View source for INTEGRAL

{{Short description|European space telescope for observing gamma rays}}
{{About|the satellite|integrals in calculus|Integral|other uses}}
{{Infobox spaceflight|auto=all
| name                  = International Gamma-Ray Astrophysics Laboratory (INTEGRAL)

<!--image of the spacecraft/mission-->
| image                 = INTEGRAL spacecraft model.png
| image_caption         = Artist's impression of the ''INTEGRAL'' spacecraft
| image_alt             = INTEGRAL 3D image

<!--Basic details-->
| mission_type          = [[Space observatory|Astronomy]]
| operator              = [[European Space Agency|ESA]] {{\}} [[Roscosmos|RKA]] {{\}} [[NASA]]
| COSPAR_ID             = 2002-048A
| SATCAT                = 27540
| website               = {{URL|http://sci.esa.int/integral/}}
| mission_duration      = 10 years (planned)<br>{{time interval|17 Oct 2002|28 Feb 2025|show=ymd|sep=,}} (total)

<!--Spacecraft properties-->
| manufacturer          = [[Thales Alenia Space|Alenia Spazio]]
| launch_mass           = ~ {{cvt|4000|kg|lb}}
| dry_mass              = ~ {{cvt|3450|kg|lb}}
| payload_mass          = ~ {{cvt|2000|kg|lb}}
| dimensions            = {{cvt|5.0|xx|2.8|xx|3.2|m|ft}}
| power                 = <!--end-of-life power, in watts-->

<!--Launch details-->
| launch_date           = {{start-date|17 October 2002, 01:33 UTC|timezone=yes}}<ref>{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2002-048A |title=NASA - NSSDC - Spacecraft Details |publisher=NASA |access-date=2 February 2015}}</ref>
| launch_rocket         = [[Proton-K]] [[Blok D|Blok DM2]]
| launch_site           = [[Baikonur Cosmodrome|Baikonur]] [[Baikonur Cosmodrome Site 200|Site 200/39]]
| launch_contractor     = [[Roscosmos]]

<!--end of mission-->
| disposal_type         = Decommissioned
| deactivated           = 28 February 2025
| destroyed             = <!--when craft was destroyed (if other than by re-entry)-->
| last_contact          = <!--when last signal received if not decommissioned-->
| decay_date            = 2029 (planned)

<!--orbit parameters-->
| orbit_epoch           = 17 October 2021, 05:57:43&nbsp;UTC<ref name="n2yo">{{cite web|url=http://www.n2yo.com/satellite/?s=27540|title=INTEGRAL Satellite details 2002-048A NORAD 27540|publisher=N2YO|date=17 October 2021|access-date=19 October 2021}}</ref>
| orbit_reference       = [[geocentric orbit|Geocentric]]
| orbit_regime          = [[Highly elliptical orbit|Highly elliptical]]
| orbit_semimajor       = {{convert|81116|km|mi}}<ref name="n2yo"/>
| orbit_periapsis       = {{convert|1911|km|mi}}<ref name="n2yo"/>
| orbit_apoapsis        = {{convert|147563|km|mi}}<ref name="n2yo"/>
| orbit_inclination     = 68.0&nbsp;degrees<ref name="n2yo"/>
| orbit_period          = 3,832.0&nbsp;minutes<ref name="n2yo"/>
| apsis                 = gee

<!--Telescope parameters-->
| telescope_type        = [[Coded aperture|Coded mask telescope]]
| telescope_diameter    = {{convert|3.7|m|ft}}
| telescope_focal_length= ~ {{convert|4|m|ft}}
| telescope_area        = {{convert|500|cm2|sqin|abbr=on}} (SPI, JEM-X)<br/>{{convert|3100|cm2|sqin|abbr=on}} (IBIS)
| telescope_wavelength  = 15 [[keV]] to 10 [[MeV]] (main)<br />3 to 35 keV (JEM-X)<br />500 to 580 [[Nanometre|nm]] (OMC)
| telescope_resolution  = <!--resolution of telescope-->

| instruments_list       = {{Infobox spaceflight/Instruments
 | acronym1 = ACS   | name1 = AntiCoincidence Shield
 | acronym2 = IBIS  | name2 = Imager on-Board the INTEGRAL Satellite
 | acronym3 = IREM  | name3 = INTEGRAL Radiation Environment Monitor
 | acronym4 = JEM-X | name4 = Joint European X-Ray Monitor
 | acronym5 = OMC   | name5 = Optical Monitor Camera
 | acronym6 = SPI   | name6 = SPectrometer for INTEGRAL
}}

