View source for Great Observatories program

{{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.

== Origins of the Great Observatory program ==
The concept of a Great Observatory program was first proposed in the 1979 [[National Research Council (United States)|NRC]] report "A Strategy for Space Astronomy and Astrophysics for the 1980s".<ref name="NRC1979">{{cite book|url=https://nap.nationalacademies.org/catalog/12377/a-strategy-for-space-astronomy-and-astrophysics-for-the-1980s|title=A Strategy for Space Astronomy and Astrophysics for the 1980s|date=1979 |publisher=Washington, DC: The National Academies Press.|doi=10.17226/12377 |isbn=978-0-309-12341-9 }}</ref> This report laid the essential groundwork for the Great Observatories and was chaired by [[Peter Meyer (astrophysicist)|Peter Meyer]] (through June 1977) and then by [[Harlan James Smith|Harlan J. Smith]] (through publication). In the mid-1980s, it was further advanced by all of the astrophysics Division Directors at [[NASA Headquarters|NASA headquarters]], including Frank Martin and Charlie Pellerin. NASA's "Great Observatories" program used four separate satellites, each designed to cover a different part of the spectrum in ways which terrestrial systems could not. This perspective enabled the proposed X-ray and InfraRed observatories to be appropriately seen as a continuation of the astronomical program begun with Hubble and CGRO rather than competitors or replacements.<ref name="Stern">{{cite web|url=http://www-istp.gsfc.nasa.gov/stargaze/Sun6new.htm|title=Seeing the Sun in a New Light|access-date=2007-12-07|last=Stern |first=David P.|date=2004-12-12|work=From Stargazers to Starships|publisher=NASA Goddard Space Flight Center}} {{PD-notice}}</ref><ref>{{cite web|last=Roman|first=Nancy Grace|title=Exploring the Universe: Space-Based Astronomy and Astrophysics|work=Exploring the Cosmos|publisher=NASA|year=2001|url=http://science.hq.nasa.gov/missions/docs/Chap3-essay.PDF|archive-url=https://web.archive.org/web/20050527000717/http://science.hq.nasa.gov/missions/docs/Chap3-essay.PDF|url-status=dead|archive-date=2005-05-27|access-date=2007-12-08}} {{PD-notice}}</ref> Two explanatory documents published by NASA and created for the NASA Astrophysics Division and the NASA Astrophysics Management Working Group laid out the rationale for the suite of observatories and questions that could be addressed across the spectrum.<ref name="Harwit&Neal1986">{{cite web|url=https://ntrs.nasa.gov/api/citations/19860015241/downloads/19860015241.pdf|title=The Great Observatories for Space Astrophysics|last1=Harwit|first1=Martin|last2=Neal|first2=Valerie|date=1986-01-09|work=NASA document number 21M585|publisher=NASA}}</ref><ref name="Harwit&Neal1991">{{cite web|url=https://ntrs.nasa.gov/api/citations/19920001848/downloads/19920001848.pdf|title=The Great Observatories for Space Astrophysics|last1=Harwit|first1=Martin|last2=Neal|first2=Valerie|date=1991-01-01|work=NASA document number NP-128|publisher=NASA}}</ref> They had an important role in the campaign to win and sustain approval for the four telescopes.{{Citation needed|date=April 2024}}

== Great Observatories ==
=== Hubble Space Telescope ===
[[Image:Hubble Space Telescope (27946391011).jpg|thumb|Hubble Space Telescope]]

{{Main|Hubble Space Telescope}}

The history of the Hubble Space Telescope can be traced back to 1946, when the [[astronomer]] [[Lyman Spitzer]] wrote the paper ''Astronomical advantages of an extraterrestrial observatory''.<ref>Spitzer, L., ''REPORT TO PROJECT RAND: Astronomical Advantages of an Extra-Terrestrial Observatory'', reprinted in ''Astronomy Quarterly'' volume 7, p. 131, 1990</ref> Spitzer devoted much of his career to pushing for a space telescope.

