ISRO's GSLV-F17 puts EOS-05 into orbit after a seven-month launch gap

The Indian Space Research Organisation launched EOS-05 on GSLV-F17 from the Second Launch Pad at Satish Dhawan Space Centre, Sriharikota, at 2:55 a.m. on Friday, 4 September. Eighteen minutes later the 2,367-kilogram satellite separated into a sub-geosynchronous transfer orbit. Prime Minister Narendra Modi called it India's first imaging satellite from geosynchronous orbit.

The flight ended a launch drought of nearly seven months. PSLV-C61 failed on 18 May 2025 during third-stage burn with EOS-09 on board. PSLV-C62 failed on 12 January 2026 shortly before third-stage separation. Friday's success was ISRO's first launch of 2026 and the 19th flight of the GSLV. The rocket, 51.7 metres tall with a lift-off mass of 420.5 tonnes, used the indigenous CUS15 cryogenic upper stage.

Mission planners had aimed for a transfer orbit of about 171 by 28,934 kilometres at 19.28 degrees. The upper stage delivered more energy than the plan. Apogee came out near 31,026 kilometres, about 2,092 kilometres higher than the target. That extra height means EOS-05 will burn less of its own fuel raising itself to a geosynchronous working orbit near 36,000 kilometres. For a spacecraft that must keep station and point cameras for years, leftover propellant is lifetime.

EOS-05 replaces EOS-03, also called GISAT-1, which was lost when GSLV-F10's cryogenic stage failed in August 2021. The new satellite is built to stare at large parts of the Indian landmass from high orbit rather than sweep it from low Earth orbit. ISRO has four EOS-series craft working in LEO, two of them with radar that can see through cloud. EOS-05 adds a different product: repeated looks at the same wide area, with spatial resolution around 42 metres, useful for floods, cyclone watches, agriculture and disaster rooms that need the same scene refreshed through a day.

GSLV earned the shop-floor nickname "Naughty Boy" after a run of early failures. On this flight the third stage behaved. That matters for the next heavy civil and navigation loads that still depend on this vehicle while a newer fleet matures. ISRO has already listed EOS-10, an oceansat follow-on, as a possible March 2027 launch. A working geosynchronous imager is the missing piece those later missions assume is already on station.

Earth observation from GEO is common for weather satellites. It is less common for land imaging, because distance blurs detail. Forty-two metres will not read a street. It will show a river leaving its banks, a burn scar spreading, or a reservoir dropping through a dry month. Combined with the low-orbit radar pair, the desk in a flood state can hold both a wide still picture and a cloud-piercing close look.

The satellite now has days of orbit-raising burns ahead. Each firing will be watched for the same reason the launch was watched: the last time this class of payload left the pad, it did not arrive. If EOS-05 reaches slot and opens its instruments, the seven-month silence of 2026 becomes a date on a timeline rather than a verdict on the launcher.

Sriharikota's night launch also returns a simple industrial fact. A cryogenic stage that lights when it should is still the constraint on India's medium-heavy civil missions. Friday morning, it lit.