Back-to-Back GSLV Successes: EOS-05 and NVS-03 Restore Confidence in ISRO's Cryogenic Rocket
ISRO's Geosynchronous Satellite Launch Vehicle (GSLV) has flown two successful missions in a row in 2026, after a difficult period for Indian launches.
GSLV-F17 launched EOS-05 (GISAT-1A), an earth observation satellite, on 4 September 2026 from Sriharikota. It placed the satellite in a sub-geosynchronous transfer orbit, from which the satellite climbs to its final orbit using its own thrusters. At about 2,367 kg, it was described as the heaviest satellite launched by a GSLV.
GSLV-F18 launched NVS-03, a navigation satellite for India's NavIC system, on 30 October 2026 from the Second Launch Pad at the Satish Dhawan Space Centre, Sriharikota. It reached a Geosynchronous Transfer Orbit (GTO) of about 170 km x 38,080 km; the high point (apogee) was about 1,000 km more than planned because the rocket performed better than expected.
These successes matter because of earlier setbacks: the GSLV's cryogenic stage failed to ignite on the GSLV-F10/EOS-03 mission in August 2021, NVS-02 (launched by GSLV-F15 in January 2025) could not reach its working orbit because a valve on the satellite did not open, and PSLV-C62 failed in January 2026.
NVS-03 carries an indigenous atomic clock and also broadcasts the L1 navigation signal, which makes NavIC easier to use in ordinary phones.
GSLV (Geosynchronous Satellite Launch Vehicle) Programme
The GSLV is ISRO's three-stage rocket built to carry heavier satellites (about 2 tonnes class) into a Geosynchronous Transfer Orbit (GTO), the first step towards the 36,000 km high orbit used by communication, weather and navigation satellites. Its top stage burns super-cold liquid hydrogen and liquid oxygen; this is called a cryogenic stage. India first bought this technology from Russia and later built its own after the Missile Technology Control Regime (MTCR) pressure of the 1990s blocked the transfer. The GSLV (Mk II) is different from the bigger LVM3 (earlier called GSLV Mk III), which carries about 4 tonnes to GTO.
Two successes in two months show that the GSLV's cryogenic upper stage, which failed in 2021, is now flying reliably again. This is important because NavIC replacement satellites (the NVS series) depend on the GSLV.
Orbit Classification: LEO, GTO, Sub-GTO and Geostationary Orbit
Satellites are placed in different orbits depending on their job. Low Earth Orbit (LEO) is close to Earth (up to about 2,000 km) and suits imaging and the space station. Geostationary Orbit (GEO) is about 35,786 km above the equator; a satellite there takes 24 hours to go around and so appears fixed over one spot, which suits communication and weather satellites. Rockets usually do not take a satellite straight to GEO. They drop it in an oval Geosynchronous Transfer Orbit (GTO), with a low point of a few hundred km and a high point near 36,000 km, and the satellite then fires its own engine to make the orbit round.
EOS-05 was heavy, so GSLV-F17 placed it in a sub-GTO and the satellite is climbing on its own. GSLV-F18 delivered NVS-03 to a GTO with an apogee about 1,000 km above plan, which slightly reduces the fuel the satellite must use.
NavIC (IRNSS): India's Regional Navigation Satellite System
NavIC (Navigation with Indian Constellation), earlier called the Indian Regional Navigation Satellite System (IRNSS), is India's own satellite navigation system, like a regional version of the American GPS. It covers India and an area of about 1,500 km around it. Its main goal is that India does not depend on a foreign-controlled system like GPS, especially during conflicts. Each satellite carries very accurate atomic clocks, because a navigation receiver finds its position by measuring tiny differences in signal travel time.
NVS-03 is a replacement satellite meant to restore NavIC's full strength after clock failures and the loss of NVS-02. Its successful launch on GSLV-F18 is a step towards a fully working Indian navigation system with phone-friendly L1 signals.
- GSLV-F17: 4 September 2026; EOS-05 (GISAT-1A); about 2,367 kg; placed in sub-GTO
- GSLV-F18: 30 October 2026; NVS-03; Second Launch Pad, Satish Dhawan Space Centre, Sriharikota (Andhra Pradesh)
- NVS-03 orbit: about 170.3 km x 38,080 km GTO; apogee about 1,000 km higher than planned
- NVS-03: indigenous atomic clock; adds L1 signal
- Past setbacks: GSLV-F10/EOS-03 (August 2021) cryogenic stage failure; NVS-02 (January 2025) stuck in transfer orbit (pyro valve); PSLV-C62 (January 2026) failure
- GSLV stages: solid S139 + 4 liquid strap-ons, Vikas second stage, Cryogenic Upper Stage
- NavIC: 7-satellite constellation; coverage India + about 1,500 km