| insignia              = File:INTEGRAL insignia.png
| insignia_caption      = ESA astrophysics insignia for ''INTEGRAL''
| insignia_alt          = INTEGRAL mission insignia

| programme             = '''[[European Space Agency Science Programme#Horizon 2000|Horizon 2000]]'''
| previous_mission      = [[Cluster II (spacecraft)|Cluster II]]
| next_mission          = ''[[Rosetta (spacecraft)|Rosetta]]''
}}
[[File:Animation of INTEGRAL trajectory.gif|thumb|right|Animation of INTEGRAL spacecraft orbit trajectory<br/>{{legend2| Lime| Earth}}{{·}}{{legend2|Magenta|INTEGRAL}}]]
The '''INTErnational Gamma-Ray Astrophysics Laboratory''' ('''INTEGRAL''') is a retired [[space telescope]] for observing [[gamma rays]] of energies up to 8 MeV. It was launched by the [[European Space Agency]] (ESA) into Earth orbit in 2002, and is designed to provide imaging and spectroscopy of cosmic sources. In the MeV energy range, it is the most sensitive [[gamma ray astronomy|gamma ray observatory]] in space.<ref>{{cite journal
| journal=American Astronomical Society, HEAD Meeting #4, #17.01; Bulletin of the American Astronomical Society
| title=INTEGRAL Observations of Gamma-Ray Bursts
| volume=31 | pages=717 |date=April 1999
| bibcode=1999HEAD....4.1701T
| last1=Teegarden|first1=B. J.|last2= Sturner|first2=S. J.}}</ref> It is sensitive to higher energy photons than X-ray instruments such as [[NuSTAR]], the [[Neil Gehrels Swift Observatory]], [[XMM-Newton]], and lower than other gamma-ray instruments such ''[[Fermi satellite|Fermi]]'' and [[High Energy Stereoscopic System|HESS]].

Photons in INTEGRAL's energy range are emitted by [[relativistic particle|relativistic]] and [[supra-thermal]]{{clarify|date=May 2020}} particles in violent sources, radioactivity from [[radioactive isotope|unstable isotopes]] produced during [[nucleosynthesis]], [[X-ray binaries]], and [[astronomical transient]]s of all types, including [[gamma-ray bursts]]. The spacecraft's instruments have very wide [[Field of view#Astronomy|fields of view]], which is particularly useful for detecting gamma-ray emission from transient sources as they can continuously monitor large parts of the sky.

INTEGRAL is an ESA mission with additional contributions from European member states including Italy, France, Germany, and Spain. Cooperation partners are the [[Russian Federal Space Agency|Russian Space Agency]] with [[Russian Space Research Institute|IKI]] (military CP Command Punkt KW) and [[NASA]].

From June 2023 until the spacecraft's retirement in 2025 INTEGRAL was able to operate despite the loss of its thrusters through the use of its [[reaction wheel]]s and [[solar radiation pressure]].<ref name="esa-20211018" /><ref name="integral-updates" />

==Mission==
Radiation more energetic than optical light, such as ultraviolet, [[X-rays]], and  [[gamma rays]], cannot penetrate Earth's atmosphere, and direct observations must be made from space. INTEGRAL is an observatory, scientists can propose for observing time of their desired target regions, data are public after a proprietary period of up to one year.

INTEGRAL was launched from the Russian [[Baikonur]] spaceport, in [[Kazakhstan]].  The 2002 launch aboard a [[Proton rocket|Proton]]-DM2 rocket achieved a 3-day elliptical orbit with an apogee of nearly 160,000&nbsp;km and a [[perigee]] of above 2,000&nbsp;km, hence mostly beyond radiation belts which would otherwise lead to high instrumental backgrounds from charged-particle activation. The spacecraft and instruments are controlled from [[ESOC]] in [[Darmstadt]], Germany, ESA's control centre, through ground stations in Belgium ([[Redu Station|Redu]]) and California ([[Goldstone Deep Space Communications Complex|Goldstone]]).

