page_title: Great Observatories program
section_title: Successors to GO instruments
hierarchical_section_title: Great Observatories program / Successors to GO instruments
caption_attribution_description: English: International X-ray Observatory side view, artist's impression.
context_page_description: NASA's series of Great Observatories satellites are four large, powerful 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 rays, X-rays, visible and ultraviolet light, and infrared light. Two remain operational as of 2020.
context_section_description: James Webb Space Telescope (JWST) — the JWST, previously known as the NGST (Next Generation Space Telescope) is projected to launch in October 2021, and will work simultaneously with Hubble until its mission ends and the JWST replaces it.  Its segmented, deployable mirror will be over twice as wide, increasing angular resolution noticeably, and sensitivity dramatically.  Unlike Hubble, JWST will observe in the infrared, in order to penetrate dust at cosmological distances.  This means it will continue some Spitzer capabilities, while some Hubble capabilities will be lost in the visible and especially the ultraviolet wavelengths.
  The Fermi Gamma-ray Space Telescope, formerly GLAST, the Gamma Ray Large Area Space Telescope, is a follow-on to Compton launched on June 11, 2008. GLAST is more narrowly defined, and much smaller; it will carry only one main instrument and a secondary experiment. Other missions, such as HETE-2, launched in 2000, and Swift, launched in 2004, will complement GLAST. The Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), launched in 2002, observes in some Compton and Chandra wavelengths, but is pointed at the Sun at all times. Occasionally it observes high-energy objects which happen to be in the view around the Sun.
  Another large, high-energy observatory is INTEGRAL, Europe's INTErnational Gamma Ray Astrophysics Laboratory, launched in 2002.  It observes in similar frequencies to Compton. INTEGRAL uses a fundamentally different telescope technology, coded-aperture masks. Thus, its capabilities are complementary to Compton and Fermi.
  JWST will exceed Spitzer's performance in near-infrared, and the European Space Agency's Herschel Space Observatory, operational from 2009 to 2013, has exceeded Spitzer in the far-infrared. The SOFIA (Stratospheric Observatory For Infrared Astronomy) airborne platform observes in near- and mid-infrared. SOFIA has a larger aperture than Spitzer, but lower relative sensitivity.
caption: IXO was considered as a possible future X-ray observatory
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