Launch vehicles, satellites and applications

Prelims and Mains

Geosynchronous orbit is new ground for Indian Earth observation, and EOS-05 is the first to image from it. Which orbit a satellite is given decides what its pictures can show and how often they arrive, so the choice is made against what the images are for.

• A Geosynchronous Satellite Launch Vehicle (GSLV-F17) carried EOS-05 to orbit.
• Also called Geo Imaging Satellite 1A (GISAT-1A), it images chosen areas at frequent intervals for disaster monitoring, agriculture and forestry.
• It replaces GISAT-1, lost in 2021 when the cryogenic upper stage of its GSLV failed to ignite.
• A satellite in low Earth orbit sees fine detail, but its revisit time runs to days.
• A satellite in geosynchronous orbit watches one large region continuously, in coarser detail, and spends fuel on station keeping.
• Only a satellite in geostationary orbit appears fixed in the sky, while other geosynchronous orbits trace a path across it over the day.
• What these satellites see feeds the Landslide Atlas of India, the monitoring of glacial lake outburst floods, and the National Database for Emergency Management 5.0.

Background reading: The Indian Express, 5 Sep 2026: ISRO launches EOS-05: What are the different types of satellite orbits, and why do they matter? (opens in a new tab)

Prelims and Mains

Prelims asks what each mission was first to do, which is why this is worth holding as a list rather than as a history. Besides EOS-05 and Aditya-L1 above, these are the missions ISRO has recently flown and those it has approved or planned.

• Chandrayaan-3 made the first soft landing near the lunar south pole, on 23 August 2023.
• XPoSat is India's first X-ray polarimetry mission.
• SPADEX (Space Docking Experiment) made India the fourth country to dock two spacecraft in orbit.
• NISAR (NASA-ISRO Synthetic Aperture Radar), flown with the National Aeronautics and Space Administration (NASA) of the United States, is the first Earth observation satellite to carry radar in both the L and S bands.
• GSAT-7R (CMS-03) is a communications satellite for the Navy.
• The Venus Orbiter Mission is planned.
• Chandrayaan-4 is to bring a lunar sample back to Earth.
• LUPEX (Lunar Polar Exploration), also called Chandrayaan-5, is planned with the Japan Aerospace Exploration Agency (JAXA).

Prelims and Mains

The cycle an engine runs on decides how much of its propellant ends as thrust, and how hard the engine is to build. Full-flow staged combustion is the demanding end of that choice, which is why so few countries have flown it.

• A Bengaluru startup unveiled Everest, an 800 kN engine, making India the fourth country with full-flow staged combustion technology after Russia, the United States and China.
• It burns liquid oxygen and methane, a pair called methalox that leaves little soot.
• The cycle throttles precisely and suits reusable rockets.