Science & Technology
Space and Defence Technology
Satellites and Their Applications: Communication, Earth Observation and NavIC
INSAT/GSAT, IRS and EOS, NISAR, NavIC and GAGAN, and how space data serves farming, disasters and governance in Chhattisgarh — status as of 2026.
Prerequisites
- Indian Space Programme: Evolution, Institutions and Launch Vehicles — orbits (GEO, SSO) and which rocket carries what.
- Light and Sound — the electromagnetic spectrum explains optical versus radar imaging.
The Hook: Counting Paddy From Space
Connect
Chhattisgarh is called the “rice bowl” (धान का कटोरा) of central India. Every kharif season someone has to estimate how many hectares are under paddy — for procurement planning, crop insurance and drought relief. Walking every field is impossible.
For about two decades, scientists of the Chhattisgarh Council of Science and Technology (CCOST) have worked with the national Mahalanobis National Crop Forecast Centre (MNCFC) to estimate rice acreage using satellite images. Radar satellites can “see” paddy fields even under monsoon clouds.
Which satellites make this possible, and what else do they do? That is this page — the “application” half of Sarabhai’s vision.
Why it matters: Prelims asks you to match satellites with purposes (NavIC, GAGAN, RISAT, INSAT-3DS). Mains GS-II asks “role of space technology in national development / disaster management / agriculture” — this page gives you the examples.
Types of Satellites (उपग्रह)
| Type | Orbit | Indian series | What it does |
|---|---|---|---|
| Communication | GEO | INSAT, GSAT, CMS | TV broadcasting (DTH), telephony, internet, VSAT banking, tele-education and tele-medicine |
| Meteorological | GEO | INSAT-3D, 3DR, 3DS (launched Feb 2024) | Cloud imagery, temperature and humidity profiles, cyclone tracking for IMD |
| Earth observation / remote sensing | Sun-synchronous polar | IRS, Resourcesat, Cartosat, Oceansat, RISAT, EOS series | Maps, crops, forests, water, urban planning, defence |
| Navigation | GEO + inclined GSO | NavIC (IRNSS / NVS) | Position, navigation and timing over India |
| Scientific | Various | AstroSat, Aditya-L1, XPoSat | Astronomy and solar physics (see Space Exploration) |
| Strategic | GEO / LEO | GSAT-7 (“Rukmini”, Navy, 2013), GSAT-7A (Air Force, 2018), RISAT, EMISAT | Secure military communication and surveillance |
Optical vs radar imaging
- Optical satellites (Cartosat, Resourcesat) record reflected sunlight. They give sharp, colour images but cannot see through clouds or at night.
- Synthetic Aperture Radar (SAR) satellites (RISAT, EOS-04, NISAR) send their own microwave pulses and record the echo. They work day and night and through clouds — vital in a monsoon country.
So a question like “which satellite can monitor floods during heavy cloud cover?” always points to a radar (SAR) satellite.
Communication Satellites: The INSAT System
- INSAT (Indian National Satellite System), started in 1982–83, is one of the largest domestic communication satellite systems in the Asia-Pacific region. It combined communication, broadcasting and meteorology in the same satellites — a cost-saving Indian design.
- Today the communication fleet is mostly GSAT satellites. Some heavy ones were launched abroad when India lacked a big enough rocket. For example, GSAT-20 (GSAT-N2), a high-throughput Ka-band satellite built for NSIL, was launched on a SpaceX Falcon 9 in November 2024.
- NSIL’s “demand-driven” model (since 2022): NSIL owns and funds satellites based on confirmed customer demand (for example DTH operators), instead of ISRO building them first.
Uses you can quote: DTH television in remote villages, VSAT connectivity for bank branches and ATMs, tele-medicine links to district hospitals, SWAYAM Prabha / PM e-Vidya DTH education channels, emergency communication when ground networks fail.
