The INSAT Series: India's Multipurpose Satellite Backbone

The Indian National Satellite (INSAT) system is one of the largest domestic communication satellite systems in the Asia-Pacific region. Commissioned with the launch of INSAT-1B in 1983, it is a joint venture of the Department of Space, Department of Telecommunications, India Meteorological Department, All India Radio, and Doordarshan. The INSAT series initiated a major revolution in India’s communications sector and sustained it, while also providing critical services in broadcasting, meteorology, and search and rescue operations.

A defining characteristic of the INSAT system is its multipurpose nature. Unlike many satellite systems that are dedicated to a single function (like communication or earth observation), INSAT satellites often carry a mix of payloads to serve diverse needs simultaneously from their geostationary orbit.

Evolution Through Generations

The INSAT program has evolved through several generations of satellites, each marked by technological advancements and increased capabilities.

INSAT-1 Series (The Beginning): The first-generation INSAT-1 satellites were built by Ford Aerospace in the USA to India's specifications. The series included INSAT-1A, 1B, 1C, and 1D, launched between 1982 and 1990. While INSAT-1A failed early, INSAT-1B was a resounding success and became the foundation of the INSAT system, providing nationwide television coverage and telecommunication links.

INSAT-2 Series (Indigenous Development): The INSAT-2 series marked a significant milestone as these satellites were indigenously designed and built by the Indian Space Research Organisation (ISRO). Launched in the 1990s, this series (2A, 2B, 2C, 2D, 2E) demonstrated India's self-reliance in satellite technology. They offered greater transponder capacity and improved meteorological instruments, such as the Very High Resolution Radiometer (VHRR).

INSAT-3 Series (Enhanced Capabilities): The third generation, launched in the early 2000s, further expanded the system's capacity and capabilities. Satellites like INSAT-3A, 3B, 3C, and 3E provided a mix of communication and meteorological services. This series also included dedicated meteorological satellites like INSAT-3D and INSAT-3DR, which were equipped with advanced atmospheric sounders and imagers.

INSAT-4 Series (Direct-to-Home Focus): The INSAT-4 series, launched from 2005 onwards, was primarily designed to meet the growing demand for high-power Ku-band transponders for Direct-to-Home (DTH) television broadcasting services. Satellites like INSAT-4A and 4B played a key role in the DTH revolution in India.

Below is a representative image of an INSAT series satellite in its geostationary orbit, illustrating its large solar arrays for power generation and multiple antennas for communication and data transmission.

Key Applications and Impact

The INSAT system has had a profound and far-reaching impact on various facets of life in India.

1. Revolutionizing Communications and Broadcasting

• Telecommunications: INSAT satellites provide the backbone for long-distance telephone calls, data transmission, and satellite-based internet services, especially in remote and inaccessible areas like islands and mountainous regions where terrestrial connectivity is difficult.

• Television Broadcasting: The system enabled the rapid expansion of television coverage across India. Doordarshan, the national broadcaster, uses INSAT for its national and regional services. The INSAT-4 series, in particular, fueled the boom in private Direct-to-Home (DTH) satellite TV services, bringing hundreds of channels to millions of households.

2. Meteorology and Disaster Management One of the most critical roles of the INSAT system is in weather forecasting and disaster warning. Satellites like INSAT-3D and INSAT-3DR are dedicated meteorological missions that have significantly improved the accuracy of weather predictions.

• Cyclone Monitoring: INSAT's continuous monitoring helps in tracking cyclones from their formation stage, predicting their path and intensity, and issuing timely warnings. This has been instrumental in saving countless lives during severe weather events like cyclones Phailin, Hudhud, and Fani.

• Weather Instrumentation: These satellites carry sophisticated instruments like a 6-channel Imager and a 19-channel Sounder. The Imager provides images of the earth and clouds in visible and infrared spectral bands, while the Sounder provides vertical profiles of temperature and humidity in the atmosphere.

The following diagram illustrates the complex meteorological payload section of an INSAT-3D series satellite, showing the arrangement of the Imager and Sounder.

3. Search and Rescue INSAT satellites carry a Satellite Aided Search and Rescue (SAS&R) transponder that picks up distress signals from emergency beacons on ships and aircraft. This system is part of the international COSPAS-SARSAT program and has helped save many lives by quickly locating distress sites.

Launching the Satellites

To place these heavy satellites into geostationary orbit, India developed its own powerful launch vehicles. The Geosynchronous Satellite Launch Vehicle (GSLV) is the primary rocket for launching INSAT class satellites. The image below shows a GSLV Mk II on its launchpad at the Satish Dhawan Space Centre in Sriharikota, ready for a mission.

The GSAT Connection

As the communication needs of the country grew exponentially, ISRO started a separate series of satellites called GSAT (Geosynchronous Satellite) to supplement and eventually replace the aging communication satellites in the INSAT fleet. While the "INSAT" name is still used, particularly for meteorological missions, most modern communication satellites launched by India are part of the GSAT series. These GSAT satellites continue the legacy of the INSAT program, providing advanced communication services, including high-throughput broadband.