Editing Great Observatories program (section)

{{short description|Series of NASA satellites}}
{{Use American English|date=March 2021}}
{{Use dmy dates|date=March 2021}}
[[File:Great Observatories.jpg|thumb|upright=1.3|right|Four Great Observatories]]

[[NASA]]'s series of '''Great Observatories''' [[satellite]]s are four large, powerful [[space telescope|space-based astronomical telescopes]] launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the [[electromagnetic spectrum]]: [[gamma ray]]s, [[X-ray]]s, [[Visible light|visible]] and [[ultraviolet light]], and [[Infrared|infrared light]].

The [[Hubble Space Telescope]] (HST) primarily observes [[optical spectrum|visible light]] and [[Near ultraviolet|near-ultraviolet]]. It was launched in 1990 aboard the [[Space Shuttle Discovery|Space Shuttle ''Discovery'']] during [[STS-31]], but its main mirror had been ground incorrectly, resulting in [[spherical aberration]] that compromised the telescope's capabilities. The optics were corrected to their intended quality by the [[STS-61]] servicing mission in 1993. In 1997, the [[STS-82]] servicing mission added capability in the [[Near infrared|near-infrared]] range, and in 2009 the [[STS-125]] servicing mission refurbished the telescope and extended its projected service life. It remains in active operation {{as of|2024|10|lc=y}}.

The [[Compton Gamma Ray Observatory]] (CGRO) primarily observed [[gamma ray]]s, though it extended into [[hard x-ray]]s as well. It was launched in 1991 aboard ''[[Space Shuttle Atlantis|Atlantis]]'' during [[STS-37]]. It was [[Atmospheric entry|de-orbited]] in 2000 after a gyroscope failed.

The [[Chandra X-ray Observatory]] (CXO) primarily observes [[soft X-ray]]s. It was launched in 1999 aboard ''[[Space Shuttle Columbia|Columbia]]'' during [[STS-93]] into an elliptical high-Earth orbit, and was initially named the Advanced X-ray Astronomical Facility (AXAF). It remains in active operation {{as of|2024|10|lc=y}}.

The [[Spitzer Space Telescope]] (SST) observed the [[infrared]] spectrum. It was launched in 2003 aboard a [[Delta II rocket]] into an Earth-trailing solar orbit. Depletion of its [[liquid helium]] coolant in 2009 reduced its functionality, leaving it with only two short-wavelength imaging modules. It was removed from service and placed into safe-mode on January 30, 2020.