Maarg Manthan · Topic 12.4

Satellite Systems: INSAT, GSAT, IRS (Remote Sensing)

Science & Technology › Space Technology and ISRO · Topic 12.4

India operates three main families of satellites. The Indian National Satellite System, INSAT, started in 1983 and is one of the largest domestic communication satellite systems in the Asia-Pacific region, serving telecommunication, television, radio, weather and disaster warning. GSAT satellites are communication satellites launched from the mid 2000s that carry newer transponders and are placed in geostationary orbit. The Indian Remote Sensing, IRS, satellites began with IRS-1A in 1988 and observe the Earth from sun-synchronous orbit for agriculture, forests, water, cities and disasters. Later Earth observation satellites are also named Cartosat, Resourcesat, Oceansat, RISAT and EOS.

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

At a Glance

INSAT Multipurpose, from 1983
GSAT Communication, geostationary
IRS Remote sensing, from 1988
Orbit of IRS Sun-synchronous
Orbit of INSAT and GSAT Geostationary
Exam link UPSC Prelims, Science & Technology: Space Technology and ISRO

Where Does It Fit?

This topic follows the account of ISRO. It lists the satellites that ISRO builds to serve the country, which fall into communication and Earth observation groups. Previous topic: ISRO’s Space Research Programme and ANTRIX Corporation. Next topic: Launch Vehicle Technology: PSLV, GSLV and Cryogenic Engines.

What Are the Three Families and Their Uses?

Family	Features
INSAT	Multipurpose system launched from 1983, with INSAT-1B as the first fully working satellite. Provides telecommunications, TV broadcast, meteorology, search and rescue and disaster warning. In geostationary orbit
GSAT	Series of communication satellites developed by ISRO from 2001, for example GSAT-11 weighing about 5.8 tonnes, launched in 2018, and GSAT-7 for the Navy. Carry C, extended C, Ku and Ka band transponders
IRS	Remote sensing satellites from IRS-1A in 1988, in sun-synchronous orbit around 500 to 900 km. Resourcesat, Cartosat, Oceansat, RISAT, Megha-Tropiques and others
Weather satellites	INSAT-3D, 3DR and 3DS provide imaging and sounding for weather forecasts
Military communication	GSAT-7 series serve the Navy, Air Force and Army
Navigation	NavIC and GAGAN are in separate navigation series, as in Navigation Satellite Systems: GPS, Galileo, GLONASS, NavIC (IRNSS), GAGAN
Earth Observation Satellites	ISRO has begun naming newer Earth observation satellites as EOS series

Which Remote Sensing Satellites Matter?

Cartosat: high-resolution optical imaging for mapping and urban planning. Cartosat-3 launched in 2019 has a resolution of about 0.25 metres
Resourcesat: multispectral sensors LISS-III, LISS-IV and AWiFS for crops, forests and water
Oceansat: ocean colour and wind measurement for fisheries and ocean studies
RISAT: radar imaging satellites with synthetic aperture radar that see through cloud and at night
Megha-Tropiques: a satellite with France for the water cycle and climate in the tropics, launched in 2011
SARAL: satellite with ARGOS and AltiKa, a joint mission with France for ocean altimetry
HySIS: hyperspectral imaging satellite launched in 2018, as in Hyperspectral Imaging Satellite and Water Propulsion System in CubeSats
EOS-04 and EOS-08: recent satellites for radar imaging and for disaster monitoring and environment

What Else Should You Remember?

Transponder: the part of a communication satellite that receives a signal, amplifies it and sends it back at another frequency
Frequency bands: C band suits wide coverage and is less affected by rain, Ku and Ka bands give higher capacity with smaller dishes but are more affected by rain
Number of transponders: INSAT and GSAT together make India’s communication system among the largest in the region
Applications of INSAT: television, direct to home, telemedicine, tele-education and village resource centres
Applications of IRS: crop area and yield estimates, forest cover mapping, groundwater prospects, flood and drought assessment, urban sprawl
Bhuvan: ISRO’s geoportal that offers satellite maps and data to the public
Disaster support: data from INSAT and IRS are used for cyclone warning, flood mapping and forest fire alerts
Heaviest GSAT: GSAT-11 weighed 5,854 kg and was launched by Ariane 5 in 2018. India has launched heavy satellites abroad because its own launch vehicles were smaller
GSAT-N2: a high throughput Ka band satellite launched on a commercial rocket in January 2025, mainly for broadband and in-flight connectivity
Life of satellites: a geostationary communication satellite typically works for 12 to 15 years
New Space India: NSIL has taken up demand driven satellites, for example GSAT-24 for DTH, as in ISRO’s Space Research Programme and ANTRIX Corporation
Link: more detail on applications is in Earth Observation Systems and INSAT/GSAT/IRS Applications in Detail
Disaster Management Support: ISRO gives satellite based warnings and maps to the National Disaster Management Authority during cyclones and floods
Gap years: some Earth observation satellites have retired, so continuous replacement is needed to keep data without breaks
Naming habit: INSAT-3D and INSAT-3DR carry imagers and sounders, while Kalpana-1 was an early dedicated meteorological satellite in the INSAT system

