NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

's series of Great Observatories

satellite A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...

s are four large, powerful space-based astronomical

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...

s launched between 1990 and 2003. They were built with different technology to examine specific wavelength/energy regions of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...

gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

s, visible and

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

, and

infrared light Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from arou ...

. * The

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

(HST) primarily observes

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

and

near-ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

. It was launched in 1990 aboard the Space Shuttle ''Discovery'' during STS-31. In 1997 the

STS-82 STS-82 was the 22nd flight of the Space Shuttle ''Discovery'' and the 82nd mission of the Space Shuttle program. It was NASA's second mission to service the Hubble Space Telescope, during which ''Discovery's'' crew repaired and upgraded the tel ...

servicing mission added capability in the

near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...

range, and in 2009 the

STS-125 STS-125, or HST-SM4 (Hubble Space Telescope Servicing Mission 4), was the fifth and final Space Shuttle mission to the Hubble Space Telescope (HST) and the last solo flight of the Space Shuttle ''Atlantis''. The launch of the Space Shuttle ''Atl ...

mission fixed the telescope and extended its projected service life. * The

Compton Gamma Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with photon energy, energies from 20 kElectronvolt#Properties, eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main tele ...

(CGRO) primarily observed

s, though it extended into

hard x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&n ...

s as well. It was launched in 1991 aboard ''

Atlantis Atlantis ( grc, Ἀτλαντὶς νῆσος, , island of Atlas) is a fictional island mentioned in an allegory on the hubris of nations in Plato's works '' Timaeus'' and '' Critias'', wherein it represents the antagonist naval power that b ...

'' during

STS-37 STS-37, the thirty-ninth NASA Space Shuttle mission and the eighth flight of the Space Shuttle ''Atlantis'', was a six-day mission with the primary objective of launching the Compton Gamma Ray Observatory (CGRO), the second of the Great Observ ...

and was

de-orbit Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: ''uncontrolled entry'', such as the entr ...

ed in 2000 after a gyroscope failed. * The

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources 1 ...

(CXO) primarily observes

soft X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30 ...

s. It was launched in 1999 aboard '' Columbia'' during

STS-93 STS-93 in 1999 marked the 95th launch of the Space Shuttle, the 26th launch of ''Columbia'', and the 21st night launch of a Space Shuttle. Eileen Collins became the first female shuttle Commander on this flight. Its primary payload was the Chan ...

into an elliptical high-Earth orbit, and was initially named the Advanced X-ray Astronomical Facility (AXAF). * The Spitzer Space Telescope (SST) observed the

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

spectrum. It was launched in 2003 aboard a Delta II rocket into an Earth-trailing solar orbit. Depletion of its

liquid helium Liquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures. Liquid helium may show superfluidity. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temp ...

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.

Great Observatories

The Hubble Space Telescope and Chandra X-ray Observatory continue to operate as of April 2022. Hubble was originally intended to be retrieved and returned to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

by the

Space Shuttle The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program ...

, but the retrieval plan was later abandoned. On 31 October 2006,

NASA Administrator The Administrator of the National Aeronautics and Space Administration is the highest-ranking official of NASA, the national space agency of the United States. The administrator is NASA's chief decision maker, responsible for providing clarity to ...

Michael D. Griffin Michael Douglas Griffin (born November 1, 1949) is an American physicist and aerospace engineer who served as the Under Secretary of Defense for Research and Engineering from 2018 to 2020. He previously served as Deputy of Technology for the Str ...

gave the go-ahead for a final refurbishment mission. The 11-day

mission by Space Shuttle ''Atlantis'', launched on 11 May 2009, installed fresh batteries, replaced all gyroscopes, replaced a command computer, fixed several instruments, and installed the

Wide Field Camera 3 The Wide Field Camera 3 (WFC3) is the Hubble Space Telescope's last and most technologically advanced instrument to take images in the visible spectrum. It was installed as a replacement for the Wide Field and Planetary Camera 2 during the first ...

and the

Cosmic Origins Spectrograph The Cosmic Origins Spectrograph (COS) is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 ( STS-125) in May 2009. It is designed for ultraviolet (90–320 nm) spectroscopy of faint point sources ...