The 1966–1972 [[Orbiting Astronomical Observatory]] missions demonstrated the important role space-based observations could play in astronomy. In 1968, NASA developed firm plans for a space-based [[reflecting telescope]] with a 3-meter mirror, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979.<ref>Spitzer, Lyman S (1979), "History of the Space Telescope", ''Quarterly Journal of the Royal Astronomical Society'', v. 20, p. 29</ref> Congress eventually approved funding of US$36 million for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983. During the early 1980s, the telescope was named after [[Edwin Hubble]].

Hubble was originally intended to be retrieved and returned to [[Earth]] by the [[Space Shuttle]], but the retrieval plan was later abandoned. On 31 October 2006, [[List of administrators and deputy administrators of NASA|NASA Administrator]] [[Michael D. Griffin]] gave the go-ahead for a final refurbishment mission. The 11-day [[STS-125]] mission by [[Space Shuttle Atlantis|Space Shuttle ''Atlantis'']], launched on 11 May 2009,<ref>{{cite web|url=http://www.nasa.gov/home/hqnews/2008/may/HQ_08133_Shuttle_target_dates.html|title=NASA Updates Space Shuttle Target Launch Dates|publisher=NASA|access-date=2008-05-22|archive-date=8 May 2017|archive-url=https://web.archive.org/web/20170508183104/https://www.nasa.gov/home/hqnews/2008/may/HQ_08133_Shuttle_target_dates.html|url-status=dead}}</ref> installed fresh batteries, replaced all gyroscopes, replaced a command computer, fixed several instruments, and installed the [[Wide Field Camera 3]] and the [[Cosmic Origins Spectrograph]].<ref name="Green Light">{{cite news|url=http://www.nbcnews.com/id/15489217|archive-url=https://web.archive.org/web/20131104010540/http://www.nbcnews.com/id/15489217/|url-status=dead|archive-date=4 November 2013|title=NASA gives green light to Hubble rescue|first=Alan|last=Boyle|publisher=NBC News|date=2006-10-31|access-date=2007-01-10}}</ref>

=== Compton Gamma Ray Observatory ===
[[File:CGRO s37-96-010.jpg|thumb|Compton Gamma Ray Observatory]]

{{Main|Compton Gamma Ray Observatory}}

Gamma rays had been examined above the atmosphere by several early space missions. During its [[HEAO Program|High Energy Astronomy Observatory Program]] in 1977, NASA announced plans to build a "great observatory" for [[gamma-ray astronomy]]. The Gamma Ray Observatory (GRO), renamed [[Compton Gamma-Ray Observatory]] (CGRO), was designed to take advantage of the major advances in detector technology during the 1980s. Following 14 years of effort, the CGRO was launched on 5 April 1991.<ref>{{cite web|url=http://heasarc.gsfc.nasa.gov/docs/cgro/epo/brochures/compton/bro5.html|title=Gamma-Ray Astronomy in the Compton Era: The Instruments|access-date=2007-12-07|work=Gamma-Ray Astronomy in the Compton Era|publisher=NASA (GSFC)| archive-url = https://web.archive.org/web/20090224125500/http://heasarc.gsfc.nasa.gov/docs/cgro/epo/brochures/compton/bro5.html | archive-date=2009-02-24| url-status=dead}} {{PD-notice}}</ref> One of the three [[gyroscope]]s on the Compton Gamma Ray Observatory failed in December 1999. Although the observatory was fully functional with two gyroscopes, NASA judged that failure of a second gyroscope would result in inability to control the satellite during its eventual return to Earth due to orbital decay. NASA chose instead to preemptively de-orbit Compton on 4 June 2000.<ref>{{cite web |url=https://spaceflightnow.com/cgrodeorbit/index.html|title=NASA space telescope heads for fiery crash into Pacific|first=William|last=Harwood|publisher=Spaceflight Now|access-date=2020-02-02}}</ref> Parts that survived reentry splashed into the [[Pacific Ocean]].

