PSLV Launches Space Observatory ASTROSAT

IAS Prelims 2023

In its 31st flight (PSLV-C30), India’s Polar Satellite Launch Vehicle successfully launched ASTROSAT, the country’s Multi Wavelength Space Observatory along with six foreign customer satellites into a 644.6 X 651.5 km orbit inclined at an angle of 6 deg to the equator. The achieved orbit is very close to the intended one. This was the 13th consecutive success for PSLV.

PSLV was launched today in its heaviest ‘XL’ version with six strap-on motors of the first stage. The launch took place from the First Launch Pad at the Satish Dhawan Space Centre SHAR (SDSC SHAR), Sriharikota, the spaceport of India.

The 320 tonne, 45 m tall PSLV-C30 carrying seven satellites including the 1513 kg ASTROSAT, lifted off at 10:00 Hrs IST. About twenty two minutes after lift-off, ASTROSAT was successfully placed in orbit and separated from the fourth stage of PSLV-C30. The separation of all the six co-passenger satellites was completed in the subsequent three minutes. The seven satellites carried by PSLV-C30 together weighed about 1631 kg at lift-off.

After a 50 hour smooth count down, the 320 ton PSLV-C28 was launched with the ignition of its first stage. The important flight events included:

  • the ignition and separation of the strap-ons,
  • separation of the first stage,
  • ignition of the second stage,
  • separation of the payload fairing after the vehicle had cleared the dense atmosphere,
  • second stage separation,
  • third stage ignition and third stage separation,
  • fourth stage ignition and fourth stage cut-off.


Through 30 successful flights during 1994-2015 period, PSLV has launched a total of 84 satellites including these seven satellites. The vehicle has repeatedly proved its reliability and versatility by successfully launching satellites into a variety of orbits including polar Sun Synchronous, Geosynchronous Transfer and Low Earth orbits of small inclination thereby emerging as the workhorse launch vehicle of India.

So far, 51 satellites have been launched by PSLV for customers from abroad. This latest launch of six co-passenger satellites by PSLV-C30 was facilitated by Antrix Corporation Limited, the commercial arm of the Indian Space Research Organisation (ISRO), a government of India Company under the Department of Space (DOS).

Soon after its separation from PSLV-C30, the two solar arrays of ASTROSAT were automatically deployed and the Spacecraft Control Centre at the Mission Operations Complex of ISRO Telemetry, Tracking and Command Network (ISTRAC) at Bangalore took control of ASTROSAT.


ASTROSAT was realised by ISRO with the participation of all major astronomy institutions including:

  • Inter University Centre for Astronomy and Astrophysics (IUCAA) of Pune,
  • Tata Institute of Fundamental Research (TIFR) at Mumbai,
  • Indian Institute of Astrophysics (IIAP) and
  • Raman Research Institute (RRI) of Bangalore as well as some of the Universities in India and two institutions from Canada and the UK.

ASTROSAT is India’s first dedicated multi wavelength space observatory. This scientific satellite mission endeavours for a more detailed understanding of our universe. One of the unique features of ASTROSAT mission is that it enables the simultaneous multi-wavelength observations of various astronomical objects with a single satellite.

ASTROSAT will observe universe in the optical, Ultraviolet, low and high energy X-ray regions of the electromagnetic spectrum, whereas most other scientific satellites are capable of observing a narrow range of wavelength band. Multi-wavelength observations of ASTROSAT can be further extended with co-ordinated observations using other spacecraft and ground based observations. All major astronomy Institutions and some Universities in India will participate in these observations.

ASTROSAT has a lift-off mass of about 1513 kg. The science data gathered by five payloads of ASTROSAT are telemetered to the ground station at MOX. The data is then processed, archived and distributed by Indian Space Science Data Centre (ISSDC) located at Byalalu, near Bangalore.

The scientific objectives of ASTROSAT mission are:

  1. To understand high energy processes in binary star systems containing neutron stars and black holes
  2. Estimate magnetic fields of neutron stars
  3. Study star birth regions and high energy processes in star systems lying beyond our galaxy
  4. Detect new briefly bright X-ray sources in the sky
  5. Perform a limited deep field survey of the Universe in the Ultraviolet region

Payloads of ASTROSAT :

Five payloads of ASTROSAT are chosen to facilitate a deeper insight into the various astrophysical processes occurring in the various types of astronomical objects constituting our universe. These payloads rely on the visible, Ultraviolet and X-rays coming from distant celestial sources.

  1. The Ultraviolet Imaging Telescope (UVIT, capable of observing the sky in the Visible, Near Ultraviolet and Far Ultraviolet regions of the electromagnetic spectrum
  2. Large Area X-ray Proportional Counter (LAXPC, is designed for study the variations in the emission of X-rays from sources like X-ray binaries, Active Galactic Nuclei and other cosmic sources.
  3. Soft X-ray Telescope (SXT) is designed for studying how the X-ray spectrum of 0.3-8 keV range coming from distant celestial bodies varies with time.
  4. Cadmium Zinc Telluride Imager (CZTI), functioning in the X-ray region, extends the capability of the satellite to sense X-rays of high energy in 10-100 keV range.
  5. Scanning Sky Monitor(SSM), is intended to scan the sky for long term monitoring of bright X-ray sources in binary stars, and for the detection and location of sources that become bright in X-rays for a short duration of time.