<Tr> <Td_colspan="2"> Great Observatories ← Compton Spitzer → </Td> </Tr> <P> 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 2018 . </P> <P> 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 the Nobel Prize - winning Indian - American astrophysicist Subrahmanyan Chandrasekhar . Its mission is similar to that of ESA's XMM - Newton spacecraft, also launched in 1999 . </P> <P> 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 . </P>

Who is nasa's chandra xray observatory named after