. One of the three gyroscopes 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. Parts that survived reentry splashed into the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

. 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 ''Challenger'' disaster, the Centaur LH2/

LOX Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries—is the liquid form of molecular oxygen. It was used as the oxidizer in the first liquid-fueled rocket invented in 1926 by Robert H. Goddard, an appli ...

upper stage A multistage rocket or step rocket is a launch vehicle that uses two or more rocket ''stages'', each of which contains its own engines and propellant. A ''tandem'' or ''serial'' stage is mounted on top of another stage; a ''parallel'' stage is ...

that would have been required to push it into a heliocentric orbit was banned from Shuttle use. Titan and

Atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...

launch vehicles were canceled for cost reasons. After redesign and lightening, it was launched by a

Delta II Delta II was an expendable launch system, originally designed and built by McDonnell Douglas. Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 ...

launch vehicle A launch vehicle or carrier rocket is a rocket designed to carry a payload ( spacecraft or satellites) from the Earth's surface to outer space. Most launch vehicles operate from a launch pads, supported by a launch control center and ...

instead. It was called the Space Infrared Telescope Facility (SIRTF) before launch.

History of the program

Hubble Space Telescope

The history of the Hubble Space Telescope can be traced back to 1946, when the

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

Lyman Spitzer Lyman Spitzer Jr. (June 26, 1914 – March 31, 1997) was an American theoretical physicist, astronomer and mountaineer. As a scientist, he carried out research into star formation, plasma physics, and in 1946, conceived the idea of telesco ...

wrote the paper ''Astronomical advantages of an extraterrestrial observatory''. Spitzer devoted much of his career to pushing for a space telescope. The 1966–1972

Orbiting Astronomical Observatory The Orbiting Astronomical Observatory (OAO) satellites were a series of four American space observatories launched by NASA between 1966 and 1972, managed by NASA Chief of Astronomy Nancy Grace Roman. These observatories, including the first su ...

missions demonstrated the important role space-based observations could play in astronomy. In 1968, NASA developed firm plans for a space-based

reflecting telescope A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...

with a 3-meter mirror, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979. 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.

Gamma ray program

Gamma rays had been examined above the atmosphere by several early space missions. During its High Energy Astronomy Observatory Program in 1977, NASA announced plans to build a "great observatory" for

gamma-ray astronomy Gamma-ray astronomy is the astronomical observation of gamma rays,Astronomical literature generally hyphenates "gamma-ray" when used as an adjective, but uses "gamma ray" without a hyphen for the noun. the most energetic form of electromagneti ...

. The Gamma Ray Observatory (GRO), renamed

Compton Gamma-Ray Observatory The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with energies from 20 k eV to 30 GeV, in Earth orbit from 1991 to 2000. The observatory featured four main telescopes in one spacecraft, covering X-ra ...

(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.

Chandra X-ray Observatory history

In 1976 the

(called AXAF at the time) was proposed to NASA by

Riccardo Giacconi Riccardo Giacconi ( , ; October 6, 1931 – December 9, 2018) was an Italian-American Nobel Prize-winning astrophysicist who laid down the foundations of X-ray astronomy. He was a professor at the Johns Hopkins University. Biography Born in ...

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 Einstein Observatory (HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert E ...

(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

but put the observatory above the Earth's radiation belts for most of its orbit.

Spitzer history

By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of

atmosphere of Earth The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...

. 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 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 o be developedfor

Spacelab Spacelab was a reusable laboratory developed by European Space Agency (ESA) and used on certain spaceflights flown by the Space Shuttle. The laboratory comprised multiple components, including a pressurized module, an unpressurized carrier, ...

," a Shuttle-borne platform. The launch of the

Infrared Astronomical Satellite The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mon ...

, an Explorer-class satellite designed to conduct the first

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 ree-flyerSIRTF mission". The 1985 Spacelab-2 flight aboard

STS-51-F STS-51-F (also known as Spacelab 2) was the 19th flight of NASA's Space Shuttle program and the eighth flight of Space Shuttle ''Challenger''. It launched from Kennedy Space Center, Florida, on July 29, 1985, and landed eight days later on Aug ...

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.

Great Observatory origin

The concept of a Great Observatory program was first proposed in the 1979 NRC report "A Strategy for Space Astronomy and Astrophysics for the 1980s". This report laid the essential groundwork for the Great Observatories and was chaired by Peter Meyer (through June 1977) and then by 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, officially known as Mary W. Jackson NASA Headquarters or NASA HQ and formerly named Two Independence Square, is a low-rise office building in the two-building Independence Square complex at 300 E Street SW in Washington, D.C. ...