=== Chandra X-ray Observatory ===
[[File:Chandra_artist_illustration.jpg|thumb|Chandra X-ray Observatory]]

{{Main|Chandra X-ray Observatory}}

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 Observatory]] (HEAO-2), into orbit. Work continued on the Chandra project through 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.  Chandra'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 program|Space Shuttle]] but put the observatory above the Earth's [[Van Allen radiation belt|radiation belts]] for most of its orbit.

=== Spitzer Space Telescope ===
[[File:SIRTF_downlink.jpg|thumb|Spitzer points its high-gain antenna towards the Earth.]]

{{Main|Spitzer Space Telescope}}

By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of [[atmosphere of Earth]]. Most of the early concepts, envisioned repeated flights aboard the NASA Space Shuttle. This approach was developed in an era when the Shuttle program was presumed to be capable of supporting weekly flights of up to 30 days duration. In 1979, a National Research Council of the [[United States National Academy of Sciences|National Academy of Sciences]] report, ''A Strategy for Space Astronomy and Astrophysics for the 1980s'', identified a ''Shuttle Infrared Telescope Facility'' (SIRTF) as "one of two major astrophysics facilities [to be developed] for [[Spacelab]]," a Shuttle-borne platform.

The launch of the [[Infrared Astronomical Satellite]], an Explorer-class satellite designed to conduct the first [[infrared]] survey of the sky led to anticipation of an instrument using new infrared detector technology. By September 1983, NASA was considering the "possibility of a long duration [free-flyer] SIRTF mission". The 1985 [[STS-51-F|Spacelab-2]] flight aboard [[STS-51-F]] confirmed the Shuttle environment was not well suited to an onboard infrared telescope, and a free-flying design was better. The first word of the name was changed from ''Shuttle'' so it would be called the Space Infrared Telescope Facility.<ref>{{cite web|url=http://www.nasa.gov/mission_pages/spitzer/infrared/index.html|title=Studying the Universe in Infrared|access-date=2007-12-08|last=Watanabe|first=Susan|date=2007-11-22|publisher=NASA|archive-date=7 July 2019|archive-url=https://web.archive.org/web/20190707072050/https://www.nasa.gov/mission_pages/spitzer/infrared/index.html|url-status=dead}} {{PD-notice}}</ref><ref>{{cite web|last=Kwok|first=Johnny|title=Finding a Way: The Spitzer Space Telescope Story|work=Academy Sharing Knowledge|publisher=NASA|date=Fall 2006 |url=http://appel.nasa.gov/ask/issues/25/25s_finding.php|access-date =2007-12-09|url-status=dead|archive-url=https://web.archive.org/web/20070908000438/http://appel.nasa.gov/ask/issues/25/25s_finding.php|archive-date=2007-09-08}} {{PD-notice}}</ref>

Spitzer was the only one of the Great Observatories not launched by the Space Shuttle. It was originally intended to be so launched, but after the [[STS-51L|''Challenger'' disaster]], the [[Centaur (rocket stage)|Centaur]] [[Liquid hydrogen|LH2]]/[[Liquid oxygen|LOX]] [[Multistage rocket|upper stage]] that would have been required to push it into a [[heliocentric orbit]] was banned from Shuttle use. [[Titan (rocket family)|Titan]] and [[Atlas (rocket family)|Atlas]] launch vehicles were canceled for cost reasons. After redesign and lightening, it was launched in 2003 by a [[Delta II]] [[launch vehicle]] instead. It was called the [[Spitzer Space Telescope|Space Infrared Telescope Facility]] (SIRTF) before launch. The telescope was deactivated when operations ended on 30 January 2020.

