"ISRO Places EOS-05 in Geosynchronous Orbit for Strategic Earth Imaging"
Geostationary Orbit (GEO)
circular, equatorial orbit at 35,786 km where satellite stays fixed over one point
Geosynchronous Orbit (GSO)
24-hour orbital period matching Earth's rotation; may be elliptical or inclined
India's earth observation satellite programme has evolved from low-Earth-orbit imaging satellites to higher-altitude platforms capable of near-continuous coverage. The GSLV (Geosynchronous Satellite Launch Vehicle) is ISRO's workhorse for placing heavier payloads into geosynchronous transfer orbits, from where onboard engines raise the satellite to its final position. Understanding why a satellite is placed in one orbit rather than another requires grasping the difference between two closely related but distinct orbital regimes: Geostationary Orbit (GEO) and Geosynchronous Orbit (GSO).
A geostationary orbit is a special case of a geosynchronous orbit. Both share the same orbital period as Earth's rotation, approximately 24 hours, meaning the satellite completes one orbit in the same time Earth completes one rotation. However, GEO is defined by two additional constraints: the orbit must be perfectly circular (eccentricity = 0) and must lie exactly on the equatorial plane (inclination = 0°). This combination keeps the satellite fixed over a single point on Earth's surface at all times, at an altitude of 35,786 km. A geosynchronous orbit, by contrast, shares the same 24-hour period but may be elliptical or inclined relative to the equator. A satellite in GSO therefore appears to trace a figure-eight path (called an analemma) over the same longitude band rather than hovering over one fixed point.
This GEO vs GSO distinction is directly relevant to India's NavIC (IRNSS) navigation constellation, which uses both orbit types: three satellites in GEO (fixed over the equator) and four in GSO (inclined, tracing figure-eight tracks). The hybrid architecture ensures continuous multi-satellite visibility over the Indian subcontinent and up to 1,500 km beyond its borders. EOS-05's orbital choice draws on the same engineering logic, a GSO placement is chosen deliberately, not as a fallback.
EOS-05 (also designated GISAT-1A) is India's first dedicated imaging satellite designed to operate from the geostationary belt. It was launched by GSLV F17 into a sub-geosynchronous transfer orbit (GTO) with a perigee of 171 km and an apogee of 31,000 km, slightly above the targeted 29,000 km apogee, reflecting a near-perfect launch performance. Onboard LAM (Liquid Apogee Motor) engine burns over successive days raised the orbit progressively. After two manoeuvres, the satellite reached a GSO of approximately 20,000 km perigee by 35,786 km apogee, and its final operational slot is 85.5° East longitude.
The decision to operate in GSO rather than the theoretically optimal GEO is significant. A perfectly circular GEO would keep the satellite permanently fixed over one equatorial point, maximising imaging consistency for weather monitoring. However, ISRO scientists indicated that GSO was deliberately chosen for EOS-05's mission profile. …
With reference to the Indian Regional Navigation Satellite System (IRNSS), consider the following statements :
1.IRNSS has three satellites in geostationary and four satellites in geosynchronous orbits.
2.IRNSS covers entire India and about 5500 sq. km beyond its borders.
3.India will have its own satellite navigation system with full global coverage by the middle of 2019.
Which of the statements given above is/are correct?
With reference to 'Astrosat', the astronomical observatory launched by India, which of the following statements is/are correct?
1.Other than USA and Russia, India is the only country to have launched a similar observatory into space.
2.Astrosat is a 2000 kg satellite placed in an orbit at 1650 km above the surface of the Earth.
Select the correct answer using the code given below.
Consider the following statements regarding orbital regimes used by ISRO satellites:
1.A geostationary orbit (GEO) requires an eccentricity of zero and an inclination of zero degrees relative to the equator.
2.A geosynchronous orbit (GSO) has the same orbital period as Earth's rotation but may be elliptical or inclined.
3.NavIC (IRNSS) uses three satellites in GSO and four satellites in GEO.
4.EOS-05 was placed in a geostationary orbit at 35,786 km altitude as its final operational orbit.
How many of the above statements are correct?
Which of the following correctly describes the difference between a geostationary orbit (GEO) and a geosynchronous orbit (GSO)?
Match the following ISRO satellites/missions with their correct description:
List I (Mission) — List II (Description)
A.EOS-05 (GISAT-1A) — 1. India's first space-based astronomical observatory
B.NVS-02 — 2. Navigation satellite that failed due to onboard engine not firing post-launch
C.EOS-03 (GISAT-1) — 3. Lost due to cryogenic upper stage failure of GSLV F10 in 2021
D.AstroSat — 4. India's first dedicated imaging satellite from the geostationary belt
Select the correct answer using the code given below:
With reference to EOS-05, consider the following statements:
1.It was launched by GSLV F17 into a sub-geosynchronous transfer orbit.
2.Its final operational orbit is a perfectly circular geostationary orbit at 35,786 km altitude.
3.The Indian Navy is among its identified primary users.
4.It is placed at the 85.5° East orbital slot.
Which of the statements given above is/are correct?
Assertion (A): A satellite in a geosynchronous orbit (GSO) with non-zero inclination does not remain fixed over a single point on Earth's surface.
Reason (R): A satellite's ground track is fixed only when its orbital period equals Earth's rotation period AND its orbit is both circular and equatorial.
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