POLIX Onboard XPoSat: An Indian X-ray Polarimeter Instrument
0:05 Introduction: The talk focuses on the POLIX (Indian X-ray Polarimeter) instrument aboard the XPoSat (X-ray Polarimeter Satellite), a collaborative project between the Raman Research Institute (RRI) and ISRO.
0:47 X-ray Polarimetry Context: POLIX is the second X-ray polarimeter in space, following NASA's IXPE, and operates in the 8-30 keV energy band. Both instruments study polarization properties of celestial X-ray sources.
1:22 POLIX Uniqueness: POLIX employs a unique design with proportional counter-based detectors and utilizes the satellite's rotation for observations.
3:00 Need for Space-Based Observation: X-rays are absorbed by Earth's atmosphere, necessitating space-based instruments like POLIX to study them.
3:32 POLIX Development: POLIX was developed entirely at RRI in collaboration with ISRO.
3:42 POLIX Objectives: The instrument measures the degree and angle of polarization of X-rays, providing insights into magnetic fields, emission processes, and geometry of celestial sources.
4:11 Principle of Operation: POLIX utilizes anisotropic Thomson scattering of X-ray photons by a low atomic mass scatterer (beryllium). The scattering probability is higher perpendicular to the electric field vector of the incoming photon.
4:35 Modulation from Polarized Sources: Polarized X-ray sources exhibit modulation in photon counts, while unpolarized sources show a uniform count.
5:02 Detector Configuration: POLIX has four position-sensitive proportional counters arranged cyclically around the scatterer.
5:29 Mechanical Configuration: The instrument includes a scatterer, four detectors, a collimator to restrict the field of view (3° x 3°), and a rotating mechanism.
6:19 POLIX Specifications: Key specifications include a photon collection area of 640 cm², 8-30 keV energy range, 130 kg weight, 5-year lifetime, and a data generation rate of 6.5 Gbps per day.
7:39 Detector Construction: Detectors are multi-wire proportional counters filled with Xenon gas at 800 Torr.
8:28 Collimator: The collimator is an aluminum block with 757 hexagonal tapered holes.
8:57 Scatterer: The scatterer is made of beryllium.
9:15 Azimuthal Distribution: Polarization measurement relies on determining the azimuthal distribution of photons hitting the detectors as the instrument rotates.
9:50 Electronics System: The electronics system comprises front-end electronics, processing electronics, common electronics, housekeeping, and telemetry, tracking, and command (TT&C) components.
10:21 Block Diagram: The block diagram illustrates the signal flow from the detectors through various electronics stages to the satellite bus. Redundancy is implemented in the common electronics and TT&C sections.
14:27 Electronics Development History: The development started with lab versions using locally available components, progressing to space-qualified versions with components tested for extreme temperatures and vibrations.
15:52 Space-Qualified Model: The final flight model was manufactured by Centum Electronics, an ISRO-certified vendor.
16:46 Qualification Model (QM): A qualification model was built and tested to ensure the system's performance under space-like conditions.
17:22 Flight Model (FM): The flight model was assembled and tested rigorously before integration with the satellite.
18:08 Testing at ISRO: Extensive tests, including thermal vacuum, vibration, and electromagnetic compatibility (EMC) tests, were conducted at ISRO facilities.
18:37 Integration with Satellite: POLIX was integrated onto the XPoSat satellite bus, and further tests were performed.
18:49 Pre-Shipment Test: Integrated satellite pre-shipment tests were conducted before the satellite's transfer to the Sriharikota spaceport.
19:27 Launch and Orbit: XPoSat was launched on 1st January 2024 into a low Earth orbit with an altitude of 650 km and a 6° inclination.
19:58 Data Verification: Data from POLIX was continuously verified during all tests and found to be satisfactory.