== Timeline ==
{{NASA Great Observatories Program}}

== Strengths ==
[[File:Crab Nebula NGC 1952 (composite from Chandra, Hubble and Spitzer).jpg|thumb|upright=1.0|right|Chandra, Hubble, and Spitzer composite image of the [[Crab Nebula]] (2009)]]

Since the Earth's atmosphere prevents [[X-ray astronomy|X-rays]], [[gamma-ray astronomy|gamma-rays]]<ref>Note: Gamma-rays from space can be detected indirectly from the ground by a technique known as [[IACT|Imaging Air Cherenkov Technique]] or IACT for short. It was pioneered by the [[Fred Lawrence Whipple Observatory|Whipple Observatory]] in 1968 and several newer telescopes have been built in various countries since then.</ref> and [[far infrared astronomy|far-infrared]] [[radiation]] from reaching the ground, space missions were essential for the Compton, Chandra and Spitzer observatories. Hubble also benefits from being above the atmosphere, as the atmosphere blurs ground-based observations of very faint objects, decreasing spatial resolution (however brighter objects can be imaged in much higher resolution than by Hubble from the ground using [[astronomical interferometer]]s or [[adaptive optics]]). Larger, ground-based telescopes have only recently matched Hubble in resolution for near-infrared wavelengths of faint objects. Being above the atmosphere eliminates the problem of [[airglow]], allowing Hubble to make observations of ultrafaint objects. Ground-based telescopes cannot compensate for airglow on ultrafaint objects, and so very faint objects require unwieldy and inefficient exposure times. Hubble can also observe at [[ultraviolet]] wavelengths which do not penetrate the atmosphere.

Each observatory was designed to push the state of technology in its region of the electromagnetic spectrum. Compton was much larger than any gamma-ray instruments flown on the previous [[HEAO Program|HEAO]] missions, opening entirely new areas of observation. It had four instruments covering the 20 [[keV]] to 30 [[GeV]] energy range, which complemented each other's sensitivities, resolutions, and fields of view. Gamma rays are emitted by various high-energy and high-temperature sources, such as [[black hole]]s, [[pulsar]]s, and [[supernovae]].

Chandra similarly had no ground predecessors. It followed the three NASA [[HEAO Program]] satellites, notably the highly successful [[Einstein Observatory]], which was the first to demonstrate the power of [[Wolter telescope|grazing-incidence, focusing X-ray optics]], giving spatial resolution an order of magnitude better than [[collimator|collimated]] instruments (comparable to optical telescopes), with an enormous improvement in sensitivity. Chandra's large size, high orbit, and sensitive [[Charge-coupled device|CCDs]] allowed observations of very faint X-ray sources.

Spitzer also observes at wavelength largely inaccessible to ground telescopes. It was preceded in space by NASA's smaller [[IRAS]] mission and [[European Space Agency]] (ESA)'s large [[Infrared Space Observatory|ISO]] telescope. Spitzer's instruments took advantage of the rapid advances in infrared detector technology since IRAS, combined with its large aperture, favorable fields of view, and long life. Science returns were accordingly outstanding.{{Citation needed|date=April 2024}} Infrared observations are necessary for very distant astronomical objects where all the visible light is [[redshift]]ed to infrared wavelengths, for cool objects which emit little visible light, and for regions optically obscured by dust.

== Synergies ==
[[File:Ssc2004-15b.jpg|thumb|upright=1.0|right|A labeled space image comparing views of a supernova remnant by three different Great observatories.]]

Aside from inherent mission capabilities (particularly sensitivities, which cannot be replicated by ground observatories), the Great Observatories program allows missions to interact for greater science return.  Different objects shine in different wavelengths, but training two or more observatories on an object allows a deeper understanding.

