XPoSat (X-ray Polarimeter Satellite) is India’s first dedicated polarimetry mission to study various dynamics of bright astronomical X-ray sources in extreme conditions. The spacecraft will carry two scientific payloads in a low earth orbit. The primary payload POLIX (Polarimeter Instrument in X-rays) will measure the polarimetry parameters (degree and angle of polarization) in medium X-ray energy range of 8-30 keV photons of astronomical origin. The XSPECT (X-ray Spectroscopy and Timing) payload will give spectroscopic information in the energy range of 0.8-15 keV.

The emission mechanism from various astronomical sources such as blackhole, 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. The polarimetry measurements add two more dimension to our understanding, the degree of polarization and the angle of polarization 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. This would be the major direction of research from XPoSat by Indian science community.

XPoSat payloads:

1. POLIX is an X-ray Polarimeter for astronomical observations in the energy band of 8-30 keV. The payload is being developed by Ramam Research Institute (RRI), Bangalore in collaboration with U R Rao Satellite Centre (URSC). The instrument is made of a collimator, a scatterer and four X-ray proportional counter detectors that surrounds the scatterer. The scatterer is made of low atomic mass material which causes anisotropic Thomson scattering of incoming polarised X-rays. The collimator restricts the field of view to 3 degree x 3 degree so as to have only one bright source in the field of view for most observations. POLIX is expected to observer about 40 bright astronomical sources of different categories during the planned lifetime of XPoSat mission of about 5 years. This is the first payload in the medium X-ray energy band dedicated for polarimetry measurements.

2. XSPECT is an X-ray SPECtroscopy and Timing payload onboard XPoSat, which can provide fast timing and good spectroscopic resolution in soft X-rays. Taking advantage of the long duration observations required by POLIX to measure X-ray polarization, XSPECT can provide long-term monitoring of spectral state changes in continuum emission, changes in their line flux and profile, simultaneous long term temporal monitoring of soft X-ray emission in the X-ray energy range 0.8-15 keV. An array of Swept Charge Devices (SCDs) provide an effective area >30 cm2 at 6 keV with energy resolution better than 200 eV at 6 keV. Passive collimators are used to reduce the background by narrowing the field of view of XSPECT. XSPECT would observe several types of sources viz X-ray pulsars, blackhole binaries, low-magnetic field neutron star (NS) in LMXBs, AGNs and Magnetars.

Credit: ISRO

PSLV-DL

The Polar Satellite Launch Vehicle - DL (PSLV-DL) is the two side-mounted solid rocket booster configuration of the overall PSLV family of expendable rockets flown by the Indian Space Research Organisation (ISRO).

It was built to fill the payload launch gap in capabilities between the PSLV-Core Alone (no side-mounted solid rocket boosters) and PSLV-QL (four boosters).

The rocket also reduces the cost of science and defence mission launches.

Its first flight occurred on January 24th, 2019 when it took the Microsat-R Earth observation satellite to space for the Indian Department of Defence.

The rocket uses a mixture of solid and liquid propellant stages to get to orbit. The first stage, also called the core, is a solid propellant rocket, and the two side-mounted solid propellant boosters are bolted to it.

A liquid fueled second stage then takes over, followed by a third stage that is powered by solid propellant.

A liquid fueled fourth stage serves as the final part of the rocket. The engines on this stage are restartable to place satellites into their proper orbits.

Image: PSLV-DL. Credit: ISRO

Satish Dhawan Space Centre or Sriharikota Range is a rocket launch center operated by the Indian Space Research Organisation. It is located in Sriharikota in Andhra Pradesh.

Chosen for its remote location, the center became operational in 1971 and hosted its first launch that year for a suborbital mission.

The first orbital launch took place on August 10, 1979.

The spaceport received its current name in 2005 when it was named in honor of Satish Dhawan, the former head of the Indian Space Research Organisation.

The facility has two launch pads and will be the base of India's upcoming human spaceflight program.

Image: ISRO