Earth Observation (पृथ्वी अवलोकन)
| Satellite / series | Special feature |
|---|---|
| IRS-1A (1988) | First Indian remote-sensing satellite |
| Cartosat series | High-resolution optical imagery for mapping and urban planning |
| Resourcesat | Agriculture, land use, water resources |
| Oceansat | Ocean colour, winds — potential fishing zone advisories via INCOIS |
| RISAT / EOS-04 | Radar imaging in all weather |
| NISAR (2025) | NASA–ISRO radar satellite (below) |
NISAR — the flagship joint mission
| Point | Detail |
|---|---|
| Full name | NASA–ISRO Synthetic Aperture Radar |
| Launch | 30 July 2025, on GSLV-F16 from Sriharikota, into a sun-synchronous orbit (~740 km) |
| Radars | Dual-frequency: L-band (NASA/JPL) and S-band (ISRO’s SAC) — the first satellite to fly both |
| Antenna | A ~12 m deployable mesh reflector |
| Coverage | Images nearly all of Earth’s land and ice surfaces every 12 days |
| Uses | Earthquakes and land subsidence, glaciers and ice sheets, forest biomass, soil moisture, crop monitoring, floods and landslides |
| Status (as of 2026) | Commissioning completed in late 2025; the mission moved into science operations around the turn of 2025–26 and is producing data |
Why NISAR matters for Mains
NISAR is the clearest example of India–US space partnership as equals: each agency built one radar and shared costs, and the data is to be freely available. It also shows a shift in GSLV’s role — the first GSLV launch into a sun-synchronous orbit.
Navigation: NavIC and GAGAN
NavIC (Navigation with Indian Constellation, नाविक)
| Point | Detail |
|---|---|
| Original name | IRNSS (Indian Regional Navigation Satellite System) |
| Design | 7 satellites: 3 in geostationary orbit + 4 in inclined geosynchronous orbit |
| Coverage | India and about 1,500 km around it |
| Services | Standard Positioning Service (civilian) and Restricted Service (encrypted, strategic users) |
| Why India built it | Not to depend on the US GPS in a crisis. The often-cited trigger is the Kargil war (1999), when India could not get the GPS data it wanted. |
| Second generation | NVS series with an indigenous rubidium atomic clock and the L1 band (compatible with ordinary smartphone chips). NVS-01 launched May 2023 |
| Problem | Several first-generation satellites lost their atomic clocks; NVS-02 (Jan 2025) could not reach its final orbit after a valve failure |
| Status (as of early Oct 2026) | Fewer than the four working satellites needed for standalone positioning; NVS-03 was being readied on a GSLV for a launch targeted in October 2026, which would restore four working satellites |
Regional vs global
NavIC is regional, like Japan’s QZSS. Global systems are GPS (USA), GLONASS (Russia), Galileo (EU) and BeiDou (China). A favourite statement trap: “NavIC provides global coverage” — false.
GAGAN (GPS Aided GEO Augmented Navigation)
- A Satellite-Based Augmentation System (SBAS) built by ISRO and the Airports Authority of India (AAI).
- It corrects GPS signals using ground reference stations and GEO satellites, so aircraft can make precise approaches and save fuel.
- It does not provide independent positioning — it improves GPS. India became one of the few countries with a certified SBAS (after the US WAAS, Europe’s EGNOS and Japan’s MSAS).
Applications: From Village to Nation
| Sector | How space helps | Example |
|---|---|---|
| Agriculture | Crop acreage and yield forecasts, drought assessment, crop insurance | FASAL (crop forecasting, run with MNCFC); satellite data in PM Fasal Bima Yojana assessments; CCOST rice-acreage work in Chhattisgarh |
| Weather and disasters | Cyclone tracking, flood mapping, early warning | INSAT-3D/3DR/3DS for IMD; ISRO’s Decision Support Centre at NRSC maps floods and fires |
| Forests | Forest cover mapping, fire alerts | Forest Survey of India’s biennial State of Forest Report uses IRS imagery — key for a forest-rich state like Chhattisgarh |
| Water | Watershed and groundwater prospect maps | Planning check dams and tanks |
| Fisheries | Potential Fishing Zone (PFZ) advisories | INCOIS, Hyderabad, using ocean satellites |
| Governance | Geo-tagging of assets, land records | Bhuvan geoportal (NRSC); geo-tagged MGNREGA assets; Bhuvan Panchayat |
| Health and education | Tele-medicine and tele-education | SITE (1975–76) was the pioneer; DTH education channels today |
| Security | Border and coastal surveillance, secure communication | GSAT-7/7A; radar imaging satellites |
Chhattisgarh angle
- CCOST, Raipur applies remote sensing to agriculture, forests and water resources, including long-running rice acreage estimation with MNCFC.
- Chhattisgarh signed an agreement with ISRO (reported in early 2025) to use space technology in governance, agriculture, environmental management and disaster preparedness.