High-energy studies (in X-rays and gamma rays) have had only moderate imaging resolutions so far. Studying X-ray and gamma-ray objects with Hubble, as well as Chandra and Compton, gives accurate size and positional data. In particular, Hubble's resolution can often discern whether the target is a standalone object, or part of a parent galaxy, and if a bright object is in the nucleus, arms, or halo of a [[spiral galaxy]]. Similarly, the smaller aperture of Spitzer means that Hubble can add finer spatial information to a Spitzer image. Reported in March 2016, Spitzer and Hubble were used to discover the most distant-known galaxy, [[GN-z11]]. This object was seen as it appeared 13.4 billion years ago.<ref name="spitzer20160303">{{cite web |url=http://www.spitzer.caltech.edu/news/1861-feature16-04-Hubble-Team-Breaks-Cosmic-Distance-Record|title=Hubble Team Breaks Cosmic Distance Record|series=Spitzer Space Telescope|publisher=NASA|date=3 March 2016|access-date=14 December 2016}} {{PD-notice}}</ref><ref name="nasa20160825">{{cite web|url=http://www.jpl.nasa.gov/news/news.php?feature=6602|title=Spitzer Space Telescope Begins "Beyond" Phase |publisher=NASA|first=Elizabeth|last=Landau|date=25 August 2016|access-date=9 December 2016}} {{PD-notice}}</ref> ([[List of the most distant astronomical objects]])

Ultraviolet studies with Hubble also reveal the temporal states of high-energy objects. X-rays and gamma rays are harder to detect with current technologies than visible and ultraviolet. Therefore, Chandra and Compton needed long integration times to gather enough photons. However, objects which shine in X-rays and gamma rays can be small, and can vary on timescales of minutes or seconds. Such objects then call for followup with Hubble or the [[Rossi X-ray Timing Explorer]], which can measure details in angular seconds or fractions of a second, due to different designs. Rossi's last full year of operation was 2011.

The ability of Spitzer to see through dust and thick gases is good for galactic nuclei observations. Massive objects at the hearts of galaxies shine in X-rays, gamma rays, and radio waves, but infrared studies into these clouded regions can reveal the number and positions of objects.

Hubble, meanwhile, has neither the [[field of view]] nor the available time to study all interesting objects. Worthwhile targets are often found with ground telescopes, which are cheaper, or with smaller space observatories, which are sometimes expressly designed to cover large areas of the sky. Also, the other three Great Observatories have found interesting new objects, which merit diversion of Hubble.

One example of observatory synergy is [[Solar System]] and [[asteroid]] studies. Small bodies, such as small [[Natural satellite|moons]] and asteroids, are too small and/or distant to be directly resolved even by Hubble; their image appears as a [[diffraction]] pattern determined by brightness, not size. However, the minimum size can be deduced by Hubble through knowledge of the body's [[albedo]]. The maximum size can be determined by Spitzer through knowledge of the body's temperature, which is largely known from its orbit. Thus, the body's true size is bracketed. Further [[spectroscopy]] by Spitzer can determine the chemical composition of the object's surface, which limits its possible albedos, and therefore sharpens the low size estimate.

At the opposite end of the [[cosmic distance ladder]], observations made with Hubble, Spitzer and Chandra have been combined in the [[Great Observatories Origins Deep Survey]] to yield a multi-wavelength picture of [[galaxy formation and evolution]] in the early [[Universe]].

{{wide image|File:Center of the Milky Way Galaxy IV – Composite.jpg|1000px|[[Milky Way]] [[Galactic Center]] as seen by  the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory}}

== Impact ==
All four telescopes have had a substantial impact on astronomy. The opening up of new wavebands to high resolution, high sensitivity observations by the Compton, Chandra and Spitzer has revolutionized our understanding of a wide range of astronomical objects, and has led to the detection of thousands of new, interesting objects. Hubble has had a much larger public and media impact than the other telescopes,  although at optical wavelengths Hubble has provided a more modest improvement in sensitivity and resolution over existing instruments. Hubble's capability for uniform high-quality imaging of any astronomical object at any time has allowed accurate surveys and comparisons of large numbers of astronomical objects. The [[Hubble Deep Field]] observations have been very important for studies of distant galaxies, as they provide rest-frame ultraviolet images of these objects with a similar number of pixels across the galaxies as previous ultraviolet images of closer galaxies, allowing direct comparison.

