ISRO is preparing for a high-stakes launch in the early hours of September 4, with the GSLV-F17 mission set to put an advanced Earth observation satellite into space.
The rocket is scheduled to lift off from the Second Launch Pad at Sriharikota at 2.55 am, carrying EOS-5. Once deployed, the satellite will operate from geosynchronous orbit at an altitude of nearly 36,000 kilometres, giving it a continuous view of India and the surrounding region.
The timing of the mission is significant. ISRO is coming off a difficult period in which its PSLV launcher suffered successive failures in 2025 and 2026. The setbacks have led to the PSLV being grounded while investigations and further tests are carried out.
GSLV-F17, however, is not part of the PSLV programme. The two rockets use different propulsion systems and engines, meaning the problems associated with the PSLV do not directly affect the GSLV Mk II. The upcoming flight will therefore provide an independent test of the GSLV’s performance.
A Rocket With a Reputation
The GSLV Mk II has itself experienced a turbulent journey. The launcher has long been referred to inside ISRO as the “naughty boy”, a nickname linked to its unpredictable performance during its early years. Of its first 18 missions, six failed to achieve complete mission success.
Much of the rocket’s significance comes from its cryogenic upper stage. Developing that technology was a major challenge for India’s space programme.
India had sought access to cryogenic technology from Russia during the 1990s. The proposed arrangement came under opposition from the United States, which raised concerns over the possible transfer of technology with missile applications. International restrictions eventually prevented India from obtaining the technology as originally intended.
ISRO then began developing its own cryogenic propulsion system. The process took years of research, testing and failures. Cryogenic engines require the handling of liquid hydrogen and liquid oxygen at temperatures below minus 250 degrees Celsius, making them among the most demanding propulsion systems to develop.
India’s eventual success in building the technology gave the country greater independence in launching heavier spacecraft.
A Mission That Revives an Old Story
EOS-5 also has a connection with one of the GSLV programme’s major setbacks. In August 2021, GSLV-F10 was launched with EOS-03, an Earth observation satellite intended to provide capabilities broadly similar to those now planned for EOS-5.
The initial stages of the flight went as planned. The mission, however, failed when the indigenous cryogenic upper stage did not ignite properly. EOS-03 was consequently lost. EOS-5 now represents another attempt to establish advanced imaging capabilities from a much higher orbit.
The satellite weighs around 2,367 kilograms and is designed to operate from geosynchronous orbit. GSLV-F17 will initially place it into a Sub Geosynchronous Transfer Orbit, following which the spacecraft will be manoeuvred towards its operational position.
Why the Orbit Matters
The biggest advantage of EOS-5 is its ability to remain focused on the same broad region of Earth. Satellites operating in low Earth orbit move rapidly around the planet and observe a location at intervals. A geosynchronous satellite, by contrast, can maintain a much more persistent view of a particular area.
For India, that could translate into continuous observations of weather systems, cloud activity, cyclones and environmental conditions. The data could also support disaster management, infrastructure monitoring and surveillance of strategically important areas.
Such a capability is increasingly valuable as extreme weather events become more disruptive and the need for rapid information during floods, cyclones, droughts and forest fires grows.
The Machine Behind the Mission
GSLV-F17 is a 51.7-metre-tall, three-stage rocket with a liftoff mass of approximately 420.5 tonnes. Its first stage combines a solid core with four liquid-fuel strap-on boosters. A liquid-fuelled second stage follows, while the final stage uses India’s indigenous cryogenic propulsion system.
The cryogenic stage will once again be under scrutiny during the mission, making the flight an important demonstration of the technology that helped establish India’s independent heavy-launch capability.
The GSLV Mk II has already carried major spacecraft into orbit and was selected for the launch of NISAR, a high-value civilian Earth observation mission developed by India and the United States.
A Crucial Flight for ISRO
The September 4 launch will consequently be watched for several reasons. EOS-5 is expected to provide a new type of Earth observation capability for India. The GSLV-F17 mission will also test the reliability of a launcher with a complicated history. And for ISRO, a smooth flight would come at a particularly valuable time following the recent PSLV setbacks.
The mission is not simply about putting another satellite into orbit. It is an opportunity for ISRO to demonstrate that its launch programme remains capable of recovering from setbacks and delivering complex missions. After years of development, failures and technological challenges, the “naughty boy” is once again preparing for liftoff. This time, it has a chance to turn a difficult chapter into a much-needed success.