Navigation Technology

Every navigation satellite sends out a radio signal. The signal carries the time it was sent and the satellite’s position. Your receiver notes when the signal arrives. The delay tells it how far away the satellite is.

Why are four satellites needed?

Think of each distance as a sphere around a satellite. You sit somewhere on that sphere.

• One satellite puts you on a sphere.
• Two satellites narrow you to a circle where two spheres meet.
• Three satellites leave only two points. One of them is your true position.
• A fourth satellite fixes the receiver’s clock and settles the doubt.

Satellites carry very exact atomic clocks. A phone or car receiver has only a cheap quartz clock. The fourth signal lets the receiver correct its own clock. So four satellites is the minimum for a reliable 3D fix.

What can disturb the signal?

The signals are very faint. The ionosphere can delay them by several metres. Receivers that listen on two frequencies can correct this error. NavIC also uses two frequency bands for this reason.

What does GNSS mean?

GNSS stands for Global Navigation Satellite System. It means any satellite group that gives worldwide position and time. NavIC and Japan’s QZSS are regional systems. They cover only a part of the world.

Four systems give worldwide cover. Each belongs to one country or group. Most of their satellites fly in medium Earth orbit, or MEO. Lower orbits would need more satellites. Higher orbits would cover less of the Earth.

What should you remember about each system?

• GPS belongs to the USA. NASA says the first satellite was launched in 1978. The US government counted 31 operational satellites in July 2023. They fly at about 20,200 km in six orbital planes.
• GLONASS belongs to Russia. Its first launch was in October 1982. It is designed for 24 satellites in three planes at about 19,100 km.
• Galileo belongs to the European Union. Its initial services began on 15 December 2016. ESA says the system has 28 satellites. They fly at about 23,222 km.
• BeiDou belongs to China. Its global system, BDS-3, was completed with a final launch on 23 June 2020. It has 24 MEO, 3 GEO and 3 IGSO satellites.

Is there a regional system apart from NavIC?

Yes. Japan runs QZSS, also called Michibiki. Its first satellite was launched on 11 September 2010. It complements GPS over Japan and the Asia-Oceania region. Japan is building it up to seven satellites.

ISRO built NavIC to give India its own position and time service. The name means Navigation with Indian Constellation. Its older name is the Indian Regional Navigation Satellite System, or IRNSS. NavIC is regional, not global.

What is the design?

• The design has 7 satellites and ground stations that work day and night.
• Three satellites sit in geostationary orbit, at 32.5°E, 83°E and 129.5°E.
• Four satellites sit in inclined geosynchronous orbit, with an inclination of 29°.
• All of them fly at about 36,000 km. GPS flies lower, at about 20,000 km.

How far does it reach?

NavIC covers India and a region up to about 1,500 km beyond its boundary. That region is its primary service area. Do not mix this up with an area. The reach is a distance.

What services does it give?

NavIC gives two services. The Standard Position Service is for civilians. The Restricted Service is for strategic users. ISRO says both services are provided in the L5 band and the S band. ISRO says position accuracy is better than 20 metres in the primary service area.

The newer NVS satellites add a civilian signal in the L1 band. NavIC signals can work together with GPS, GLONASS, Galileo and BeiDou signals.

The first NavIC satellite flew in July 2013. Seven satellites were up by April 2016. Later launches added a second generation.

What is the launch timeline?

• IRNSS-1A was launched in July 2013 by PSLV-C22. It was the first satellite of the system.
• IRNSS-1B, 1C and 1D followed in April 2014, October 2014 and March 2015.
• IRNSS-1E, 1F and 1G were launched on 20 January, 10 March and 28 April 2016. They completed the seven-satellite design.
• PSLV-C39 was to launch IRNSS-1H. ISRO says the mission was unsuccessful, and the satellite could not be placed in orbit.
• IRNSS-1I was launched on 12 April 2018. It was the eighth satellite to join the system.
• NVS-01 was launched on 29 May 2023 by GSLV-F12. It was the first of the second generation. It carried an Indian-made atomic clock for the first time.
• NVS-02 was launched on 29 January 2025 by GSLV-F15.

What went wrong with NVS-02?

NVS-02 reached its first elliptical orbit. The step that lifts it to its final circular orbit could not be carried out. ISRO’s committee found that the drive signal did not reach the pyro valve on the oxidiser line. ISRO’s report names the disengagement of contacts in the connector as the most likely cause. ISRO says it applied the fixes in the CMS-03 spacecraft.

