Most space telescopes watch the sky in one kind of light. ASTROSAT watches in four at once, from a single satellite that has now outlived its planned lifespan twice over.
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Science and Technology · SciTech0103
ASTROSAT
India’s Eyes on Four Kinds of Light
28 Sep 2015
Launched on PSLV-C30, India’s first multi-wavelength space observatory.
2020
UVIT detects UV light from a galaxy 9.3 billion light-years away.
28 Sep 2025
Completes ten years in orbit — twice its planned mission life.
4 Dec 2025
IIA marks 10 years of UVIT: 1,451 targets, ~300 papers, 19 PhDs.
One Platform, Four Kinds of Light
Most observatories watch the sky in a single band. ASTROSAT observes visible, ultraviolet, and both soft and hard X-rays, simultaneously, from one satellite.
🏛️ Must Know
ASTROSAT’s Basic Facts
- ASTROSAT is India’s first dedicated multi-wavelength space astronomy observatory. It was launched on 28 September 2015, aboard a PSLV-C30 rocket, from the Satish Dhawan Space Centre, Sriharikota.
- It carries five scientific instruments. These are the Ultra-Violet Imaging Telescope (UVIT), the Soft X-ray Telescope (SXT), and the Large Area X-ray Proportional Counters (LAXPC). The remaining two are the Cadmium Zinc Telluride Imager (CZTI) and the Scanning Sky Monitor (SSM).
- ASTROSAT can observe the same cosmic source simultaneously in visible light, ultraviolet light, and both low- and high-energy X-rays.
- The satellite weighs about 1,513 kg, and orbits Earth at an altitude of roughly 650 km.
- Its sanctioned cost was ₹177.85 crore. Its designed mission life was five years, but it remains fully operational well beyond that.
- UVIT, the satellite’s ultraviolet payload, was designed and built by the Indian Institute of Astrophysics (IIA). It had support from ISRO centres, IUCAA, TIFR, and the Canadian Space Agency.
📘 Good to Know
What ASTROSAT Has Discovered
- ASTROSAT’s ability to study different parts of the electromagnetic spectrum from one platform sets it apart from most other space observatories, which typically observe in only one band.
- In 2020, UVIT detected extreme-ultraviolet light from a galaxy called AUDFS01, located about 9.3 billion light-years away.
- ASTROSAT data has shown a black hole in the binary system 4U 1630-17 spinning near the maximum speed physics allows.
- In 2024, ASTROSAT data helped reveal new details about the internal structure of neutron stars, some of the densest known objects in the universe.
- Its X-ray payloads also detected polarised X-rays from the Crab Pulsar’s off-pulse region, and its instruments have tracked star formation inside so-called “Jellyfish galaxies.”
- ISRO periodically invites Indian and international astronomers to propose new ASTROSAT observations, through what it calls an Announcement of Opportunity cycle.
📝 Previous Year Questions
UPSC CSP 2016 — What’s Actually True About ASTROSAT
- UPSC 2016 Neither “India is the only country besides USA/Russia with a similar observatory” nor “Astrosat is a 2000 kg satellite at 1650 km” is correct. Its real mass is about 1,513 kg and its real orbit is about 650 km, and other countries such as Japan and the ESA have flown comparable observatories. See UPSC CSP 2016 GS Paper I, Q87. View this question.
Test Yourself
🌟 Great to Know
ASTROSAT’s Legacy and What’s Next
- ASTROSAT completed ten years of continuous operation on 28 September 2025, twice its original planned mission life.
- ASTROSAT is developed and operated by ISRO (the Indian Space Research Organisation), alongside its better-known launch-vehicle and satellite work.
- ISRO has floated a possible successor mission, informally called AstroSat-2. As of 2026, it remains in early planning, with no confirmed payload suite or launch date.
- Scientists have separately discussed a still-larger future space telescope, called INSIST (Indian Spectroscopic and Imaging Space Telescope), building on the experience gained from UVIT.
📰 Current Affairs
Latest ASTROSAT Developments
- On 4 December 2025, the Indian Institute of Astrophysics held a workshop marking ten years of UVIT’s operation aboard ASTROSAT. UVIT first opened its doors on 30 November 2015. (Source: PIB)
- Over that decade, UVIT observed a total of 1,451 targets in the sky, leading to about 300 research articles and 19 PhD theses. (Source: PIB)
- IIA Director Annapurni Subramaniam noted that UVIT remains one of very few operational telescopes capable of observing in the far-ultraviolet band. The only other one is the Hubble Space Telescope. (Source: PIB)
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