A screengrab of GSLV's Cryogenic Upper Stage (CUSP) injecting EOS-05 into a precise orbit

ISRO’s GSLV-F17 rocket has outperformed expectations, placing EOS-05 into a higher-than-planned orbit with an apogee of 31,026 km instead of 28,934 km.

This improved performance means the satellite will conserve fuel during orbit-raising, likely extending its mission life beyond the planned seven years.

The GSLV-F17 mission was designed to place EOS-05 into a Sub-Geosynchronous Transfer Orbit. The expected apogee was 28,934 km, but the cryogenic third stage delivered an apogee of 31,026 km, exceeding projections by 2,092 km.

This achievement is significant because EOS-05, weighing 2,367 kg, is heavier than the 2,250 kg maximum payload GSLV can deliver to a standard Geostationary Transfer Orbit.

EOS-05 is India’s first imaging satellite designed to operate from geosynchronous orbit. Ideally, such satellites are launched into an elliptical 170 × 35,786 km Geostationary Transfer Orbit.

From there, they use onboard propulsion to raise the perigee and circularise into a Geostationary Orbit at 35,786 km altitude. However, due to the payload mass exceeding GSLV’s GTO capacity, ISRO opted for a burn-to-depletion strategy, exhausting all cryogenic propellant to send the satellite as far as possible.

The higher apogee achieved means EOS-05 will now require less of its own propellant to reach geosynchronous orbit. This conservation of fuel is critical because the remaining propellant will be available for station-keeping and attitude control once the satellite is operational.

Station-Keeping ensures the satellite remains fixed relative to Earth’s rotation, while attitude control maintains its orientation for imaging and communication.

By saving fuel during orbit-raising, EOS-05 is expected to extend its mission life beyond the planned seven years. This extended operational period will enhance India’s ability to conduct continuous Earth observation, disaster monitoring, cyclone tracking, flood assessment, forest fire detection, agricultural planning, and environmental studies. It will also provide persistent monitoring over strategically important regions.

The mission is a milestone for ISRO’s GSLV program. EOS-05 is the heaviest satellite ever launched by GSLV into a Sub-GTO orbit, demonstrating the improved performance of India’s indigenous cryogenic stage.

The rocket’s lift-off mass was 420.5 tons, and this was its 19th flight. The success boosts confidence in India’s ability to place heavier payloads into geosynchronous orbit, a capability crucial for advanced communication, meteorology, and strategic surveillance.

EOS-05’s successful injection into a higher orbit also highlights ISRO’s engineering refinements. The cryogenic stage has evolved significantly since its early flights, now capable of delivering payloads beyond its nominal design limits.

This achievement strengthens India’s position in space technology and enhances its strategic autonomy in Earth observation.

The satellite will now perform a series of orbit-raising manoeuvres using its onboard propulsion system. Once it reaches its final geosynchronous orbit, EOS-05 will provide India with a continuous eye in the sky, capable of monitoring the same region repeatedly from nearly 36,000 km above Earth.

Agencies