India’s Unblinking Eye: EOS-05 Returns to High-Altitude Skies

ISRO is launching the EOS-05 satellite, a second attempt after the GISAT-1 mission failed in 2021. This advanced Earth observation satellite will be placed in a geostationary orbit, 36,000 km above the equator. From this fixed position, it will provide near real-time, continuous monitoring of India.

Five years ago, in August 2021, a GSLV-F10 rocket lifted off from Sriharikota carrying a satellite India had waited years to see in orbit. It never reached its intended home. GISAT-1, short for Geo Imaging Satellite, was lost when the rocket ran into trouble during its climb, and with it went a bold idea: that India could station a camera high above the equator and watch its own land without a pause.

That idea is about to get its second chance. On September 4, at 2.55 in the morning, GSLV-F17 is scheduled to rise from the Second Launch Pad at the Satish Dhawan Space Centre, carrying EOS-05, an advanced Earth observation satellite built to finish what GISAT-1 could not. For the Indian Space Research Organisation (ISRO), whose engineers lived through the 2021 setback, this countdown carries a weight that goes far beyond routine.

What makes EOS-05 unusual is where it will live. Most Earth observation satellites circle the planet at low altitudes, sweeping over a place only briefly before moving on, like a bus that passes your stop a few times a day. EOS-05 will instead sit roughly 36,000 kilometres above the equator, in what is called geostationary orbit. At that height, a satellite travels around Earth at exactly the pace at which Earth itself turns, so from the ground it appears to hang motionless over one spot, like a watchman on a tall tower rather than a patrol walking the streets. The rocket will not drop it straight there; it leaves the satellite in a stepping-stone orbit, from which it climbs the rest of the way on its own engine.

This steady perch (its fixed position high above the equator, always facing the same part of Earth) is what allows the satellite to photograph India and its neighbourhood over and over. Under the mission plan, EOS-05 will deliver near real-time pictures roughly every 30 minutes, and when a region demands closer attention, fresh images as often as every five minutes. A satellite in a lower orbit could never manage this, because it must complete its journey around the globe before its path brings it over India again. One caveat: like any camera it needs a clear view, so this works only under cloud-free skies; it cannot peer through monsoon cloud.

Why does such speed matter? Because disasters do not wait. A cyclone building in the Bay of Bengal, a river bursting its banks, a forest fire racing up a hillside: each can change shape within minutes, and relief agencies must see those changes as they happen. Beyond emergencies, Earth observation satellites help track clouds and weather, judge the health of crops, and record shifts in land and water. Strategically, a satellite that never looks away can keep continuous watch over sensitive areas, strengthening national security.

None of this is easy. Geostationary orbit has traditionally been reserved for communication and weather satellites. Taking sharp pictures of Earth's surface from 36,000 kilometres away is a different challenge altogether, rather like reading a signboard in Kanyakumari while standing in Kashmir. To manage it, EOS-05 carries a telescope with a 700 mm mirror, roughly the width of a car tyre, which gathers far more light than an ordinary camera lens and lets it see fine detail from that great distance. Behind the telescope sit two kinds of sensors. The multi-spectral sensor records light in a handful of broad colour bands, including some the human eye cannot see, much like a set of coloured filters that reveal, for instance, whether vegetation is healthy or stressed. The hyper-spectral sensor goes much further, slicing light into dozens of very narrow bands, so that every surface, be it wet soil, a particular crop, or a patch of oil on water, leaves its own signature, rather like a fingerprint. Together, they let the satellite not just photograph the land but read it. The satellite must cover an enormous area yet aim this telescope with extraordinary precision, holding perfectly still while the image is captured, since any tremble at that distance would blur the picture. Its images can show a large field or a coastline changing, though not a single house. Once in place, EOS-05 is designed to keep working for 10 years, a full decade of watching over India before its fuel and systems wear out. Mastering all this is a real engineering milestone for India's Earth observation programme.

Which is why the early hours of September 4 will be watched with held breath across ISRO. Every launch tests machines, but this one also tests the resolve of an organisation that lost a satellite and chose to build it again. If all goes to plan, EOS-05 will become something India has never had: a tireless eye in the sky, watching over the subcontinent almost without blinking.