Why Does It Matter for the Exam?

Families: INSAT, GSAT and IRS
Orbits: GEO for communication, SSO for IRS
Satellite names: Cartosat, Resourcesat, Oceansat, RISAT
Current affairs link: new EOS and communication satellites
Common errors: placing IRS satellites in geostationary orbit

As an analytical point, India’s satellite fleet supports daily life from television to crop estimates. Moving to high throughput and private operated satellites will raise capacity and bring broadband to remote areas.

Why Is This Topic Important?

Families Three groups
Orbits GEO versus SSO
Uses Weather to farms

What Came Next?

The next topic covers launch vehicle technology of PSLV, GSLV and cryogenic engines. Next topic: Launch Vehicle Technology: PSLV, GSLV and Cryogenic Engines.

Key People and Terms

Transponder Relay unit on a satellite
C band Radio band 4 to 8 GHz
LISS Linear imaging self scanning sensor
SAR Radar that images through clouds
Resolution Smallest detail seen
DTH Direct to home TV

Exam Corner

Points to Remember

INSAT began in 1983.
IRS-1A: 1988.
Cartosat-3: about 0.25 m resolution.
IRS orbit: sun-synchronous.
GSAT-11: about 5.8 tonnes.

Do Not Confuse With

INSAT and IRS Communication and weather versus remote sensing
Cartosat and RISAT Optical versus radar
GSAT and NavIC Communication versus navigation

Memory Hook

INSAT in the high for calls and weather, IRS in the low for the land and sea.

Mains Angle

Questions ask to match series with use and orbit. These points help.

Services Communication and weather
Observation Resources and disasters
Trend High throughput

A Question You May Face

An original practice question, not a past paper question.

“Discuss the contribution of INSAT, GSAT and IRS satellite systems to India’s development.”

How to Answer

Families Three groups.
Uses TV to crops.
Disasters Warning and mapping.
Way Capacity and private role.

GS Relevance

Prelims: three satellite families, orbits, applications, example satellites. GS Paper 3: science and technology, space applications.

Frequently Asked Questions

What is INSAT?

INSAT, the Indian National Satellite System, is a series of multipurpose geostationary satellites started in 1983 that provides telecommunication, television broadcasting, weather observation and disaster warning. It is one of the largest domestic satellite systems in the Asia-Pacific region and is run by ISRO with the Department of Space.

What is the difference between INSAT and IRS?

INSAT satellites are in geostationary orbit about 36,000 kilometres high and give communication and weather services over India. IRS satellites are in sun-synchronous orbit at 500 to 900 kilometres and carry sensors for imaging the Earth's surface, used for agriculture, forests, water resources and urban planning.

What is a transponder?

A transponder is the part of a communication satellite that receives a signal from the ground, amplifies it, changes its frequency and sends it back to Earth. A satellite has many transponders working in bands such as C, Ku and Ka. The number and capacity of transponders decide how much traffic a satellite can handle.

What is the Cartosat series used for?

Cartosat satellites carry high-resolution panchromatic cameras for mapping, urban and rural planning, land use and infrastructure monitoring. Cartosat-3, launched in November 2019, has a resolution of about 0.25 metres, one of the sharpest of any civil satellite in the world at that time.

What is RISAT?

RISAT, or Radar Imaging Satellite, is a series of Indian satellites that carry synthetic aperture radar. Radar can see through clouds and in darkness, so RISAT images help in monsoon flood mapping, crop monitoring, disaster response and also in surveillance, which optical satellites cannot do in poor weather.

PYQ Practice — Statement Analysis

1 IRS satellites are placed in sun-synchronous orbit.

True

For consistent lighting.

2 INSAT was started in 1983.

True

INSAT-1B was the first fully working satellite.

3 RISAT satellites carry optical cameras only.

False

They carry radar.

4 GSAT satellites are remote sensing satellites.