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Imaging X-ray Polarimetry Explorer
Imaging X-ray Polarimetry Explorer.jpg
An artist's impression of IXPE. On the right are its three identical X-ray optics elements, the sensors are on the left.
Mission typeX-ray astronomy satellite
OperatorNASA / Italian Space Agency
Mission duration2 years (planned)
Spacecraft properties
ManufacturerBall Aerospace
Launch mass337 kg [1]
Payload mass170 kg
Start of mission
Launch dateAugust 2021
RocketFalcon 9 [2]
Launch siteKSC, LC-39A
Orbital parameters
Reference systemGeocentric orbit
RegimeLow Earth orbit
Perigee altitude540 km
Apogee altitude540 km
Inclination0.2° (Equatorial)
Main telescope
Focal length4 m [3]
BandS-band [4]

The Imaging X-ray Polarimetry Explorer, commonly known as IXPE, is a space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays.[5] The mission will study exotic astronomical objects and permit mapping the magnetic fields of black holes, neutron stars, pulsars, supernova remnants, magnetars, quasars, and active galactic nuclei. The high-energy X-ray radiation from these objects' surrounding environment can be polarized – vibrating in a particular direction. Studying the polarization of X-rays reveals the physics of these objects and can provide insights into the high-temperature environments where they are created.[6]


The IXPE mission was announced on 3 January 2017.[5] It is being developed by NASA's Small Explorer program (SMEX) and is slated for launch in August 2021.[7] The estimated cost of the mission and its two-year operation is US$188 million (the launch cost is US$50.3 million).[8][6] The goal of the IXPE mission is to expand understanding of high-energy astrophysical processes and sources, in support of NASA's first science objective in astrophysics: "Discover how the universe works".[1] By obtaining X-ray polarimetry and polarimetric imaging of cosmic sources, IXPE addresses two specific science objectives: to determine the radiation processes and detailed properties of specific cosmic X-ray sources or categories of sources; and to explore general relativistic and quantum effects in extreme environments.[1][5]

During IXPE's two-year mission, it will study targets such as active galactic nuclei, quasars, pulsars, pulsar wind nebulae, magnetars, accreting X-ray binaries, supernova remnants, and the Galactic Center.[3]

The spacecraft is being built by Ball Aerospace.[1] The principal investigator is Martin C. Weisskopf of NASA Marshall Space Flight Center; he is the chief scientist for X-ray astronomy at NASA's Marshall Space Flight Center and project scientist for the Chandra X-ray Observatory spacecraft.[6]

International collaboration[edit]

The IXPE mission is an international collaboration signed on June 2017.[1] The X-ray polarization detectors will be provided by the Italian Space Agency (ASI).[6] Other partners include the University of Colorado Boulder, Stanford University, McGill University in Canada, MIT (Massachusetts Institute of Technology)[1] and OHB Italia.[9]


The technical and science objectives include:[10]

  • Improve polarization sensitivity by two orders of magnitude over the X-ray polarimeter aboard the Orbiting Solar Observatory 8.
  • Provide simultaneous spectral, spatial, and temporal measurements.
  • Determine the geometry and the emission mechanism of active galactic nuclei and microquasars.
  • Find the magnetic field configuration in magnetars and determine the magnitude of the field.
  • Find the mechanism for X-ray production in pulsars (both isolated and accreting) and the geometry.
  • Determine how particles are accelerated in pulsar wind nebula.


Telescope (x3) Basic parameters
Wavelength X-ray
Energy range 2–8 keV
Field of view (FOV) >11′
Angular resolution ≤30″

The space observatory features three identical telescopes designed to measure the polarization of cosmic X-rays.[5] The polarization sensitive detector was invented and developed by Italian scientists of the Istituto Nazionale di AstroFisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) and was refined over several years.[3][11][12]


IXPE's payload is a set of three identical imaging X-ray polarimetry systems mounted on a common optical bench and co-aligned with the pointing axis of the spacecraft.[1] Each system operates independently for redundancy, and comprises a 4-meter focal length mirror module assembly that focuses X-rays onto polarization-sensitive imaging detector developed in Italy.[1] The focal length is achieved using a deployable boom.

The Gas Pixel Detectors (GPD) utilize the anisotropy of the emission direction of photoelectrons produced by polarized photons to gauge with high sensitivity the polarization state of X-rays interacting in a gaseous medium.[3] Position-dependent and energy-dependent polarization maps of such synchrotron-emitting sources will elucidate the magnetic field structure of the X-ray emitting regions. X-ray polarimetric imaging better indicates the magnetic structure in regions of strong electron acceleration. The system is capable to resolve point sources from surrounding nebular emission or from adjacent point sources.[3]

See also[edit]


  1. ^ a b c d e f g h "IXPE (Imaging X-ray Polarimetry Explorer)". eoPortal. ESA. Retrieved 17 February 2019.
  2. ^ "NASA Awards Launch Services Contract for Groundbreaking Astrophysics Mission" (Press release). NASA. 8 July 2019. This article incorporates text from this source, which is in the public domain.
  3. ^ a b c d e Weisskopf, Martin C.; Ramsey, Brian; o'Dell, Stephen L.; Tennant, Allyn; Elsner, Ronald; Soffitta, Paolo; Bellazzini, Ronaldo; Costa, Enrico; Kolodziejczak, Jeffery; Kaspi, Victoria; Muleri, Fabio; Marshall, Herman; Matt, Giorgio; Romani, Roger (2016). "The Imaging X-ray Polarimetry Explorer (IXPE)". Results in Physics. 6: 1179–1180. Bibcode:2016ResPh...6.1179W. doi:10.1016/j.rinp.2016.10.021.
  4. ^ "IXPE Fact Sheet" (PDF). NASA. 2017. This article incorporates text from this source, which is in the public domain.
  5. ^ a b c d NASA Selects Mission to Study Black Holes, Cosmic X-ray Mysteries. Karen Northon, NASA News. 3 January 2017 This article incorporates text from this source, which is in the public domain.
  6. ^ a b c d NASA selects X-ray astronomy mission. Jeff Foust, Space News. 4 January 2017
  7. ^ "Coronavirus work stoppage likely to delay launch of NASA X-ray astronomy mission". Spaceflight Now. 2 July 2020. Retrieved 3 July 2020.
  8. ^ Clark, Stephen (8 July 2019). "SpaceX wins NASA contract to launch X-ray telescope on reused rocket". Spaceflight Now.
  9. ^ Presentation: Advanced Observatory Design for the Imaging X-Ray Polarimeter Explorer (IXPE) Mission
  10. ^ "IXPE: Expanding the X-ray View of the Universe". NASA. 2017. This article incorporates text from this source, which is in the public domain.
  11. ^ Costa, Enrico; Soffitta, Paolo; Bellazzini, Ronaldo; Brez, Alessandro; Lumb, Nicholas; Spandre, Gloria (2001). "An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars". Nature. 411: 662–665. Bibcode:2001Natur.411..662C. doi:10.1038/35079508.
  12. ^ Bellazzini, R.; Spandre, G.; Minuti, M.; Baldini, L.; Brez, A.; Latronico, L.; Omodei, N.; Razzano, M.; Massai, M. M.; Pesce-Rollins, M.; Sgrò, C.; Costa, E.; Soffitta, P.; Sipila, H.; Lempinen, E. (2017). "A sealed Gas Pixel Detector for X-ray astronomy". Nuclear Instruments and Methods in Physics Research Section A. 592 (2): 853–858. arXiv:astro-ph/0611512. Bibcode:2007NIMPA.579..853B. doi:10.1016/j.nima.2007.05.304.