How ISRO’s InSAT-3DS, to be launched on Saturday, will provide unique weather insights

The GSLV-F14 is all set to launch the InSAT-3DS weather satellite into a geosynchronous transfer orbit (GTO) on February 17 (Saturday) at 5.30 PM from the SDSC-SHAR, Sriharikota. The satellite is expected to undergo a series of manoeuvres to reach its designated geostationary orbit. This will be the GSLV rocket’s 16th mission. The InSAT-3DS satellite will work alongside the currently active InSAT-3D and InSAT-3DR. R stands for ‘repeat’ satellites, significantly expanding India’s meteorological capabilities.

Data from the InSAT-3DS satellite will empower a wide range of agencies within the MoES, including the India Meteorology Department (IMD), National Centre for Medium-Range Weather Forecasting (NCMRWF), Indian Institute of Tropical Meteorology (IITM), National Institute of Ocean Technology (NIOT), Indian National Centre for Ocean Information Services (INCOIS), among others.

Previous satellites in this series include the InSAT-3A, InSAT-3B, and InSAT-3C, all of which are no longer operational. The InSAT-3D is still functioning and will continue to do so until 2024, while the InSAT-3DR is operational and expected to remain so until 2026. The next in line is the InSAT-3DS.

“This mission will utilize advanced instruments to track changes on land and in the oceans, providing crucial data on vegetation health, ocean temperatures and potential hazards. This detailed monitoring will be essential for forecasting weather patterns, understanding climate change and taking environmental protection measures. It has a 6-Channel multispectral imager that acts like a super-powered camera, detecting both visible and invisible light, such as infrared. Its sharp detail and ability to see multiple wavelengths help scientists understand the inner workings of cloud formations, predict rainfall amounts and measure temperatures throughout the atmosphere,” explained space expert Girish Linganna.

In addition to these, it also has a 19-Channel Sounder which is a highly advanced thermometer that checks the temperature of the atmosphere at various heights, from right above the ground to high up in the air. It works by detecting the small amounts of heat energy, known as infrared energy, which the air releases. This tool looks at this energy in 19 different ways—each way focusing on a specific layer of atmosphere. Rather than just giving one overall temperature, the sounder maps out temperatures and moisture at different levels to help weather experts understand the atmosphere’s stability and predict storms.

“It also has a data relay transponder which enhances weather forecasting capabilities by receiving meteorological, hydrological and oceanographic data from automatic data collection platforms or automatic weather stations (AWS). Besides, it has a satellite-aided search and rescue transponder. For instance, if one is lost at sea, or in a remote area and has a special emergency beacon the transponder will listen for distress signals from these beacons. If it hears one, it will quickly alert rescue teams, telling them exactly where to find the person,” remarked Linganna.

The satellite is built using ISRO’s trusted I-2k bus platform and has a starting weight of 2,275 kg when sent into space. When a satellite uses the I-2k bus platform, it usually means that the satellite is of a moderate size and is equipped for various tasks, such as monitoring the Earth, sensing from afar, facilitating communication, and studying the weather.

‘Bus’ refers to a satellite’s fundamental framework and functional base which accommodates and sustains all essential subsystems, including mechanisms for generating and storing power, such as solar panels and batteries; propulsion systems to control the satellite’s position and orbit; communication systems for transmitting and receiving information; thermal control systems to maintain the right temperature; and onboard computers that manage all these functions.

The GSLV on which this satellite will be launched is a flexible launch vehicle, deploying satellites for communications, navigation, Earth resource surveys and other missions. While traversing Earth’s atmosphere, the valuable payload is safeguarded from atmospheric forces by Ogive payload fairing, a nose-cone-like structure providing critical protection to the satellite.

The 51.7-metre GSLV, weighing 420 tons, uses a three-stage design. The GS1 first stage is built around an S139 solid-propellant motor (139 tons) and augmented by four L40 liquid-propellant strap-ons (40 tons each). Stage two (GS2) relies on an Earth-storable liquid-propellant engine (40 tons). The final stage (GS3) is cryogenic, fuelled by 15 tons of liquid oxygen and liquid hydrogen.

Explaining about the GTO, the space expert said it is a highly elliptical, temporary path used to launch satellites. “Picture it as a stretched-out oval around Earth, with its closest point (perigee) usually a few hundred kilometres above the surface and farthest point (apogee) around 36,000 kilometres out. Later, the satellite uses its own engines to move into a geosynchronous orbit. This is a special circular orbit about 36,000 kilometres above the Earth,” said Linganna.

But how does the INSAT-3DS compare with other global weather satellites? “The Meteosat (Europe): Europe’s Meteosat satellites, operated by EUMESTAT, provide similar and, in some ways, more advanced capabilities than ISRO’s INSAT-3DS. They offer higher spatial resolution and capture images more frequently for detailed European weather observations. Similarly, Geostationary Operational Environmental Satellites (GOES) from the United States (NASA builds and launches the GOES and NOAA operates them) are some of the most advanced weather satellites currently in operation. Their capabilities exceed those of the INSAT-3DS, providing wider spectral coverage and finer details for critical meteorological information across the Americas. Also, the Japan Meteorological Agency’s Himawari satellites excel in very high-frequency image updates crucial for real-time monitoring of severe weather patterns and phenomena within East Asia and the Western Pacific,” remarked Linganna.

But space experts point out that each satellite system (India, Europe, US, Japan) primarily supports the meteorological needs of its respective region. This regional specialization means the satellites are configured to collect data tailored to the particular weather patterns and conditions of their areas.

There’s a continual evolution in satellite technology. Newer generations of weather satellites (like GOES-16 and beyond) possess even greater spectral bands, more sensitive instruments, and faster data capturing than their predecessors, including the INSAT-3DS. Satellites might differ in their emphasis: some excel in severe storm monitoring, others in climate data collection, and others in atmospheric composition analysis.