== Successors to Great Observatories ==
[[File:Telescope Primary Mirror Sizes Compared (4198-Image).png|thumb|Primary mirror size comparison of Spitzer, Hubble, and [[James Webb Space Telescope|Webb]] telescopes]]

* The [[James Webb Space Telescope]] (JWST) launched in December 2021 and works simultaneously with Hubble.<ref>{{cite web|url=https://jwst.nasa.gov/about.html|title=About the James Webb Space Telescope|work=Goddard Space Flight Center|publisher=NASA|access-date=2018-12-20}} {{PD-notice}}</ref> Its segmented, deployable mirror is over twice as wide as the Hubble's, increasing angular resolution noticeably, and sensitivity dramatically. Unlike Hubble, JWST observes in the infrared, in order to penetrate dust at cosmological distances. This means it continues some Spitzer capabilities, while some Hubble capabilities are lost in the visible and especially the ultraviolet wavelengths. JWST exceeds Spitzer's performance in near-infrared. The [[European Space Agency|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 observed in near- and mid-infrared. SOFIA had a larger aperture than Spitzer, but lower relative sensitivity.
* The [[Fermi Gamma-ray Space Telescope]] (FGRST), formerly known as the Gamma Ray Large Area Space Telescope, is a follow-on to Compton launched on 11 June 2008.<ref>{{cite web |url=http://www.nasa.gov/missions/highlights/schedule.html|title=NASA's Shuttle and Rocket Missions — Launch Schedule|publisher=NASA|date=2008-06-05}} {{PD-notice}}</ref> FGRST is more narrowly defined, and much smaller; it carries only one main instrument and a secondary experiment, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). FGRST is complemented by [[Swift Gamma-Ray Burst Mission|Swift]], launched in 2004, and previously by [[HETE 2|HETE-2]], launched in 2000. 
* The [[Reuven Ramaty High Energy Solar Spectroscopic Imager]] (RHESSI), observed in some Compton and Chandra wavelengths between its February 2002 launch and April 2023 decommissioning. RHESSI was pointed at the [[Sun]] at all times, but it occasionally observed high-energy objects in its peripheral view.
*  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.

== Later programs ==
* The [[Beyond Einstein program]] will seek to develop new areas of science. [[Constellation-X]] and the [[Laser Interferometer Space Antenna]] (LISA) have been referred to by NASA as the [[Einstein Great Observatories]], to differentiate them from the current generation. However, they are not a part of the Great Observatories program.<ref>{{cite web|title=Great Observatories|work=Beyond Einstein|publisher=NASA
|url=http://universe.nasa.gov/program/observatories.html|access-date=2007-11-28|url-status=dead|archive-url=https://web.archive.org/web/20071103084630/http://universe.nasa.gov/program/observatories.html|archive-date=2007-11-03}} {{PD-notice}}</ref>

* The [[International Solar-Terrestrial Physics Science Initiative]] (ISTP), in the spirit of the Great Observatories program, is a group of instruments to study the Sun and related electromagnetic phenomena near Earth.<ref>{{cite web|url=http://pwg.gsfc.nasa.gov/istp/admin/proposal/1-1.html|title=The GGS Program|access-date=2007-12-03|last=Acuña|first=Mario H.|author2=Keith W. Ogilvie|author3=Robert A. Hoffman |author4=Donald H. Fairfield|author5=Steven A. Curtis|author6=James L. Green|author7=William H. Mish|author8=the GGS Science Teams|date=1997-05-01|work=ISTP-GGS/SOLARMAX Proposal|publisher=Goddard Space Flight Center}} {{PD-notice}}</ref>

== Next Great Observatory ==
In 2016, [[NASA]] began considering four different [[Large strategic science missions|Flagship]] [[space telescope]]s,<ref name="Sci.Am. 2016"/> they are the [[Habitable Exoplanet Imaging Mission]] (HabEx), [[Large UV Optical Infrared Surveyor]] (LUVOIR), [[Origins Space Telescope]] (OST), and [[Lynx X-ray Observatory]]. In 2019, the four teams will turn their final reports over to the [[National Academy of Sciences]], whose independent [[Astronomy and Astrophysics Decadal Survey|Decadal Survey]] committee advises NASA on which mission should take top priority.<ref name="Sci.Am. 2016">{{cite news|last=Scoles|first=Sarah|url=https://www.scientificamerican.com/article/nasa-considers-its-next-flagship-space-telescope/#|title=NASA Considers Its Next Flagship Space Telescope|work=Scientific American|date=30 March 2016|access-date=2017-10-15}}</ref>

