Editing Chandra X-ray Observatory (section)

==Technical description==
[[File:Chandra X-ray space observatory Obs assemb2 300.jpg|thumb|Assembly of the telescope]]
[[File:Chandra telescope mirror assembled Hrma7 300.jpg|thumb|The main mirror of AXAF (Chandra)]]
[[File:Chandra X-ray space observatory - HRCfront-150.jpg|thumb|HRC flight unit of Chandra]]

Unlike [[optical]] telescopes which possess simple aluminized [[Parabolic reflector|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 [[photon]]s 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&nbsp;cm-thick glass, with the reflecting surface a 33&nbsp;nm iridium coating, and the diameters are 65&nbsp;cm, 87&nbsp;cm, 99&nbsp;cm and 123&nbsp;cm.<ref>{{cite web |url=http://cxc.harvard.edu/cal/Hrma/users_guide/hrma-notes.pdf |title=The HRMA User's Guide |publisher=Chandra X-ray Center |first1=T. J. |last1=Gaetz |first2=Diab |last2=Jerius |date=January 28, 2005 |archive-url=https://web.archive.org/web/20060210070532/http://cxc.harvard.edu/cal/Hrma/users_guide/hrma-notes.pdf |archive-date=February 10, 2006}}</ref> 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 substrate limits the proportion of the aperture which is filled, leading to the low collecting area compared to [[XMM-Newton]].

Chandra's highly [[ellipse|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]].<ref>{{cite web |last1=Gott |first1=J. Richard |last2=Juric |first2=Mario |date=2006 |url=http://www.astro.princeton.edu/universe/ |title=Logarithmic Map of the Universe |publisher=Princeton University }}</ref>

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.

CXO uses mechanical [[gyroscope]]s,<ref>{{cite web |url=http://jwst.nasa.gov/faq_scientists.html |title=Technical Frequently Asked Questions (FAQ) |series=James Webb Space Telescope |publisher=NASA |access-date=December 14, 2016 }}</ref> which are sensors that help determine what direction the telescope is pointed.<ref name="chandra-spacecraft">{{cite web |url=http://chandra.harvard.edu/about/spacecraft.html |title=Spacecraft: Motion, Heat, and Energy |series=Chandra X-ray Observatory |publisher=NASA |date=March 17, 2014 |access-date=December 14, 2016 }}</ref> Other navigation and orientation systems on board CXO include an aspect camera, Earth and [[Sun sensor]]s, and [[reaction wheel]]s. It also has two sets of thrusters, one for movement and another for offloading momentum.<ref name="chandra-spacecraft" />