INSAT, India's Satellite System Since 1983, Carries Television, Telephone Links, Weather Pictures, Cyclone Alerts and Rescue Beacons From Geostationary Orbit

The Indian National Satellite system, INSAT, is a family of satellites parked in geostationary orbit that carries India’s television signals, telephone circuits, weather pictures and distress alerts. ISRO calls it one of the largest domestic communication satellite systems in the Asia-Pacific region. Its page says the system has nine operational communication satellites and more than 200 transponders (the units that pick up a signal and send it back down) in the C, Extended C and Ku radio bands, and that it was established in 1983 with the commissioning of INSAT-1B.

The India Meteorological Department (IMD) describes INSAT as a joint venture of the Department of Space, the Department of Telecommunications, IMD, All India Radio and Doordarshan. Geostationary orbit lies about 36,000 km (22,300 miles) above the equator, the height at which a satellite keeps pace with the Earth’s spin and stays over one spot. ISRO’s pages were checked on 5 November 2026 and carry no date of their own, so the fleet figures are as ISRO states them.

One design, four payloads

Raman Srinivasan’s chapter in NASA’s history of satellite communication says India insisted that INSAT carry at least four different payloads, which shaped its unusual design. He lists television relays for community sets in villages, telephone, fax, data and telegraph links between cities, a remote-sensing package for surveying national resources, and a weather system that gathered readings from several thousand unmanned ground stations and could trigger warning sirens in coastal villages when a cyclone threatened.

The INSAT-1 series that first carried this load was, ISRO’s mission brochure says, custom designed to India’s requirements and made by Ford Aerospace Communication Corporation of the United States. Each spacecraft had 12 C-band transponders for fixed communication, two S-band transponders for television broadcast and a Very High Resolution Radiometer, a scanning camera that takes visible and infrared pictures of the Earth. The ground side was Indian. ISRO says INSAT-1A succeeded in setting up the Master Control Facility at Hassan in Karnataka and the network management system of the Department of Telecommunications.

The experiments that made the case for all this are told in the account of SITE, the 1975 and 1976 satellite television experiment, and the man who started the programme is the subject of the profile of Vikram Sarabhai.

INSAT-1A in 1982, INSAT-1B on the Shuttle’s first night launch

INSAT-1A lifted off on a Delta rocket from Cape Canaveral at 12:17 pm IST on 10 April 1982, and ISRO’s brochure calls it India’s first multipurpose domestic satellite. The timeline lists it as deactivated on 6 September 1982. The brochure says its propellant ran out, gives its life as five months and puts the failure down to a solar sail that did not deploy, together with minor glitches in operations and software. NASA’s press kit for the next mission describes the cause as a failure of the reaction control system, the thrusters that hold a satellite’s attitude.

The replacement, INSAT-1B, went up on Space Shuttle Challenger on 30 August 1983, on the mission called STS-8. NASA’s history of the flight says the placement of INSAT-1B, because of orbital mechanics, dictated that the Shuttle launch at night and land at night, both firsts for the programme. Astronaut Guion Bluford released the satellite on the second day of the flight, and NASA’s press kit says a Payload Assist Module, a solid rocket motor, fired about 45 minutes after release to lift it toward geostationary height, and the satellite’s own motor then rounded off the orbit. On the sixth day Mission Control woke the crew with Ravi Shankar’s “Tala Sawari”, played, NASA says, in honour of the satellite’s release.

The satellite then came close to a repeat of 1982. ISRO says INSAT-1B almost suffered the same fate as INSAT-1A, and Ford and Indian controllers did not get its solar array deployed until mid-September. By then it had been stationed at 74 degrees east in place of INSAT-1A. Full operational capability came in October 1983. The page adds that it kept working into 1990 with all 4,375 two-way voice circuits, or their equivalent, in use, and returned around 36,000 Earth images.

Built in India from 1992

INSAT-2A, in ISRO’s description, was the first multipurpose satellite built by India, and it was operationalised in August 1992. An Ariane 44L carried it up from Kourou in French Guiana on 10 July 1992. The payload was 12 C-band, six extended C-band and two S-band transponders, a data relay transponder for weather data, a transponder for search and rescue, and a radiometer with 2 km resolution in the visible band and 8 km in the infrared. INSAT-2B followed on 23 July 1993, INSAT-2C on 7 December 1995, INSAT-2D on 4 June 1997 and INSAT-2E on 3 April 1999.

Not every satellite came through whole. INSAT-1C, launched in July 1988, lost half its C-band transponders and both S-band transponders to a power failure, ISRO says, while its weather imaging and data collection kept working. The timeline records INSAT-2D becoming inoperable on 4 October 1997 and INSAT-2DT, a replacement, entering the list on 1 January 1998.

INSAT-3A, launched on 10 April 2003, carried 24 transponders (12 C-band, six upper extended C-band and six Ku-band), the radiometer, a camera with 1 km resolution and a search-and-rescue transponder. The list then shows INSAT-4A (22 December 2005), INSAT-4B (12 March 2007) and INSAT-4CR, launched on the Indian GSLV-F04 on 2 September 2007. The same list marks the GSLV-F02 launch of INSAT-4C on 10 July 2006 as unsuccessful.

After INSAT-4CR the INSAT name appears in that list only on the weather satellites INSAT-3D and INSAT-3DR, and most new communication satellites are named GSAT or CMS. INSAT-4B went through disposal at the end of its life and was decommissioned on 24 January 2022.

