Chandra X-ray Observatory

Chandra X-ray Observatory

Illustration of Chandra
Names Advanced X-ray Astrophysics Facility (AXAF)
Mission type X-ray astronomy
Operator NASA / SAO / CXC
COSPAR ID 1999-040B
SATCAT № 25867
Mission duration Planned: 5 years
Elapsed: 17 years, 4 months, 15 days
Spacecraft properties
Manufacturer TRW Inc.
Launch mass 4,790 kg (10,560 lb)[1]
Dimensions 13.8 × 19.5 m (45.3 × 64.0 ft)[1]
Power 2350 W[1]
Start of mission
Launch date July 23, 1999, 04:31 (1999-07-23UTC04:31Z) UTC
Rocket Space Shuttle Columbia (STS-93)
Launch site Kennedy LC-39B
Orbital parameters
Reference system Geocentric
Regime Highly elliptical
Semi-major axis 80,795.9 km (50,204.2 mi)
Eccentricity 0.743972
Perigee 14,307.9 km (8,890.5 mi)
Apogee 134,527.6 km (83,591.6 mi)
Inclination 76.7156°
Period 3809.3 min
RAAN 305.3107°
Argument of perigee 267.2574°
Mean anomaly 0.3010°
Mean motion 0.3780 rev/day
Epoch September 4, 2015, 04:37:54 UTC[2]
Revolution number 1358
Main telescope
Type Wolter type 1[3]
Diameter 1.2 m (3.9 ft)[1]
Focal length 10.0 m (32.8 ft)[1]
Collecting area 0.04 m2 (0.43 sq ft)[1]
Wavelengths X-ray: 0.12–12 nm (0.1–10 keV)[4]
Resolution 0.5 arcsec[1]

Great Observatories
 Compton Spitzer

The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space observatory launched on STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope, enabled by the high angular resolution of its mirrors. Since the Earth's atmosphere absorbs the vast majority of X-rays, they are not detectable from Earth-based telescopes; therefore space-based telescopes are required to make these observations. Chandra is an Earth satellite in a 64-hour orbit, and its mission is ongoing as of 2016.

Chandra is one of the Great Observatories, along with the Hubble Space Telescope, Compton Gamma Ray Observatory (1991–2000), and the Spitzer Space Telescope. The telescope is named after astrophysicist Subrahmanyan Chandrasekhar.[5]


In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to NASA by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the following year at Marshall Space Flight Center (MSFC) and the Smithsonian Astrophysical Observatory (SAO). In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein (HEAO-2), into orbit. Work continued on the AXAF project throughout the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. AXAF's planned orbit was changed to an elliptical one, reaching one third of the way to the Moon's at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle but put the observatory above the Earth's radiation belts for most of its orbit. AXAF was assembled and tested by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California.

STS-93 launches in 1999

AXAF was renamed Chandra as part of a contest held by NASA in 1998, which drew more than 6,000 submissions worldwide.[6] The contest winners, Jatila van der Veen and Tyrel Johnson (then a high school teacher and high school student, respectively), suggested the name in honor of Nobel Prize–winning Indian-American astrophysicist Subrahmanyan Chandrasekhar. He is known for his work in determining the maximum mass of white dwarf stars, leading to greater understanding of high energy astronomical phenomena such as neutron stars and black holes.[5]

Originally scheduled to be launched in December 1998,[6] the spacecraft was delayed several months, eventually being launched in July 1999 by Space Shuttle Columbia during STS-93. At 22,753 kilograms (50,162 lb), it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage Inertial Upper Stage booster rocket system needed to transport the spacecraft to its high orbit.

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from MIT and Northrop Grumman Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope's focal plane during passages.

Although Chandra was initially given an expected lifetime of 5 years, on September 4, 2001 NASA extended its lifetime to 10 years "based on the observatory's outstanding results."[7] Physically Chandra could last much longer. A study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years.[8] In July 2008, the International X-ray Observatory, a joint project between ESA, NASA and JAXA, was proposed as the next major X-ray observatory but was later cancelled.[9] ESA later resurrected the project as the Advanced Telescope for High Energy Astrophysics (ATHENA) with a proposed launch in 2028.[10]

Examples discoveries

Crew of STS-93 with a scale model

The data gathered by Chandra has greatly advanced the field of X-ray astronomy. Here are some examples of discoveries supported by observations from Chandra:

Technical description

CXO image of the brown dwarf TWA 5B

Unlike optical telescopes which possess simple aluminized parabolic surfaces (mirrors), X-ray telescopes generally use a Wolter telescope consisting of nested cylindrical paraboloid and hyperboloid surfaces coated with iridium or gold. X-ray photons would be absorbed by normal mirror surfaces, so mirrors with a low grazing angle are necessary to reflect them. Chandra uses four pairs of nested mirrors, together with their support structure, called the High Resolution Mirror Assembly (HRMA); the mirror substrate is 2 cm-thick glass, with the reflecting surface a 33 nm iridium coating, and the diameters are 65 cm, 87 cm, 99 cm and 123 cm.[19] The thick substrate and particularly careful polishing allowed a very precise optical surface, which is responsible for Chandra's unmatched resolution: between 80% and 95% of the incoming X-ray energy is focused into a one-arcsecond circle. However, the thickness of the substrates limit the proportion of the aperture which is filled, leading to the low collecting area compared to XMM-Newton.