- With large forest areas, mineral belts (Korba, Dantewada, Raigarh) and tribal regions with weak roads, satellite mapping, NavIC/GPS and satellite communication are practical tools for mine monitoring, forest-fire alerts and connectivity in remote Bastar villages.
Use one or two of these lines to localise a Mains answer.
Memory Tricks
NavIC = '3 + 4 = 7, 1500 around'
3 geostationary + 4 inclined geosynchronous = 7 satellites, covering India plus about 1,500 km.
'GAGAN corrects, NavIC computes'
GAGAN only improves GPS for aircraft. NavIC is an independent navigation system.
NISAR = 'L for the Larger partner, S for Swadeshi'
L-band radar from NASA (JPL), S-band radar from ISRO (SAC); launched from Sriharikota on GSLV-F16, 30 July 2025.
Don’t Confuse
| This | vs | That |
|---|---|---|
| NavIC — independent regional navigation (ISRO) | vs | GAGAN — GPS augmentation for aviation (ISRO + AAI) |
| INSAT-3DS — weather, geostationary | vs | Oceansat — ocean observation, polar orbit |
| Optical (Cartosat) — no cloud penetration | vs | SAR (RISAT, NISAR) — all-weather, day-night |
| Bhuvan — ISRO’s geoportal (NRSC) | vs | Bhuvan Panchayat / Bhuvan apps — sector-specific portals built on it |
| FASAL — crop production forecasts | vs | PFZ — fishing zone advisories (INCOIS) |
Common Mistakes
MCQ traps
- “NavIC covers the whole world.” False. It is regional (India + ~1,500 km).
- “NISAR was launched by a NASA rocket.” False. It was launched by ISRO’s GSLV-F16 from Sriharikota.
- “GAGAN is India’s alternative to GPS.” False. It augments GPS; NavIC is the alternative.
- “Remote-sensing satellites are placed in geostationary orbit.” Mostly false. Earth-observation satellites use sun-synchronous polar orbits; GEO is for communication and weather.
- “NavIC is fully operational with seven satellites (2026).” False. Clock failures and the NVS-02 problem left it short of four working satellites; NVS-03 was due in October 2026.
Practice
All questions below are original practice questions written in CGPSC style. They are not previous-year questions.
Level 1: Foundation
- NavIC was earlier known as ______.
- Radar imaging satellites can see through clouds because they use ______ waves.
- NISAR carries radars in the L-band and the ______-band.
Answers
- IRNSS (Indian Regional Navigation Satellite System).
- Microwave (radio) waves — they penetrate clouds and work at night.
- S-band (built by ISRO).
Level 2: Prelims MCQs
Q1. Consider the following statements about NavIC:
- It is designed with seven satellites in geostationary and geosynchronous orbits.
- Its coverage extends about 1,500 km beyond India’s boundary.
- Its second-generation satellites support the L1 frequency band.
Which of the statements given above is/are correct?
- (a) 1 and 2 only
- (b) 2 and 3 only
- (c) 1 and 3 only
- (d) 1, 2 and 3
Answer and explanation
(d) 1, 2 and 3. NavIC is designed as 3 GEO + 4 GSO satellites covering India plus about 1,500 km. The second-generation NVS satellites add the L1 band, which ordinary consumer devices use, and carry indigenous rubidium clocks.
Q2. Match List I (Satellite / system) with List II (Primary purpose):
| List I | List II |
|---|---|
| A. INSAT-3DS | 1. Aviation-grade correction of GPS signals |
| B. GAGAN | 2. All-weather radar imaging of Earth |
| C. RISAT | 3. Meteorology |
| D. GSAT-7 | 4. Naval communication |
- (a) A-3, B-1, C-2, D-4
- (b) A-3, B-2, C-1, D-4
- (c) A-4, B-1, C-2, D-3
- (d) A-1, B-3, C-2, D-4
Answer and explanation
(a) A-3, B-1, C-2, D-4. INSAT-3DS (Feb 2024) is a weather satellite; GAGAN is the ISRO–AAI SBAS for aviation; RISAT is the radar imaging series; GSAT-7 (“Rukmini”, 2013) serves the Indian Navy.
Q3. Which of the following is the most suitable for mapping flood-affected areas in Chhattisgarh during continuous monsoon cloud cover?
