Steady gaze: On the launch of the ISRO’s EOS-05 satellite

EOS-05 (previously designated GISAT-1A) was launched aboard the GSLV-F17 rocket. Operating from a geosynchronous orbit about 36,000 kilometres above Earth, it provides continuous real-time imaging of the Indian subcontinent, unlike conventional low-earth orbit satellites that only pass overhead periodically.

Launch vehicles typically inject heavy communication and imaging satellites into an intermediate elliptical orbit known as a Geosynchronous Transfer Orbit (GTO). The satellite then fires its own onboard propulsion system (Liquid Apogee Motor) in multiple stages over several weeks to circularize its path into a permanent orbit 36,000 km above the equator.

Unlike standard cameras that capture only visible light (RGB), remote sensing satellites carry multispectral and hyperspectral sensors. These instruments detect reflected electromagnetic radiation across invisible bands (such as near-infrared and shortwave infrared), enabling precise differentiation between healthy crops, water bodies, dry soil, and urban structures.

In satellite remote sensing, there is a fundamental trade-off between spatial resolution (the physical clarity visible per pixel) and temporal resolution (how often a satellite can re-image the same spot). Low Earth Orbit (LEO) satellites (500–800 km) capture sharp, sub-meter details but take days to return to the same location, whereas Geosynchronous satellites (36,000 km) offer lower spatial detail but provide continuous observation with revisit cycles of minutes.

The INSAT-3D series (comprising INSAT-3D, INSAT-3DR, and INSAT-3DS) consists of dedicated meteorological satellites operated by ISRO in geostationary orbit (36,000 km). Equipped with atmospheric sounders and multispectral imagers, they monitor weather systems, sea surface temperatures, atmospheric humidity, and cyclone development across the Indian Ocean.

A Sun-Synchronous Polar Orbit (SSPO) is a special low-altitude orbit (typically 500–800 km) where the satellite passes over the poles and maintains a constant angle relative to the Sun. As a result, the satellite crosses any given latitude at the exact same local solar time every day, ensuring identical lighting and shadow conditions essential for comparing agricultural changes and urban growth over time.

Low Earth Orbit (LEO) imaging satellites observe Earth along a narrow ground path known as a swath (ranging from 10 km to a few hundred km wide). Because Earth rotates beneath the satellite’s fixed orbital plane, each 90-minute orbit captures an adjacent slice of the planet, requiring between 4 to 22 days for a single satellite to revisit and photograph the exact same coordinates.

In late August 2026, a catastrophic glacial avalanche near the Nepal-Tibet border triggered a massive debris flow into the Bhote Koshi and Trishuli rivers, destroying vital bridges, roads, and hydropower projects, and claiming over 1,300 lives. Continuous high-temporal satellite observation enables geoscientists to detect early warning signs such as moraine-dam expansion, glacial lake swelling, and slope deformation before catastrophic Glacial Lake Outburst Floods (GLOFs) or landslides occur.

Polar-orbiting satellites like NASA’s MODIS (Aqua/Terra) and ISRO’s polar fleet pass over northern India at fixed times (typically around 10:30 AM and 1:30 PM). Studies found that some farmers shifted farm-fire timing to late afternoons or evenings to avoid detection during orbital flyovers. A geosynchronous satellite with continuous monitoring eliminates these temporal blind spots.

In aerospace terminology, strategic satellites refer to dual-use platforms that serve both civilian and national security purposes. While providing data for meteorology, disaster relief, and agriculture, continuous high-orbit imaging also provides real-time surveillance of sensitive border areas (Line of Actual Control and Line of Control) and the Indian Ocean Region.

The utility of Earth Observation (EO) satellites depends heavily on downstream data processing and dissemination. Under India’s National Geospatial Policy, ISRO makes satellite data available via platforms like Bhoonidhi and Bhuvan, allowing academic researchers, meteorological bodies, defense agencies, and private geospatial startups to convert raw sensor feeds into real-time weather models, agricultural advisories, and disaster alerts.

In August 2021, the GSLV-F10 mission carrying the EOS-03 (GISAT-1) satellite failed when its indigenous Cryogenic Upper Stage (CUS) failed to ignite during the third-stage flight due to a drop in chamber pressure. The successful launch of EOS-05 aboard GSLV-F17 marks a major redemption and validation of ISRO’s indigenous cryogenic engine technology.

The Polar Satellite Launch Vehicle (PSLV), known as ISRO’s most reliable workhorse with over 55 successful missions since 1993, suffered two unprecedented consecutive failures: PSLV-C61 on May 18, 2025, and PSLV-C62 on January 12, 2026. Failure analysis committees identified pressure anomalies and motor casing disturbances during the third solid-fuel stage (PS3) burns as the primary causes.