Weather pictures every 15 minutes

IMD’s account of its satellite division starts before INSAT. From 1972 to 1982 it received images from American weather satellites and printed them on photographic paper to use in forecasting. The data receiving and processing system for INSAT-1B was set up in 1983, and IMD says it turned the work into a full satellite meteorology division. Radiometers on INSAT-1 resolved 2.75 km by 2.75 km in visible light and those on INSAT-2 resolved 2 km by 2 km, and IMD says it acquired scans every three hours. Since 1996 the images have been open to the public on IMD’s website.

Kalpana-1, a dedicated weather satellite, was launched on 12 September 2002. IMD says INSAT-3A was decommissioned in September 2016 and Kalpana-1 in September 2017. IMD’s page, read on 5 November 2026, names INSAT-3D (launched 26 July 2013, at 82 degrees east) and INSAT-3DR (launched 8 September 2016, at 74 degrees east) as the two operational meteorological satellites. Each has a six-channel imager, with 1 km resolution in the visible and shortwave infrared channels, and a 19-channel sounder that builds temperature and humidity profiles of the atmosphere. IMD says it acquires 48 passes a day from each imager, staggered so that a new set of images reaches forecasters every 15 minutes.

IMD lists what the pictures are used for. These include tracking the birth and growth of tropical cyclones, estimating rainfall, and judging the onset of the monsoon, which the science of the monsoon explains. INSAT-3D’s radiances and winds go into the model run by the National Centre for Medium Range Weather Forecasting, and the data relay transponders on both satellites carry readings from automatic weather stations and rain gauges.

INSAT-3DS was launched on GSLV-F14 on 17 February 2024. ISRO’s mission page says it is fully funded by the Ministry of Earth Sciences and will augment the services of INSAT-3D and INSAT-3DR.

A siren on the coast

The cyclone idea in Srinivasan’s list became a service. IMD’s training note on the system says landlines carry its ordinary warnings, and that those are likely to fail in a cyclone, while satellite signals are not affected by bad weather. So in 1985, with the Department of Space, IMD began sending warnings through a C and S band transponder on INSAT. The Cyclone Warning Dissemination System started with 100 analogue receivers along the coast of south Andhra Pradesh and north Tamil Nadu.

Each receiver is a 3.6 m mesh dish with a siren and a loudspeaker. The area at risk is divided into zones, and a coded signal sets off the siren in one zone, after which a voice message follows for the officials who hear it. According to the note, another 150 receivers were installed in the early 1990s along the coasts of Kerala, Karnataka, Maharashtra, Gujarat, Goa, West Bengal, Odisha and north Andhra Pradesh. It adds that 100 digital receivers were put in Andhra Pradesh and one in Kavaratti in Lakshadweep in 2002 and 2003 under World Bank-funded projects, with acknowledgement messages returning to IMD in Chennai through INSAT’s mobile satellite service. At the time of the note, which has no date, IMD counted 252 analogue and 101 digital receivers and planned to move to a system based on direct-to-home set-top boxes. The wider record of warnings is in how India’s cyclone warnings improved.

Distress alerts, television and the transmitters

ISRO’s page for INSAT-3A says its search-and-rescue transponder is part of India’s contribution to the international satellite-aided search programme, and ISRO says INSAT-3DS carries one too. ISRO’s rescue page names INSAT-3DR and GSAT-17 as its space segment in the Cospas-Sarsat system, with the Indian Mission Control Centre at the ISRO Telemetry, Tracking and Command Network in Bengaluru as the nodal agency for distress alerts from India and seven neighbouring countries. That page adds that the Indian ground system has been operational since 1989 to 1990.

On television, ISRO’s page says INSAT has been a major catalyst for the spread of coverage and that Doordarshan is a major user. It reports about 1,415 Doordarshan transmitters working through INSAT, satellite television covering 100 per cent of the area and population, and terrestrial transmitters covering over 81 per cent of the land and over 92 per cent of the population. The page names INSAT-4B among the satellites in use, so it appears to date from before that satellite was decommissioned in January 2022, and it carries no date. ISRO’s frugal space record places these services among its other programmes.

Where the sources differ

ISRO’s own pages disagree in places. Its web page for INSAT-1A says the satellite was abandoned in September 1983, while the mission brochure and the timeline both give 6 September 1982, which is the date used here. ISRO’s timeline dates INSAT-1C to 21 July 1988 and its web page to 22 July 1988, so the article says July 1988. NASA’s press kit gives 8 April 1982 for the INSAT-1A launch, against 10 April in ISRO’s brochure, list and timeline. IMD’s page does not mention INSAT-3DS, launched in February 2024. The fleet totals are ISRO’s undated figures.

The control room at Hassan

ISRO’s INSAT satellites are flown from the Master Control Facility of the Department of Space. The facility at Hassan, with a backup at Bhopal in Madhya Pradesh, monitors and controls all of ISRO’s geostationary satellites, according to its own page, from raising the orbit after launch to testing payloads and moving a satellite out of the way at the end of its life. Its milestones list begins in 1982, when the Hassan centre was set up with two 14 m antennas, and goes on to record the Bhopal backup in 2005, the completion of launch and early-orbit operations for 50 satellites in 2020, and the start of on-orbit operations for 29 spacecraft with the launch of CMS-02 in 2022.