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India’s First Polarimetry Mission XPoSat


The X-Ray Polarimeter Satellite (XPoSat), due for launch later this year, is being built by the Indian Space scientific Organisation in partnership with the Raman Research agency (RRI), Bengaluru, an independent scientific agency.


GS Paper-3: Science and Technology- developments and their applications and effects in everyday life

Mains Question

In what ways has India’s X-Ray Polarimeter Satellite (XPoSat) project contributed to the development of astrophysics? Describe the idea of polarimetry and how it helps us comprehend bright astronomical X-ray sources better. (150 words)


  • The ISRO states that “XPoSat will study various dynamics of bright astronomical X-ray sources in extreme conditions.”
  • It has been hailed as the world’s second polarimetry mission and the first in India. Its goal is to learn more about the dynamics of bright astronomical X-ray sources in difficult circumstances.The NASA Imaging X-ray Polarimetry Explorer (IXPE), which was launched in 2021, is the other such important mission.

Understanding the X-Rays in Space

  • Understanding X-Rays in Space According to NASA, X-rays have substantially higher energies and shorter wavelengths, ranging from 0.03 to 3 nanometers, which makes some of them little larger than a single atom of several elements.
  • The wavelength of radiation that an object emits depends on its physical temperature. The peak emission wavelength gets shorter as an object gets hotter.X-rays are produced by objects with temperatures in the millions of degrees Celsius, such as black holes, pulsars, and relics of galactic supernovae.

The Importance of Polarimetry

  • The Importance of Polarimetry X-rays are made up of travelling electric and magnetic waves, much like all other types of light. These waves’ peaks and dips typically go in arbitrary directions.
  • According to a NASA video on IXPE, polarised light is better ordered because it has two different types of waves that vibrate in the same direction.
    • It further states that while near water, fishermen wear polarised lenses to lessen glare from the sun.
  • According to Britannica, the science of polarimetry examines the measurement of the rotational angle of a plane of polarised light, or a beam of light in which the vibrations of electromagnetic waves are contained within a single plane. This phenomenon occurs when light passes through certain transparent materials.

ISRO’s XPoSat Initiative

  • According to the ISRO website, space-based observatories are unable to provide information about the precise nature of the emissions from various astronomical sources, including black holes, neutron stars, active galactic nuclei, pulsar wind nebulae, etc.
  • The emission mechanism from these sources originates from complex physical processes and is difficult to understand. As a result, more modern equipment is needed to measure particular qualities.

XPoSat payload

  • Two research payloads will be carried by the XPoSat spacecraft in a low Earth orbit. The polarimetry parameters (degree and angle of polarisation) will be measured by the primary payload, POLIX (Polarimeter Instrument in X-rays).
  • RRI is working with ISRO’s U R Rao Satellite Centre (URSC) in Bengaluru to create the payload.
    • POLIX is anticipated to observe over 40 brilliant astronomical objects of various types over the course of the XPoSat mission’s anticipated lifespan of around 5 years.
    • This is the first polarimetry-focused payload in the medium X-ray energy band.
  • Spectroscopic data (on how light is absorbed and emitted by objects) will be provided by the XSPECT (X-ray Spectroscopy and Timing) payload. It would keep an eye on a variety of sources, including neutron stars with low magnetic fields, black hole binaries, and X-ray pulsars.


  • India’s attempt to launch the X-Ray Polarimeter Satellite (XPoSat) is an important turning point in the nation’s ambitions to conduct space research.
    • By utilising polarimetry techniques, XPoSat will provide invaluable insights into the nature and behaviour of these celestial objects, including black holes, neutron stars, and pulsars. o The mission aims to study the dynamics of bright astronomical X-ray sources in extreme conditions.
    • POLIX and XSPECT, the scientific payloads on board, will allow precise measurements of polarimetry parameters and spectroscopic data.
  • As XPoSat gets ready to launch, it promises to deepen our understanding of the cosmos and make significant contributions to the field of astrophysics.

September 2023