XPoSAT MISSION

XPoSAT MISSION OVERVIEW

XPoSat is designed to function in a Low Earth Orbit at an altitude of approximately 650 km, featuring a low inclination of around 6 degrees.

• The satellite is equipped with two advanced payloads, facilitating comprehensive studies of X-ray sources. These payloads focus on exploring temporal, spectral, and polarization characteristics.
• Primary goals of XPoSat include measuring X-ray polarization within the 8-30 keV energy range. Additionally, it aims to conduct extended studies in the 0.8-15 keV band.
• XPoSat is anticipated to remain operational for an estimated 5-year mission lifespan.
• The satellite will primarily conduct observations during Earth’s eclipse period, optimizing operational efficiency.
• XPoSat will be India's third space-based observatory, following the recently launched solar mission Aditya-L1 and AstroSat, which was launched in 2015.

MAIN GOALS OF XPoSAT

Studying X-Rays

• XPoSat will examine X-rays, which are a type of light that’s invisible to us but comes from various cosmic sources like stars and black holes.
• Focuses on the medium energy band (8-30 keV).

2. Understanding black holes and other celestial objects

• By analyzing these X-rays, scientists aim to gain insights into the behavior and properties of black holes and other astronomical phenomena.

3. Additional Parameters

• POLIX will measure the degree and angle of polarisation of X-ray photons.
• These parameters, along with spectrographic, timing, and imaging data, will enhance researchers' understanding of celestial bodies.
• SIGNIFICANCE OF XPoSAT MISSION

1. X-ray polarisation measurements in medium energy bands for the first time

• So far, polarisation of celestial sources was done either in the optical or radio bands.
• XPoSat, however, will facilitate X-ray polarisation measurements possible from bright sources, that too, in the medium energy band (8-30 keV) energy range.
• This has never been attempted ever before.

2. Analyse two kinds of sources

• XPoSat will observe two kinds of sources like  persistent sources (targeted and known sources) and transient sources (pulsars, active galactic nuclei, magnetars).

3. Nature of the radiations and the multitudes of processes involved can be analysed

• Out in space, X-rays get polarised due to multiple causes.
• For example, X-rays when subject to strong magnetic fields or due to the interactions with material present around black holes.
• With the help of XPoSat, scientists can now probe the nature of the radiations and the multitudes of processes involved in the generation of these radiations.

4. Will aid the researchers by analysing the additional parameters

• POLIX will undertake important measurements like the degree and angle of polarisation of X-ray photons from various potential sources.
• These two additional parameters, along with the spectrographic, timing and imaging data, will aid researchers to overall improve the present understanding of the celestial bodies.

KEY PAYLOADS IN XPoSAT

POLIX (Polarimeter Instrument in X-rays)

• Functionality

• POLIX is designed to operate in the medium X-ray energy band of 8 to 30 kilo electron Volts (keV).

• Components

• It comprises a collimator, which filters light from bright sources, and a scatterer with four X-ray proportional counter detectors that prevent trapped light from escaping.

• Observation targets

• POLIX is expected to observe a few tens of astronomical sources, particularly during specific celestial events like magnetars or neutron stars transiting through Earth's shadow.

2. XSPECT (X-ray Spectroscopy and Timing)

• Functionality

• XSPECT is designed for fast timing and high spectroscopic resolution in the soft X-ray energy band ranging from 0.8 to 15 keV.

• Observation targets

• XSPECT aims to observe a variety of sources, including X-ray pulsars, black hole binaries, low-magnetic field neutron stars, active galactic nuclei (AGNs), and magnetars.

HIGHLIGHT OF MISSION

1. After the launch, PS4 stage underwent two restarts for orbit adjustment to a stable 350 km circular orbit, ensuring a stable 3-axis mode for Orbital Platform (OP) experiments.
2. This mission includes the PSLV Orbital Experimental Module-3 (POEM-3) aiming to accommodate and execute 10 payloads contributed by ISRO and Indian National Space Promotion and Authorization Center (IN-SPACe).
3. The Satellite configuration is modified from the IMS-2 (Small Satellite Bus) bus platform. 
4. The mainframe systems configuration is based on IRS (Indian Remote Sensing) satellites.

PSLV-C58

• The PSLV C-58 was the 60th flight of the Indian Space Research Organisation's Polar Satellite launch Vehicle.
• It carried the XPoSAT mission along with rideshare payloads.

POLARISATION OF X-RAYS AND THEIR STUDY

X-rays comprises of electric and magnetic waves which are constantly in motion.

• Due to their sinusoidal wave nature, they tend not to follow a patterned direction of motion.
• But a polarised X-ray is both organised and has two waves vibrating in the similar direction.
• Measuring the polarization of X-rays using instruments like POLIX enables astronomers to understand the orientation and strength of magnetic fields in celestial objects. 
• This, in turn, provides crucial insights into the nature and behaviour of pulsars, regions around black holes, and other cosmic phenomena emitting X-rays

SCOPE OF XPoSAT

The emission mechanism from various astronomical sources such as black hole, neutron stars, active galactic nuclei, pulsar wind nebulae, etc originates from complex physical processes and are challenging to understand.

• While the spectroscopic and timing information by various space based observatories provide a wealth of information, the exact nature of the emission from such sources still poses deeper challenges to astronomers. 
• Polarimetry measurements offer an excellent diagnostic tool for comprehending the emission processes from various astronomical sources.
• By combining polarimetric observations with spectroscopic and timing measurements, researchers anticipate overcoming the limitations of present understanding of astronomical emission processes. 
• The polarimetry measurements add two more dimensions to our understanding, the degree of polarisation and the angle of polarisation and thus is an excellent diagnostic tool to understand the emission processes from astronomical sources. 
• The polarimetric observations along with spectroscopic measurements are expected to break the degeneracy of various theoretical models of astronomical emission processes.

COMPARISON WITH GLOBAL X-RAY MISSIONS

Previous Indian Mission  AstroSat

• AstroSat, launched in 2015, performed timing and broadband spectroscopy of X-ray sources but did not include polarisation studies.

2. Global Missions

• Few missions worldwide focused on X-ray polarisation measurements, including NASA's Imaging X-ray Polarimetry Explorer (IXPE) launched in 2021 (2 to 8 keV energy band).
• Some like HX-POL and XL-Calibur have been balloon-based and short-duration experiments by NASA and collaborators.