By Girish Linganna

Feb, 16: The Indian Space Research Organisation (ISRO) is gearing up for the significant launch of a sophisticated weather satellite—the InSAT-3D Second Repeat (InSAT-3DS)—using the GSLV-F14 rocket, scheduled at 5:35 pm on Saturday (February 17, 2024) according to an ISRO tweet on February 15. The InSAT-3DS is set to join forces with the operational InSAT-3D and InSAT-3DR satellites, where ‘R’ signifies the ‘repeat’ satellites, thereby greatly enhancing India’s weather observation capabilities. 

Building on the progress of third-generation weather satellites in geostationary orbit, the InSAT-3DS—the seventh satellite in the InSAT-3 series—was planned as part of the GSLV-F14 mission. This satellite’s development, entirely financed by the Ministry of Earth Sciences (MoES), is aimed at enhancing weather observations and providing detailed information about terrestrial and marine environments to improve weather prediction and disaster management efforts. 

This mission will employ sophisticated tools to observe alterations to Earth’s surface and in the oceans, delivering vital information about the health of vegetation, sea temperatures and potential risks. Such comprehensive surveillance is key to predicting weather trends, grasping the nuances of climate change and implementing actions for environmental conservation.

This addition to India’s satellite fleet will bolster the capabilities of several MoES agencies, such as 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) and the Indian National Centre for Ocean Information Services (INCOIS), supporting a broad spectrum of meteorological and oceanographic research and services. 

The InSAT-3DS has a launch weight of 2,275 kg and is equipped with advanced payloads to enhance weather monitoring. It utilizes ISRO’s dependable I-2K (2000) bus platform. A satellite bus platform is like the main body, or chassis, of a satellite. It provides a standard, modular base that holds all the crucial systems needed for the satellite to work. It is where all the main parts that keep the satellite running are attached. The payload, which changes based on what the satellite is meant to do, is then added onto this bus. 

The I-2K satellite bus built by ISRO is designed for satellites that weigh around 2,000 kg. The ‘I’ in I-2K refers to InSAT—a series of communication satellites ISRO has developed and launched. ISRO created this satellite bus to work well with smaller and medium-sized satellites. The I-2K bus can provide up to 3,000 watts of DC power. It is meant for satellites that weigh between 1,500 kg and 2,500 kg when they launch.

The satellite comes with four sophisticated tools, or payloads. These include:

1. A six-channel imager, and 

2. A 19-channel sounder for detailed observations; 

3. A Data Relay Transponder (DRT) for transmitting data, and 

4. A transponder designed for Satellite-Aided Search and Rescue (SAS&R) missions 

These instruments are specially made for studying and monitoring Earth’s land and ocean areas and will collect important information for improving the accuracy of weather predictions and providing early alerts for natural disasters. This will boost India’s readiness and ability to respond to such events. 

The 4 Payloads on InSAT-3DS 

1. The 6-channel multispectral imaging system acts like a high-tech camera that takes pictures of Earth using 6 different types of light beyond what our eyes can see. This advanced technology allows scientists to observe Earth in unique ways, revealing hidden details about vegetation health, water quality and various surface materials. By analysing these images, researchers can better understand environmental changes and monitor crop conditions—and even detect pollution in air and water, providing valuable insights that are not visible in regular photographs. 

2. The 19-channel sounder device acts as an extremely sophisticated thermometer that measures atmospheric temperature at different altitudes—from that on Earth’s surface to the upper atmospheric layers. It operates by sensing tiny quantities of heat, or infrared energy, emitted by the atmosphere. The device examines this energy through 19 distinct channels, with each channel targeting a specific atmospheric layer. Instead of providing a single temperature reading, the sounder creates a detailed profile of temperature and humidity across various layers, helping meteorologists assess atmospheric conditions and forecast storms. 

3. The Data Relay Transponder is a device that boosts the ability to forecast weather by collecting meteorological, hydrological and oceanographic information from automated data-gathering platforms or automated weather stations (AWS). This instrument plays a crucial role in improving weather predictions by seamlessly transmitting valuable data from these stations—strategically placed in various locations—to analysts. This ensures that the latest and most accurate environmental data is available for forecasting and monitoring purposes, enhancing our understanding of weather patterns, water cycles and ocean behaviours. 

4. The Satellite-Aided Search & Rescue (SAS&R) Transponder functions as an advanced radio receiver on a satellite, specifically designed to detect emergency signals from beacons carried by individuals in distress, whether they are at sea, or in isolated locations on land. When this system picks up a distress signal, it swiftly notifies the appropriate rescue authorities, providing them with precise locational information to facilitate rapid response. This technology is a critical tool for enhancing the effectiveness and efficiency of search-and-rescue operations, ensuring that help can be dispatched promptly to those in urgent need, regardless of their location. 

The GSLV-F14 Launch Vehicle 

The GSLV is a versatile launch vehicle, or rocket, used for placing satellites into orbit for a variety of purposes—including communications, navigation and Earth observation. As it moves through Earth’s atmosphere, the satellite is protected from atmospheric pressures by an Ogive-shaped payload fairing, which acts like a protective nose cone.

The 51.7-metre-tall, 420-ton GSLV features a three-stage design: 

o The first stage, GS1, centers on an S139 solid-propellant motor that holds 139 tons of fuel and is enhanced by four L40 liquid-propellant boosters, each carrying 40 tons of fuel 

o The second stage, GS2, operates with a 40-ton earth-storable liquid-propellant engine 

o The third and final stage, GS3, uses a cryogenic engine running on 15 tons of liquid oxygen and hydrogen, marking the advanced phase of the launch that propels the satellite into its designated orbit 

(The author Girish Linganna of this article is a Defence, Aerospace & Political Analyst based in Bengaluru. He is also Director of ADD Engineering Components, India, Pvt. Ltd, a subsidiary of ADD Engineering GmbH, Germany. You can reach out to him at: girishlinganna@gmail.com)