A NASA satellite for X-ray astronomy, the third of NASA's series of four ‘Great Observatories’, launched by the space shuttle Columbia in July 1999. It carries a grazing-incidence X-ray telescope to observe X-rays of 0.1–10.0 keV energy from high-energy regions of the Universe such as the remnants of exploded stars, regions around black holes, ultra-hot gas in clusters of galaxies, active galactic nuclei, and quasars. The X-rays are studied by four instruments: the High Resolution Camera (HRC), the Advanced CCD Imaging Spectrometer (ACIS), High Energy Transmission Grating Spectrometer (HETGS), and the Low Energy Transmission Grating Spectrometer (LETGS).

Chandra operates from a highly elliptical orbit which takes it more than a third of the way to the Moon before returning to its closest approach to the Earth of 16 000 kilometres. It takes 64 hours and 18 minutes to complete an orbit, and uninterrupted observations up to 55 hours are possible.

The observatory is named after the Indian-born US astrophysicist Subrahmanyan Chandrasekhar, who won the 1983 Nobel Prize for Physics for his theoretical studies of the physical processes concerning the structure and evolution of stars.