Why is Isro launching the EOS-05 satellite nearly 35,000 km above Earth?

Isro will launch EOS-05 aboard GSLV-F17 on 4 September into a Sub-GTO. The mission aims to place India's first imaging satellite in geosynchronous orbit for more frequent regional observation.From geosynchronous orbit, nearly 36,000 km above Earth, the satellite can remain synchronised with Earth's rotation and repeatedly observe the same large region. (Photo: India Today)The Indian Space Research Organisation (Isro) is preparing to launch one of its most ambitious Earth-observation and imaging satellites yet, EOS-05, aboard the GSLV-F17 rocket on September 4 at 2:55 am IST.The mission will mark the first time India places an imaging satellite in geosynchronous orbit, allowing it to continuously watch vast regions of Earth from an altitude of nearly 36,000 kilometres.But before EOS-05 reaches its final operational position, the GSLV-F17 rocket will place the spacecraft into what Isro calls a Sub-Geosynchronous Transfer Orbit, or Sub-GTO. Gisat-1 ahead of integration with the GSLV. (Photo: Isro) GSLV-F17, the 19th flight of India's Geosynchronous Satellite Launch Vehicle, will lift off from the Second Launch Pad at the Satish Dhawan Space Centre in Sriharikota. The rocket will fly in its four-metre-diameter ogive composite payload fairing configuration. WHAT IS A SUB-GTO?A Geosynchronous Transfer Orbit (GTO) is essentially a temporary pathway that helps carry a satellite from near Earth towards its final operating position almost 36,000 kilometres above the planet.Instead of travelling in a perfect circle around Earth, a satellite in this transfer orbit follows an elongated, oval-shaped path. During each orbit, it comes close to Earth at one point and travels much farther away at another. This allows the rocket to send the spacecraft towards its final destination gradually. A Sub-Geosynchronous Transfer Orbit, or Sub-GTO, works on the same principle, but the rocket does not carry the satellite all the way to the altitude normally reached in a standard GTO. Instead, it releases the spacecraft at a lower, less energetic orbit, from where the satellite completes the rest of its journey using its own onboard engines. Graphic: Nasa In the case of EOS-05, the satellite is expected to be placed in an orbit where its closest point to Earth, known as the perigee, is around 170 kilometres above the planet. Its farthest point, known as the apogee, will be approximately 28,934 kilometres above Earth.SATELLITE WILL FLY ON ITS OWNThe Sub-GTO is still thousands of kilometres short of the satellite's final geosynchronous operating altitude of around 35,786 kilometres above the equator.After separating from the GSLV-F17 rocket, EOS-05 is expected to fire its onboard propulsion system several times to gradually raise and reshape its orbit.The process will eventually place the satellite into its final geosynchronous orbit, where it will travel around Earth at the same rate as the planet rotates.From this high vantage point, EOS-05 will be able to repeatedly observe the same broad region of Earth, unlike low-Earth-orbit satellites that quickly move over different parts of the planet.WHY SEND AN IMAGING SATELLITE SO HIGH?Most Earth-observation satellites operate from low Earth orbit, typically a few hundred kilometres above the planet. While they can capture highly detailed images, they move rapidly relative to Earth's surface and can observe a particular location only during periodic passes.EOS-05 is designed to change that.From geosynchronous orbit, nearly 36,000 km above Earth, the satellite can remain synchronised with Earth's rotation and repeatedly observe the same large region.This gives India the ability to monitor the Indian subcontinent and surrounding areas far more frequently than conventional polar-orbiting imaging satellites.Isro describes EOS-05 as India's first-ever imaging satellite from geosynchronous orbit. The capability could support weather monitoring, disaster response, cyclone tracking, floods, forest fires, agriculture and environmental observation, while also providing persistent monitoring over strategically important regions.The Sub-GTO trajectory is therefore the first step in a carefully planned orbital journey. Instead of placing EOS-05 directly at its final altitude, GSLV-F17 will deliver it into an elliptical transfer orbit, allowing the spacecraft to complete the climb using its own propulsion.If successful, the September 4 mission will give India a new eye in space, one positioned almost 36,000 km above Earth and capable of watching the same region far more continuously than conventional Earth-observation satellites.- EndsPublished By: Sibu Kumar TripathiPublished On: Sep 2, 2026 12:26 IST