Why does a clock matter so much?

NavIC works by exact time. When IRNSS-1F’s atomic clock stopped, ISRO said the satellite could only send one-way messages. NVS-01 flew an Indian-made atomic clock for the first time. NVS-02 carried a mix of Indian and procured clocks.

What does IRNSS-1A do today?

ISRO changed IRNSS-1A to send safety-of-life alerts. It warns fishermen about cyclones, tsunamis and high waves.

Government replies in Parliament give the latest picture. Eleven NavIC satellites have been launched. Eight were called functional in March 2026. But only some of them can give navigation.

What did the government say?

• In March 2026, Parliament was told that three satellites broadcast navigation signals. Five could send one-way messages.
• On 13 March 2026, the atomic clock of IRNSS-1F stopped. This satellite had completed its ten-year design life on 10 March.
• IRNSS-1F still sends one-way broadcast messages.
• In July 2026, the government named the three navigation satellites. They are IRNSS-1B, IRNSS-1I and NVS-01.
• It said the constellation cannot give standalone positioning, because four satellites are the minimum. The timing service still works.

Is anything coming next?

The government said NVS-03 is ready for launch. NVS-04 and NVS-05 are in an advanced stage. We found no ISRO launch page that gives a date. With NVS-03 the count would be four, which is the minimum.

Does this leave users stranded?

The government says there is no vulnerability for users. Most users use NavIC together with other systems. The Armed Forces use several systems together too.

What is the truth about the phone rule?

In 2023 a minister said 5G phones would need NavIC from 1 January 2025. In December 2025 the Department of Space told Parliament that the government had not mandated NavIC yet. Talks were still on. More than 60 phones already support it.

In 2023 the government said phone chips came from Qualcomm and Mediatek. Not every phone works with NavIC. The phone needs a compatible chipset.

Where is NavIC compulsory?

Vehicle trackers are different. The road transport ministry has made NavIC-based AIS-140 trackers compulsory for public and commercial vehicles.

Who uses NavIC?

• More than 10,000 trains carry NavIC-enabled tracking devices.
• More than 30,000 fishing vessels carry NavIC transponders.
• More than 15 lakh vehicles are fitted with certified trackers.
• Time receivers share Indian Standard Time across the country.
• Authorised defence labs have built NavIC receiver modules for strategic uses.
• Its text channel carries early disaster warnings. These warnings run through the SACHET alert system.

GAGAN stands for GPS Aided Geo Augmented Navigation. The Airports Authority of India and ISRO built it together. It is a satellite-based augmentation system, or SBAS.

How does GAGAN work?

GAGAN does not replace GPS. It takes GPS signals and sends corrections through geostationary satellites. The corrections improve accuracy, integrity and continuity. It is meant for civil aviation.

• ISRO says DGCA certified GAGAN for RNP 0.1 operations on 30 December 2013.
• It was certified for approaches with vertical guidance on 21 April 2015.
• Aircraft registered in India after 1 July 2021 must carry GAGAN equipment.
• In April 2022 an IndiGo flight made a GAGAN-based approach at Kishangarh.

What is the difference in one line?

NavIC is a separate navigation system with its own satellites. GAGAN is a correction layer on top of GPS. The government says NavIC for air traffic management is still under discussion.

Two questions matter most. One is from 2023. The other is from 2018.

Which country has its own satellite navigation system?

UPSC Prelims 2023, Q57 (Series A), asked which of four countries has its own satellite navigation system. The options were Australia, Canada, Israel and Japan. The official answer is (d) Japan. Japan runs QZSS.

What did UPSC ask about IRNSS in 2018?

UPSC Prelims 2018, Q61 (Series A), gave three statements about IRNSS.

• It said IRNSS has three satellites in geostationary and four in geosynchronous orbit. This matches ISRO’s design.
• It said IRNSS covers India and “about 5500 sq. km” beyond its borders. This is wrong. The real figure is a distance of about 1,500 km.
• It said India would have a system with full global coverage by the middle of 2019. This is wrong. NavIC is regional.

So only statement 1 holds. We could not find an official UPSC answer key for this question, so treat this reading as ours.

Where else can GPS be used?

UPSC 2018 Q55 also asked about uses of GPS technology, such as mobile phone operations, banking operations and power grids. Navigation signals give time as well as position, so many services depend on them.