Steady gaze: On the launch of the ISRO’s EOS-05 satellite
The GSLV-F17 mission carrying the EOS-05 Earth observation satellite lifted off from the Second Launch Pad at the Satish Dhawan Space Centre, Sriharikota
The 2,367-kg satellite was injected into a Sub-Geosynchronous Transfer Orbit (Sub-GTO) roughly 18–19 minutes after liftoff, from where it will use its own propulsion to reach its final geostationary slot at about 36,000 km altitude
EOS-05 carries multispectral and hyperspectral imaging payloads capable of observing a given region every 5 minutes and the entire Indian landmass roughly every 30 minutes
The mission is intended to support weather monitoring, agriculture and crop-health tracking, disaster management (floods, cyclones, forest fires), and border-area surveillance
GSLV and India's Indigenous Cryogenic Engine Story
The Geosynchronous Satellite Launch Vehicle (GSLV) is a three-stage Indian launch vehicle — a solid-fuel first stage with four liquid strap-on boosters, a liquid-fuel second stage, and a cryogenic third stage — developed specifically to place heavier payloads into geostationary transfer orbit than the PSLV can carry. Its cryogenic upper stage has a distinct geopolitical history: in 1991 ISRO signed a deal with the Soviet Union (later Russia) for cryogenic engines and technology, but the United States pressured Russia to cancel technology transfer in 1993–94, citing the Missile Technology Control Regime (MTCR), forcing India to develop its own cryogenic engine indigenously.
Key Details
- Indigenous Cryogenic Upper Stage Project formally began in 1994; the engine developed is designated CE-7.5 (7.5-tonne thrust class)
- GSLV-D5 (January 2014) was the first fully successful flight using the indigenous CE-7.5 engine, placing GSAT-14 in orbit — making India the sixth country with operational cryogenic engine capability
- GSLV Mk III (now called LVM3) uses a more powerful indigenous CE-20 cryogenic engine and is a separate, larger vehicle used for missions like Chandrayaan-3
- GSLV-F17 used the standard GSLV Mk II configuration with the CE-7.5 cryogenic stage
EOS-05, at 2,367 kg, is described as the heaviest payload the GSLV has carried to date, illustrating incremental improvements in the indigenous cryogenic stage's performance since the 1990s technology-denial episode.
EOS-05 and ISRO's Earth Observation Satellite (EOS) Naming System
ISRO adopted a unified "EOS" (Earth Observation Satellite) numbering convention in 2020 for all its remote-sensing satellites, replacing the earlier series-specific names such as RISAT, Cartosat, and GISAT. Under this scheme, satellites are numbered sequentially by launch order regardless of which specialised sub-series (radar imaging, cartographic, or geostationary imaging) they belong to.
Key Details
- The renaming began with RISAT-2BR2, which was redesignated EOS-01 (launched November 2020)
- EOS-05 is technically the second satellite in ISRO's GISAT (Geostationary Imaging Satellite) sub-series; the first attempt, then called GISAT-1 (also designated EOS-03), was lost when the GSLV-F10 mission failed on 12 August 2021 after the cryogenic stage did not ignite due to a pressure drop in the liquid hydrogen tank
- RISAT-series satellites use Synthetic Aperture Radar (SAR) for all-weather, day-night imaging, distinct from EOS-05's optical multispectral/hyperspectral sensors, which require clear sky conditions
EOS-05's successful placement in orbit effectively completes the geostationary imaging capability that India first attempted — and lost — in the 2021 GSLV-F10 failure, restoring continuous, near-real-time observation of the Indian subcontinent from a fixed vantage point.
Orbit Classification: LEO, GTO, Sub-GTO and Geostationary Orbit
Satellites are launched first into a transfer orbit and then raised to their operational orbit using onboard propulsion. A Geosynchronous Transfer Orbit (GTO) is a highly elliptical orbit with its farthest point (apogee) near the geostationary altitude of about 35,786 km; a "Sub-GTO," as used for EOS-05, has a lower apogee than a standard GTO, requiring the satellite's own thrusters to perform additional orbit-raising manoeuvres to reach the final geostationary orbit — a technique that lets the launch vehicle carry a heavier payload than a direct-to-GTO injection would allow.
Key Details
- Geostationary orbit: circular, equatorial, at approximately 35,786–36,000 km altitude, with an orbital period matching Earth's rotation (24 hours), making the satellite appear stationary over a fixed point
- Geosynchronous orbit is the broader category (any orbit with a 24-hour period, not necessarily equatorial or circular); all geostationary orbits are geosynchronous, but not all geosynchronous orbits are geostationary
- Using a Sub-GTO trades a heavier payload for a longer, fuel-intensive orbit-raising phase — GSLV has previously used this approach for other GEO-bound payloads
EOS-05's Sub-GTO injection explains why the satellite needed further onboard manoeuvres over subsequent days to reach its intended geostationary slot at around 36,000 km, rather than being placed there directly by the launch vehicle.
Multispectral vs Hyperspectral Remote Sensing
Multispectral sensors capture a scene in a limited number of broad wavelength bands (visible, near-infrared, etc.), while hyperspectral sensors capture hundreds of narrow, contiguous spectral bands, allowing much finer discrimination of materials, minerals, vegetation types, and soil conditions based on their unique spectral signatures.
Key Details
- EOS-05 carries VNIR (Visible and Near-Infrared) and SWIR (Short-Wave Infrared) hyperspectral imagers with over a hundred spectral bands each, in addition to a multispectral/long-wave infrared payload
- Hyperspectral imaging is used for precision agriculture (crop stress detection), mineral exploration, and environmental monitoring — applications that a standard multispectral or panchromatic (single broad-band, high-resolution) sensor cannot perform as precisely
- India's Cartosat series uses high-resolution panchromatic/multispectral sensors for mapping, distinct from the spectral-analysis role of hyperspectral payloads like EOS-05's
The hyperspectral capability is what allows EOS-05 to monitor crop health and soil moisture with a level of material-specific detail that ordinary optical Earth observation satellites cannot achieve.
- Launch: GSLV-F17/EOS-05 mission, Second Launch Pad, Satish Dhawan Space Centre, Sriharikota
- Satellite mass: 2,367 kg — the heaviest payload flown on a GSLV to date
- Orbit: injected into Sub-Geosynchronous Transfer Orbit; final operational orbit at approximately 36,000 km (geostationary)
- Imaging cadence: specific region every 5 minutes; full Indian landmass every ~30 minutes
- Payloads: multispectral, hyperspectral (VNIR and SWIR bands), and long-wave infrared imagers
- Predecessor GISAT-1/EOS-03 was lost in the GSLV-F10 launch failure of 12 August 2021 (cryogenic stage ignition failure)
- India's indigenous cryogenic engine (CE-7.5) first flew successfully on GSLV-D5 in January 2014, after the US-driven cancellation of the original 1991 Indo-Russian cryogenic technology transfer deal