- (a) An optical Cartosat image
- (b) A synthetic aperture radar image
- (c) An INSAT visible-band image
- (d) A thermal infrared image from a geostationary satellite
Answer and explanation
(b). SAR sends its own microwave pulses that pass through clouds and work at night. Optical and visible-band images are blocked by cloud, and geostationary infrared images are far too coarse for field-level flood maps.
Q4. With reference to NISAR, which one of the following statements is not correct?
- (a) It is a joint mission of NASA and ISRO.
- (b) It was launched by ISRO’s GSLV in July 2025.
- (c) It carries only an L-band radar built by ISRO.
- (d) It images nearly all land and ice surfaces every 12 days.
Answer and explanation
(c) is not correct. NISAR is dual-frequency: the L-band radar came from NASA (JPL) and the S-band radar from ISRO (SAC). The other three statements are correct.
Level 3: Mains Answer Writing
Q1. (150–200 words) “Space technology is a tool of development, not a luxury.” Discuss with examples, including from Chhattisgarh.
Model answer outline
- Intro: Sarabhai’s application-first vision; India’s space budget is small relative to the services it supports.
- Body:
- Agriculture: crop acreage and yield forecasts (FASAL), drought assessment, crop-insurance support; CCOST–MNCFC rice estimates in Chhattisgarh.
- Disasters: INSAT-3D/3DS cyclone tracking; radar flood maps (RISAT, NISAR); NRSC Decision Support Centre.
- Forests and environment: FSI forest cover maps; fire alerts in forest-rich states like Chhattisgarh.
- Connectivity and inclusion: DTH, VSAT banking, tele-medicine and tele-education to remote Bastar villages.
- Governance and security: Bhuvan geo-tagging, NavIC timing for power grids and banking; GSAT-7/7A for the forces.
- Balance: delays in NavIC replenishment and launch failures show the need for redundancy and private participation.
- Conclusion: Every rupee in space returns as services on the ground — a development tool, not a luxury.
Q2. (100 words) Why did India develop NavIC when GPS is freely available?
Model answer outline
- Strategic autonomy: GPS is controlled by a foreign military and can be degraded or denied in a crisis (the Kargil experience is often cited).
- Restricted Service for armed forces; precise timing for banking, power grids and telecom.
- Better accuracy over India from satellites that stay over the region.
- Challenge: clock failures and replenishment delays; NVS series (L1 band, indigenous clocks) is the fix.
- Conclusion: NavIC is a sovereign utility, like having our own power grid.
Quick Revision Table
| Fact | Detail |
|---|---|
| INSAT started | 1982–83; combined communication + weather |
| Weather satellites | INSAT-3D, 3DR, 3DS (Feb 2024) |
| First IRS | IRS-1A, 1988 |
| GSAT-7 / 7A | Navy “Rukmini” (2013) / Air Force (2018) |
| NISAR | NASA–ISRO; L + S band SAR; GSLV-F16, 30 Jul 2025; 12-day global coverage |
| NavIC | 7 satellites (3 GEO + 4 GSO); India + ~1,500 km; SPS and RS |
| NVS-01 | May 2023; indigenous rubidium clock; L1 band |
| NVS-02 | Jan 2025; stuck short of final orbit |
| NVS-03 | Launch targeted Oct 2026 (as of early Oct 2026) |
| GAGAN | ISRO + AAI; SBAS augmenting GPS for aviation |
| Bhuvan | ISRO geoportal by NRSC, Hyderabad |
| PFZ advisories | INCOIS, Hyderabad |
| CG angle | CCOST rice acreage with MNCFC; state–ISRO agreement (2025) |
Key Takeaways
Key Takeaways
- Orbit follows purpose: GEO for communication and weather; sun-synchronous polar for Earth observation.
- Radar (SAR) works through cloud and at night — NISAR (2025) is the flagship, built jointly with NASA.
- NavIC is regional and independent; GAGAN only augments GPS. NavIC needs replenishment (NVS-03 due Oct 2026).
- Applications in agriculture, disasters, forests, fisheries and governance are the core of any Mains answer.
- Chhattisgarh uses space data for rice acreage, forest cover and governance — quote it for local flavour.
What’s Next
- Space Exploration and Human Spaceflight — the science missions
- Computers and Information Technology — data, networks and digital governance that use satellite links
- Agriculture and Irrigation in Chhattisgarh — where crop-monitoring data is applied
- Forests, Wildlife, National Parks and Sanctuaries — forest cover figures that come from satellite mapping
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