Chandra's highly elliptical orbit allows it to observe continuously for up to 55 hours of its 65-hour orbital period. At its furthest orbital point from Earth, Chandra is one of the most distant Earth-orbiting satellites. This orbit takes it beyond the geostationary satellites and beyond the outer Van Allen belt.[20]

With an angular resolution of 0.5 arcsecond (2.4 µrad), Chandra possesses a resolution over 1000 times better than that of the first orbiting X-ray telescope.


The Science Instrument Module (SIM) holds the two focal plane instruments, the AXAF CCD Imaging Spectrometer (ACIS) and the High Resolution Camera (HRC), moving whichever is called for into position during an observation.

ACIS consists of 10 CCD chips and provides images as well as spectral information of the object observed. It operates in the photon energy range of 0.2–10 keV. HRC has two micro-channel plate components and images over the range of 0.1–10 keV. It also has a time resolution of 16 microseconds. Both of these instruments can be used on their own or in conjunction with one of the observatory's two transmission gratings.

The transmission gratings, which swing into the optical path behind the mirrors, provide Chandra with high resolution spectroscopy. The High Energy Transmission Grating Spectrometer (HETGS) works over 0.4–10 keV and has a spectral resolution of 60–1000. The Low Energy Transmission Grating Spectrometer (LETGS) has a range of 0.09–3 keV and a resolution of 40–2000.


Labeled diagram of CXO

See also


  1. 1 2 3 4 5 6 7 "Chandra Specifications". NASA/Harvard. Retrieved September 3, 2015.
  2. "Chandra X-Ray Observatory - Orbit". Heavens Above. September 3, 2015. Retrieved September 3, 2015.
  3. "The Chandra X-ray Observatory: Overview". Chandra X-ray Center. Retrieved September 3, 2015.
  4. Ridpath, Ian (2012). The Dictionary of Astronomy (2nd ed.). Oxford University Press. p. 82. ISBN 978-0-19-960905-5.
  5. 1 2 "And the co-winners are...". Harvard-Smithsonian Center for Astrophysics. 1998. Retrieved January 12, 2014.
  6. 1 2 Tucker, Wallace (October 31, 2013). "Tyrel Johnson & Jatila van der Veen - Winners of the Chandra-Naming Contest - Where Are They Now?". Harvard-Smithsonian Center for Astrophysics. Retrieved January 12, 2014.
  7. "Chandra's Mission Extended to 2009". Harvard-Smithsonian Center for Astrophysics. September 28, 2001.
  8. Schwartz, Daniel A. (August 2004). "The Development and Scientific Impact of the Chandra X-Ray Observatory". International Journal of Modern Physics D. 13 (7): 1239–1248. arXiv:astro-ph/0402275Freely accessible. Bibcode:2004IJMPD..13.1239S. doi:10.1142/S0218271804005377.
  9. "International X-ray Observatory".
  10. Howell, Elizabeth (November 1, 2013). "X-ray Space Telescope of the Future Could Launch in 2028". Retrieved January 1, 2014.
  11. "Students Using NASA and NSF Data Make Stellar Discovery; Win Science Team Competition" (Press release). NASA. December 12, 2000. Release 00-195. Retrieved April 15, 2013.
  12. Roy, Steve; Watzke, Megan (October 2006). "Chandra Reviews Black Hole Musical: Epic But Off-Key" (Press release). Harvard-Smithsonian Center for Astrophysics.
  13. Madejski, Greg (2005). Recent and Future Observations in the X-ray and Gamma-ray Bands: Chandra, Suzaku, GLAST, and NuSTAR. Astrophysical Sources of High Energy Particles and Radiation. June 20–24, 2005. Torun, Poland. AIP Conference Proceedings. 801. p. 21. arXiv:astro-ph/0512012Freely accessible. doi:10.1063/1.2141828.
  14. "Puzzling X-rays from Jupiter". March 7, 2002.
  15. Harrington, J. D.; Anderson, Janet; Edmonds, Peter (September 24, 2012). "NASA's Chandra Shows Milky Way is Surrounded by Halo of Hot Gas".
  16. "M60-UCD1: An Ultra-Compact Dwarf Galaxy". September 24, 2013.
  17. 1 2 Chou, Felicia; Anderson, Janet; Watzke, Megan (January 5, 2015). "RELEASE 15-001 - NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole". NASA. Retrieved January 6, 2015.
  18. "X-Ray Detection Sheds New Light on Pluto". Applied Physics Laboratory. September 14, 2016. Retrieved November 17, 2016.
  19. Gaetz, T. J.; Jerius, Diab (January 28, 2005). "The HRMA User's Guide" (PDF). Chandra X-ray Center. Archived from the original (PDF) on February 10, 2006.
  20. Gott, J. Richard; Juric, Mario (2006). "Logarithmic Map of the Universe". Princeton University.
  21. "Science Instruments". Harvard-Smithsonian Center for Astrophysics. Retrieved November 17, 2016.

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