GS Relevance

Prelims: global and regional systems, NavIC details, GAGAN, number of satellites. GS Paper 3: science and technology, space applications.

Frequently Asked Questions

What is NavIC?

NavIC, short for Navigation with Indian Constellation and earlier called IRNSS, is India's regional satellite navigation system. It covers India and a region extending about 1,500 kilometres beyond its borders, and offers a Standard Positioning Service for all users and an encrypted Restricted Service for authorised users.

What is GAGAN?

GAGAN, the GPS Aided GEO Augmented Navigation system, is a satellite based augmentation system developed by the Airports Authority of India with ISRO. It uses ground reference stations and geostationary satellites to correct errors in GPS signals, so that aircraft can use GPS for safe approach and landing over the Indian region.

How many satellites are needed to find a position?

A receiver needs signals from at least four satellites. Three signals give the distance to three known points and so fix the position in three dimensions, while the fourth signal is used to correct the receiver's clock, which is much less precise than the atomic clocks on the satellites.

Which countries have global navigation satellite systems?

The United States has the Global Positioning System, Russia has GLONASS, the European Union has Galileo and China has BeiDou. Regional systems include India's NavIC and Japan's QZSS. All the global systems orbit in medium Earth orbit, at about 19,000 to 23,000 kilometres above the Earth.

Why did India build its own navigation system?

India built NavIC to have an independent source of positioning and timing, because foreign systems can be restricted or degraded during a crisis. The experience of the 1999 Kargil conflict, when access to GPS data for the area was not assured, is often cited as a reason for developing a national system.

PYQ Practice — Statement Analysis

1 Galileo is a navigation system operated by the European Union.

True

Under civilian control.

2 GAGAN is an independent navigation system that does not use GPS.

False

It augments GPS.

3 NavIC covers India and about 1,500 km beyond its borders.