, 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. [Another citation for this paragraph should be two explanatory documents published by NASA and created for the NASA Astrophysics Division, then led by Charie Pellerin, and the NASA Astrophysics Management Working Group in the 1980s. Both are titled ''The Great Observatories for Space Astrophysics''; the first bears NASA document number 21M585 and the second is NP-128. Now hard to find, they laid out the rationale for the suite of observatories and questions that could be addressed across the spectrum. They had an important role in the campaign to win and sustain approval for the four telescopes. Co-authors were astrophysicist Martin Harwit and writer Valerie Neal, working in collaboration with a larger group of scientists in the mentioned Working Group.]

Strengths

Each observatory was designed to push the state of technology in its intended wavelength region. Since the Earth's atmosphere prevents X-ray astronomy, X-rays,

gamma-rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

and

far-infrared Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20 THz to ...

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 interferometers or

adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...

). 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 Airglow (also called nightglow) is a faint emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky never to be completely dark, even after the effects of starlight and diffu ...

, 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 Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...

wavelengths which do not penetrate the atmosphere. Compton observed in gamma rays, which do not penetrate the lower atmosphere. It was much larger than any gamma-ray instruments flown on the previous HEAO missions, opening entirely new areas of observation. It had four instruments covering the 20

keV Kev can refer to: Given name * Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991 * Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter * Kev Coghlan (born 1988), Scottish Grand Prix moto ...

to 30

GeV GEV may refer to: * ''G.E.V.'' (board game), a tabletop game by Steve Jackson Games * Ashe County Airport, in North Carolina, United States * Gällivare Lapland Airport, in Sweden * Generalized extreme value distribution * Gev Sella, Israeli-Sou ...

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 holes, pulsars, and supernovae. Chandra similarly had no ground predecessors. It followed the three NASA

HEAO Program The High Energy Astronomy Observatory Program was a NASA program of the late 1970s and early 1980s that included a series of three large low-Earth-orbiting spacecraft for X-ray and Gamma-Ray astronomy and Cosmic-Ray investigations. After launch, th ...

satellites, notably the highly successful

, which was the first to demonstrate the power of grazing-incidence, focusing X-ray optics, giving spatial resolution an order of magnitude better than

collimated A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...

instruments (comparable to optical telescopes), with an enormous improvement in sensitivity. Chandra's large size, high orbit, and sensitive 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 The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mo ...

mission and European Space Agency (ESA)'s large

ISO ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * 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 have been accordingly outstanding. Infrared observations are necessary for very distant astronomical objects where all the visible light is redshifted to infrared wavelengths, for cool objects which emit little visible light, and for regions optically obscured by dust.

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 The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area about 2.6 arcminutes on a side, about one 24-millionth of the ...

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. The James Webb Space Telescope will provide an even greater step forward, providing rest-frame visible light images of even more distant galaxies which can be directly compared with images of nearby galaxies at visible light wavelengths.

Synergies

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. 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 The Rossi X-ray Timing Explorer (RXTE) was a NASA satellite that observed the time variation of astronomical X-ray sources, named after physicist Bruno Rossi. The RXTE had three instruments — an All Sky Monitor, the High-Energy X-ray Timing ...

, 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 The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Human ...

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 The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

and asteroid studies. Small bodies, such as small

moons A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''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 Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...

. 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 The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible o ...

, observations made with Hubble, Spitzer and Chandra have been combined in the

Great Observatories Origins Deep Survey The Great Observatories Origins Deep Survey, or GOODS, is an astronomical survey combining deep observations from three of NASA's Great Observatories: the Hubble Space Telescope, the Spitzer Space Telescope, and the Chandra X-ray Observatory, al ...

to yield a multi-wavelength picture of

galaxy formation and evolution The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have gen ...

in the early

Universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. ...

. * Late 1991: Operation of both Hubble and Compton * Late 1999: Operation of Hubble, Compton, and Chandra * Mid 2000: Operation of Hubble and Chandra * Late 2003: Operation of Hubble, Chandra, and Spitzer * Early 2020: Operation of Hubble and Chandra

Synergistic discoveries

When great observatories worked together to make special discoveries or observations: Reported in March 2016, Spitzer and Hubble were used to discover the most distant-known galaxy,

GN-z11 GN-z11 is a high-redshift galaxy found in the constellation Ursa Major. It is one of the farthest known galaxies from Earth ever discovered. The 2015 discovery was published in a 2016 paper headed by Pascal Oesch and Gabriel Brammer (Cosmic Dawn ...

