ISRO’s advanced earth observation satellite launched successfully
The GSLV-F17 rocket lifted off from the Satish Dhawan Space Centre, Sriharikota, and successfully placed the EOS-05 Earth observation satellite into its intended sub-geosynchronous transfer orbit around 18 minutes after launch.
EOS-05 (also called GISAT-1A) is described by ISRO as India's first imaging satellite designed for eventual operation from a geosynchronous-type orbit, carrying advanced multi-spectral and hyperspectral imaging payloads.
The mission is the 19th flight of the Geosynchronous Satellite Launch Vehicle (GSLV) and used the vehicle's indigenous cryogenic upper stage for the final orbit-raising burn.
The successful placement strengthens India's Earth observation capability for applications spanning weather monitoring, disaster management, and agriculture.
GSLV and India's Indigenous Cryogenic Technology
The Geosynchronous Satellite Launch Vehicle (GSLV) is ISRO's three-stage launch vehicle built to place heavier satellites into Geosynchronous Transfer Orbit (GTO), a task beyond the lighter PSLV's normal capability. Its first stage is a solid booster (S139) augmented by four liquid strap-on motors; the second stage is a liquid-fuelled stage; the third is a Cryogenic Upper Stage (CUS) burning liquid hydrogen and liquid oxygen. India became the sixth country to master indigenous cryogenic engine technology, ending reliance on the Russian-supplied cryogenic stage used in early GSLV Mark I flights.
Key Details
- GSLV is roughly 51.7 m tall with a lift-off mass of about 420 tonnes.
- The indigenous Cryogenic Upper Stage first flew successfully on GSLV-D5 in January 2014, carrying GSAT-14.
- Versions using the Russian-supplied cryogenic stage are classified GSLV Mark I; those with the indigenous stage are GSLV Mark II.
- GSLV Mark III (now called LVM3) is a separate, heavier-lift vehicle used for larger geostationary payloads and crewed missions such as Gaganyaan.
EOS-05 was launched on GSLV-F17, the 19th flight of this vehicle, using the same indigenous cryogenic stage lineage that has become central to India's self-reliance in space launch capability.
Geosynchronous vs. Geostationary vs. Sub-GTO: Orbit Classification
UPSC frequently tests the distinction between orbit types used in satellite launches. A geosynchronous orbit is any orbit whose period matches Earth's rotation period (about 23 hours 56 minutes), placing the satellite at an altitude of roughly 35,786 km; it can have any inclination relative to the equator. A geostationary orbit is a special case of geosynchronous orbit with zero inclination and zero eccentricity directly above the equator, so the satellite appears fixed over one point on Earth. A Geosynchronous Transfer Orbit (GTO) is an elliptical intermediate orbit used to transfer a satellite from low Earth orbit up to geosynchronous altitude; a "sub-GTO" is a transfer orbit with a lower apogee than a standard GTO, requiring the satellite's own onboard propulsion to complete the climb to its final operational altitude.
Key Details
- Geostationary/geosynchronous altitude: approximately 35,786 km above the equator.
- Orbital period at this altitude equals one sidereal day.
- Every geostationary satellite is geosynchronous, but not every geosynchronous satellite is geostationary (inclination and eccentricity determine the difference).
- Placing a satellite in sub-GTO rather than full GTO is a launch-vehicle performance trade-off; the satellite uses its own thrusters to raise the orbit further after separation.
ISRO confirmed EOS-05 was placed in a sub-geosynchronous transfer orbit, meaning the satellite will use its own propulsion system to complete the transition toward its final near-geosynchronous working orbit, from which it can repeatedly image large swathes of the Earth.
Earth Observation Satellites and the EOS/GISAT Series
India's Earth Observation Satellite (EOS) series (successor naming to older IRS and GISAT designations) covers satellites built for applications like agriculture, disaster management, forestry, and strategic surveillance using optical, multi-spectral, and hyperspectral sensors. EOS-05/GISAT-1A follows an earlier attempt, GISAT-1 (also designated EOS-03), whose GSLV-F10 launch failed in August 2021 due to a leaking valve that caused a pressure drop in the cryogenic stage's liquid hydrogen tank, preventing the vehicle from reaching orbit.
Key Details
- EOS-03/GISAT-1 failure (August 2021): anomaly occurred roughly 350 seconds into flight due to a vent and relief valve leak in the cryogenic stage.
- A geosynchronous imaging satellite offers near-real-time, repeated observation of a large fixed region, useful for quick disaster and agricultural monitoring, unlike polar-orbiting satellites that pass over a given location only periodically.
- EOS-05 is designed to capture images at short intervals to support near-continuous monitoring.
EOS-05/GISAT-1A represents ISRO's successful follow-up attempt at putting an Indian geosynchronous imaging satellite into orbit, five years after the 2021 GISAT-1/EOS-03 failure on a similar GSLV vehicle.
- Launch vehicle: GSLV-F17 (19th flight of GSLV).
- Satellite: EOS-05, also known as GISAT-1A.
- Orbit achieved: sub-geosynchronous transfer orbit, roughly 18 minutes after lift-off.
- Launch site: Satish Dhawan Space Centre, Sriharikota, Andhra Pradesh.
- Geosynchronous/geostationary altitude reference: approximately 35,786 km.
- Predecessor failure: GISAT-1/EOS-03 on GSLV-F10, August 2021.