[[NASA]] announced the [[Habitable Worlds Observatory]] (HWO) in 2023, a successor building on the [[Large UV Optical Infrared Surveyor]] (LUVOIR) and [[Habitable Exoplanet Imaging Mission]] (HabEX) proposals.<ref>{{cite web|url=https://science.nasa.gov/astrophysics/programs/habitable-worlds-observatory//|title=Habitable Worlds Observatory|access-date=2024-06-04|publisher=NASA}}</ref> The administration also created the [[Habitable Worlds Observatory#Development|Great Observatory Maturation Program]] for the development of the [[Habitable Worlds Observatory]].<ref>{{cite web|url=https://science.nasa.gov/astrophysics/programs/habitable-worlds-observatory/gomap/|title=Great Observatory Maturation Program|access-date=2024-06-04|publisher=NASA}}</ref>

== See also ==
{{Portal|Spaceflight}}
* [[Beyond Einstein program]]
* [[Herschel Space Telescope]] (Far infrared space observatory, 2009–2013)
* [[List of space telescopes]]

== Notes and references ==
{{Reflist|30em}}

== Further reading ==
* {{cite arXiv |last1=Armus |first1=L. |last2=Megeath |first2=S. T. |last3=Corrales |first3=L. |last4=Marengo |first4=M. |last5=Kirkpatrick |first5=A. |last6=Smith |first6=J. D. |last7=Meyer |first7=M. |last8=Gezari |first8=S. |last9=Kraft |first9=R. P. |last10=McCandliss |first10=S. |last11=Tuttle |first11=S. |last12=Elvis |first12=M. |last13=Bentz |first13=M. |last14=Binder |first14=B. |last15=Civano |first15=F. |last16=Dragomir |first16=D. |last17=Espaillat |first17=C. |last18=Finkelstein |first18=S. |last19=Fox |first19=D. B. |last20=Greenhouse |first20=M. |last21=Hamden |first21=E. |last22=Kauffmann |first22=J. |last23=Khullar |first23=G. |last24=Lazio |first24=J. |last25=Lee |first25=J. |last26=Lillie |first26=C. |last27=Lightsey |first27=P. |last28=Mushotzky |first28=R. |last29=Scarlata |first29=C. |last30=Scowen |first30=P. |last31=Tremblay |first31=G. R. |last32=Wang |first32=Q. D. |last33=Wolk |first33=S. |title=Great Observatories: The Past and Future of Panchromatic Astrophysics |date=2021 |class=astro-ph.IM |eprint=2104.00023 |display-authors=1}}

== External links ==
* {{cite web|title=Preflight Videos (STS-93)|publisher=NASA|date=9 April 2002|url=http://spaceflight1.nasa.gov/gallery/video/shuttle/sts-93/html/fd0.html|quote=A detailed description of NASA's Great Observatories, including STS-93 primary payload, the Chandra X-ray Observatory |access-date=2007-11-27|url-status=dead|archive-url=https://web.archive.org/web/20071209094039/http://spaceflight1.nasa.gov/gallery/video/shuttle/sts-93/html/fd0.html|archive-date=9 December 2007}}
* [http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/hst_sm4/index.html STS-125: Final Shuttle Mission to Hubble Space Telescope] {{Webarchive|url=https://web.archive.org/web/20150716065546/http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/hst_sm4/index.html |date=16 July 2015 }}
* [https://web.archive.org/web/20140912044304/http://www.worldwidetelescope.org/Interact/GreatObservatories Great Observatories Interactive using WorldWide Telescope]

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[[Category:Great Observatories program| ]]
[[Category:Space telescopes]]
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