. This object was seen as it appeared 13.4 billion years ago. } (

List of the most distant astronomical objects This article documents the most distant astronomical objects discovered and verified so far, and the time periods in which they were so classified. For comparisons with the light travel distance of the astronomical objects listed below, the age of ...

)

Successors to GO instruments

* James Webb Space Telescope (JWST) — previously known as the NGST (Next Generation Space Telescope) launched in December 2021, and will work simultaneously with Hubble until its mission ends. 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. 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. * The

Fermi Gamma-ray Space Telescope The Fermi Gamma-ray Space Telescope (FGST, also FGRST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is ...

, formerly GLAST, the Gamma Ray Large Area Space Telescope, is a follow-on to Compton launched on 11 June 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 Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIFT, ...

, launched in 2004, will complement GLAST. The Reuven 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 The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. * Another large, high-energy observatory is

INTEGRAL In mathematics, an integral assigns numbers to functions in a way that describes displacement, area, volume, and other concepts that arise by combining infinitesimal data. The process of finding integrals is called integration. Along wit ...

, 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. SAFIR-CALISTO

Later programs

* The

Beyond Einstein program The Beyond Einstein program is a NASA project designed to explore the limits of General theory of Relativity of Albert Einstein. The project includes two space observatories, and several observational cosmology probes. The program culminates wit ...

will seek to develop new areas of science.

Constellation-X The Constellation-X Observatory (Con-X or HTXS) was a mission concept for an X-ray space observatory to be operated by NASA; in 2008 it was merged with ESA and JAXA efforts in the same direction to produce the International X-ray Observatory pr ...

and the

Laser Interferometer Space Antenna The Laser Interferometer Space Antenna (LISA) is a proposed space probe to detect and accurately measure gravitational waves—tiny ripples in the fabric of spacetime—from astronomical sources. LISA would be the first dedicated space-based gr ...

(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. * 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.

Next Great Observatory

In 2016,

began considering four different Flagship

space telescopes A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launche ...

, they are the

Habitable Exoplanet Imaging Mission The Habitable Exoplanet Observatory (HabEx) is a space telescope concept that would be optimized to search for and image Earth-size habitable exoplanets in the habitable zones of their stars, where liquid water can exist. HabEx would aim to ...

(HabEx),

Large UV Optical Infrared Surveyor The Large Ultraviolet Optical Infrared Surveyor, commonly known as LUVOIR (), is a multi-wavelength space telescope concept being developed by NASA under the leadership of a Science and Technology Definition Team. It is one of four large astro ...

(LUVOIR),

Origins Space Telescope Origins Space Telescope (Origins) is a concept study for a far-infrared survey space telescope mission.Lynx X-ray Observatory The Lynx X-ray Observatory (''Lynx'') is a NASA-funded Large Mission Concept Study commissioned as part of the National Academy of Sciences 2020 Astronomy and Astrophysics Decadal Survey. The concept study phase is complete as of August 2019, ...

. In 2019, the four teams will turn their final reports over to the National Academy of Sciences, whose independent

Decadal Survey A decadal survey is a 10-year plan outlining scientific missions and goals created by the United States National Academies. It is a summary of input from scientists in the United States and beyond. Examples include: * Astronomy and Astrophysics ...

committee advises NASA on which mission should take top priority. Selection would take place in 2021, and launch approximately in 2035.

Gallery

Image:Hubble 01.jpg, Hubble Space Telescope Image:Cartoon CGRO.jpg, Compton Gamma Ray Observatory illustration File:CGRO s37-96-010.jpg, Compton Gamma Ray Observatory, 1991 File:STS-93 Payload Bay Door Closure - GPN-2000-000854.jpg, Chandra in the Space Shuttle bay on Earth File:Faring0814 03.jpg, Spitzer on Earth being readied for launch

Notes and references

External links

*
STS-125: Final Shuttle Mission to Hubble Space Telescope

Great Observatories Interactive using WorldWide Telescope
{{Hubble Space Telescope Space telescopes NASA programs Spitzer Space Telescope Hubble Space Telescope Chandra X-ray Observatory Gamma-ray telescopes