ISRO launches EOS-05, India's 1st imaging satellite in geosynchronous orbit : GS TIMES IAS-PCS

Why in News?

The Indian Space Research Organisation (ISRO) launched EOS-05, India’s first dedicated imaging satellite designed to operate in geosynchronous orbit, on 4 September using the GSLV-F17 rocket from the Satish Dhawan Space Centre.

Nickname: “Eye in the Sky”
Launch vehicle: GSLV-F17
Mass: 2,367 kg
It is described as India’s heaviest Earth-observation satellite.
Unlike Earth-observation satellites in LEO that periodically revisit locations, EOS-05’s geosynchronous positioning allows continuous observation of the same broad region.

Why Use Geosynchronous Orbit?

A heavy satellite cannot easily be placed directly into its final geosynchronous orbit because doing so would require a very large amount of rocket fuel. Therefore, ISRO follows a multi-stage orbital transfer strategy: GSLV → Sub-GTO → Satellite’s own propulsion → GEO/GSO

GSLV places the satellite into a sub-geosynchronous transfer orbit (sub-GTO).
EOS-05 then uses its on-board propulsion to raise its orbital altitude, circularise its orbit, reduce orbital inclination and reach its operational orbit.

The GSLV-F17 placed EOS-05 in a sub-GTO at an altitude of more than 190 km.

Understanding Earth’s Major Orbits

Low Earth Orbit (LEO)

Generally extends from about 160 km to 2,000 km above Earth’s surface.
Satellites typically complete one revolution in around 90–120 minutes.
Relatively low signal latency because of proximity to Earth.
Widely used for:
- Earth observation
- Communication
- Scientific missions
- Satellite constellations
International Space Station (ISS) operates in LEO.
VLEO (Very Low Earth Orbit) and SSO (Sun-synchronous orbit) are important orbital configurations associated with LEO.

Medium Earth Orbit (MEO)

Approximately 2,000 km to 35,786 km.
Provides a compromise between coverage and signal latency.
Used extensively by global navigation satellite systems (GNSS).
Example: Galileo satellites operate in MEO.

Geosynchronous Orbit (GSO)

Around 35,786 km altitude.
Orbital period matches Earth’s rotation—approximately 24 hours.
A satellite in GSO generally moves west to east like Earth’s rotation.
Its position can appear stationary or trace a repeating pattern relative to Earth, depending on its inclination and eccentricity.

Geostationary Orbit (GEO)

GEO is a special case of GSO. For a satellite to be geostationary, it must: