GAGAN: India’s Satellite-Based Augmentation System

UPSC tested GAGAN with three statements in the 2025 Prelims. Two were nearly the words ISRO uses. One was a trap.

What was the question?

This was UPSC Civil Services Prelims 2025, General Studies Paper I, Series A, Question 94. The stem read: “GPS-Aided Geo Augmented Navigation (GAGAN) uses a system of ground stations to provide necessary augmentation. Which of the following statements is/are correct in respect of GAGAN?” The three statements were:

• I. It is designed to provide additional accuracy and integrity.
• II. It will allow more uniform and high quality air traffic management.
• III. It will provide benefits only in aviation but not in other modes of transportation.

The code options were:

• (a) I, II and III
• (b) II and III only
• (c) I only
• (d) I and II only

What is the answer?

The official answer key gives (d) I and II only. The first two statements are correct. The third is wrong.

Why is the third statement wrong?

It uses the word “only”. ISRO says GAGAN benefits go beyond aviation. They reach maritime, road and rail users too.

GAGAN stands for GPS Aided GEO Augmented Navigation. It is India’s own Satellite-Based Augmentation System, or SBAS.

Who built it?

ISRO and the Airports Authority of India built it together.

What does it do?

• It improves the accuracy of GPS with real-time corrections.
• It gives integrity information. This warns a pilot if a GPS signal is unsuitable.
• It allows more uniform, high-quality air traffic management in Indian airspace.

What did the DGCA certify?

India’s civil aviation regulator, the DGCA, certified GAGAN for two services.

• RNP-0.1 navigation over the Indian Flight Information Region.
• APV-1.0 approach with vertical guidance over the Indian landmass.

GPS is good for a car. A plane on final approach needs more.

What goes wrong with GPS?

• GPS signals pass through the ionosphere. This can delay and distort them.
• An SBAS warns the user within a few seconds if the error grows too large.
• Aviation rules ask for more than GPS alone provides in the final approach.

How does an SBAS fix this?

It works in six steps.

• Ground stations receive the GPS signals. Their positions are precisely surveyed, so errors show up.
• The stations send their data to a master centre.
• The master centre works out the corrections and the integrity information.
• Uplink stations send these to a geostationary satellite.
• The satellite rebroadcasts them on a GPS-like signal.
• The aircraft receiver applies the corrections.

GAGAN has a ground part and a space part. Each part has a fixed count.

What is on the ground?

• 15 Indian Reference Stations, called INRES.
• 2 Indian Master Control Centres, called INMCC.
• 3 Indian Land Uplink Stations, called INLUS.
• 4 communication networks.

What is in space?

Three geostationary satellites carry GAGAN payloads. They are GSAT-8, GSAT-10 and GSAT-15. GSAT-8 and GSAT-10 broadcast the signal. GSAT-15 is the in-orbit spare.

What are the key dates?

• 21 May 2011: GSAT-8 launched. It was the first satellite to carry a GAGAN payload.
• 29 September 2012: GSAT-10 launched with a second GAGAN payload.
• 30 December 2013: GAGAN was certified for en-route operation.
• May 2015: GAGAN became fully operational.
• 11 November 2015: GSAT-15 launched, carrying the third payload.
• June 2026: India’s first satellite-based landing system approach on a commercial jet, using GAGAN.

India is not the only country with an SBAS. ISRO says India is the fourth country, after the USA, Europe and Japan, to take up the challenge of establishing a regional SBAS.

Who has an SBAS?

• The United States has WAAS.
• Europe has EGNOS.
• Japan has MSAS.
• India has GAGAN.
• South Korea has KASS, which was commissioned in 2024.

What was special about GAGAN?

ISRO says India is the fourth country to take up the challenge of establishing a regional SBAS. PIB says GAGAN is the first SBAS certified for the equatorial region. Business Today says the ionosphere is difficult to handle over India and changes rapidly.

Can these systems work together?

Yes. GAGAN is interoperable with WAAS, EGNOS and MSAS. They follow the same ICAO standard. A standard receiver gets a similar service from each.

An LPV approach gives a pilot a path sideways and a path downward. It uses satellite signals instead of ground radio aids.

What is APV and LPV?

APV means Approach with Vertical Guidance. LPV means Localizer Performance with Vertical guidance. LPV is one kind of APV approach. By ICAO standards, an APV approach is not a precision approach.

What happened in April 2022?

An IndiGo ATR-72 landed at Kishangarh, Rajasthan, using GAGAN. IndiGo became the first airline in the country to land an aircraft using GAGAN.

What happened in 2026?

PIB says the DGCA conducted India’s first satellite-based landing system approach on a commercial jet in June 2026. News reports say it was an IndiGo Airbus A320 at Udaipur on 27 June.

GAGAN and NavIC solve two different problems.

What is the difference from NavIC?

• GAGAN improves GPS. It serves aviation across the Indian Flight Information Region.
• NavIC is India’s own independent regional navigation system. It covers India and a region up to 1,500 km beyond.
• PIB says India signed a cooperative document in 2025 to set up a NavIC reference station in South Africa.

Is GAGAN only for aviation?

No. This is a common exam trap. GAGAN also helps these areas:

• maritime navigation
• road transport and railways
• disaster management
• defence and security
• telecom timing
• surveying and mapping

UPSC copied ISRO’s wording in this question. Then it reworded the statements.

Which facts should you hold?

• GAGAN is an SBAS. It augments GPS. It is not an independent system like NavIC.
• ISRO and AAI built it together.
• It gives accuracy, integrity and better air traffic management.
• It is not for aviation only.
• Three satellites carry GAGAN payloads: GSAT-8, GSAT-10 and GSAT-15.

What is the common trap?

Look for words such as “only” and “not”. A statement that says GAGAN helps aviation only is wrong. A statement that calls GAGAN an independent system is also wrong.