ISRO begins countdown for GSLV-F17 launch with Earth observation satellite

The countdown for the launch of an Earth observation satellite aboard a GSLV rocket began at the spaceport of Sriharikota in neighbouring Andhra Pradesh, the Indian Space Research Organisation (ISRO) said on Thursday.

The GSLV-F17 is scheduled to lift off from the second launch pad at the Satish Dhawan Space Centre in Sriharikota, about 135 km east of Chennai, at 2.55am on Friday, carrying the Earth Observation Satellite-05 (EOS-05) into a sub-geosynchronous transfer orbit (Sub-GTO).

The 27.5-hour countdown for the mission began at 11.25pm on September 2, ISRO sources told HT.

Dubbed the ‘eye in the sky’ for its ability to monitor the Earth from an altitude of 36,000 km, the GSLV-F17 will be the 19th flight of the Geosynchronous Satellite Launch Vehicle. It will also be the first imaging satellite to be placed in a sub-geosynchronous orbit, unlike earlier missions that used geosynchronous orbits, ISRO said.

The GSLV, at a height of 51.7 metres, has a lift-off mass of 420.5 tonnes. It is a three-stage vehicle with a cryogenic upper stage.

The GSLV-F17/EOS-05 mission is a follow-up to the GSLV-F10/Earth Observation Satellite-03, which was ‘unsuccessful’ as it suffered a cryogenic upper-stage ignition failure after lift-off on August 12, 2021, at 5.43am from Sriharikota.

The GSLV rocket would fly with a 4-metre-diameter ogive composite payload fairing and is expected to place the satellite, weighing 2,367 kg, at an altitude of 36,000 km.

At this height, the satellite’s orbit synchronises with the rotation of the Earth, ensuring it stays at a fixed place. The satellite would provide repeated images of India and neighbouring regions.

The Geosynchronous Satellite Launch Vehicle with a cryogenic upper stage is intended to carry heavier satellites weighing 2,200 kg to be placed into Geosynchronous Transfer Orbits (GTOs).

The objective of Friday’s mission is to provide near-real-time imaging of large-area regions at frequent intervals for quick monitoring of natural disasters and episodic events, and to obtain spectral signatures for agriculture, forestry and waterbodies, ISRO said.

The Earth Observation Satellite would also share information for disaster warning, cyclone monitoring, cloudburst and thunderstorm monitoring, ISRO said.

The previous GSLV mission launched by ISRO was GSLV-F16/NISAR on July 30, 2025. It is the first-of-its-kind mission jointly developed by ISRO and NASA to image global land and ice-covered surfaces, including islands, sea ice and selected oceans, every 12 days.