2015: Fuel usage is much lower than predictions. INTEGRAL has far exceeded its 2+3-year planned lifetime, and is set to enter Earth atmosphere in 2029 as a definite end of the mission. Its orbit was adjusted in Jan/Feb 2015 to cause such a safe (southern) reentry (due to lunar/solar perturbations, predicted for 2029), using half the remaining fuel then.<ref>{{Cite book|last=Ugo|first=Kuulkers, Erik Ferrigno, Carlo Kretschmar, Peter Alfonso-Garzon, Julia Baab, Marius Bazzano, Angela Belanger, Guillaume Benson, Ian Bird, Anthony J. Bozzo, Enrico Brandt, Soren Coe, Elliott Caballero, Isabel Cangemi, Floriane Chenevez, Jerome Cenko, Bradley Cinar, Nebil Coleiro, Alexis De Padova, Stefano Diehl, Roland Dietze, Claudia Domingo, Albert Drapes, Mark D'uva, Eleonora Ehle, Matthias Ebrero, Jacobo Edirimanne, Mithrajith Eismont, Natan A. Finn, Timothy Fiocchi, Mariateresa Tomas, Elena Garcia Gaudenzi, Gianluca Godard, Thomas Goldwurm, Andrea Gotz, Diego Gouiffes, Christian Grebenev, Sergei A. Greiner, Jochen Gros, Aleksandra Hanlon, Lorraine Hermsen, Wim Hernandez, Cristina Hernanz, Margarita Huebner, Jutta Jourdain, Elisabeth La Rosa, Giovanni Labanti, Claudio Laurent, Philippe Lehanka, Alexander Lund, Niels Madison, James Malzac, Julien Martin, Jim Mas-Hesse, J. Miguel McBreen, Brian McDonald, Alastair McEnery, Julie Mereghetti, Sandro Natalucci, Lorenzo Ness, Jan-Uwe Oxborrow, Carol Anne Palmer, John Peschke, Sibylle Petrucciani, Francesco Pfeil, Norbert Reichenbaecher, Michael Rodi, James Rodriguez, Jerome Roques, Jean-Pierre Donate, Emilio Salazar Salt, Dave Sanchez-Fernandez, Celia Sauvageon, Aymeric Savchenko, Volodymyr Sazonov, Sergey Yu. Scaglioni, Stefano Schartel, Norbert Siegert, Thomas Southworth, Richard Sunyaev, Rashid A. Toma, Liviu Ubertini, Pietro Heuvel, Ed P. J. van den von Kienlin, Andreas von Krusenstiern, Nikolai Winkler, Christoph Wojciech, Hajdas Zannoni|url=http://worldcat.org/oclc/1262720738|title=INTEGRAL reloaded: spacecraft, instruments and ground system|date=2021-06-23|oclc=1262720738}}</ref><ref>{{Cite book|last1=Huebner|first1=Jutta M.|last2=Southworth|first2=Richard T.|last3=Salt|first3=David J.|last4=Dietze|first4=Claudia|last5=McDonald|first5=Alastair|last6=Merz|first6=Klaus|last7=Ziegler|first7=Gerald|title=SpaceOps 2016 Conference |chapter=Clean-up your space: INTEGRAL low cost end-of-life disposal |date=2016-05-13|url=http://dx.doi.org/10.2514/6.2016-2359 |location=Reston, Virginia|publisher=American Institute of Aeronautics and Astronautics|doi=10.2514/6.2016-2359|isbn=978-1-62410-426-8}}</ref>

In July 2020 INTEGRAL put itself in safe-mode, and it seemed the thrusters had failed. Since then alternative algorithms to slew and unload the [[reaction wheel]]s have been developed and tested.<ref name=SD_2021>[https://www.spacedaily.com/reports/Rescuing_Integral_No_thrust_No_problem_999.html "Rescuing Integral: No thrust? No problem" July 2021]</ref>

In September 2021 a [[single event upset]] triggered a sequence of events that put INTEGRAL into an uncontrolled tumbling state, considered to be a 'mission critical anomaly'. The operations team used the reaction wheels to recover attitude control.<ref name="esa-20211018">{{cite web |url=https://www.esa.int/Enabling_Support/Operations/Three_hours_to_save_Integral |title=Three hours to save Integral |work=ESA |date=18 October 2021 |access-date=19 October 2021}}</ref><ref name="integral-updates">{{cite web |url=https://www.cosmos.esa.int/web/integral |title=Integral Latest News |work=ESA |date=1 October 2021 |access-date=19 October 2021}}</ref>

In March 2023, INTEGRAL science operations were extended to the end of 2024, which will be followed by a two-year post-operations phase and further monitoring of the spacecraft until its estimated reentry in February 2029.<ref name="esa-20230307">{{cite web |url=https://sci.esa.int/web/director-desk/-/extended-life-for-esa-s-science-missions |title=Extended life for ESA's science missions |work=[[ESA]] |date=7 March 2023 |access-date=20 March 2023}}</ref>

Also in March 2023, a new software based safe mode was tested that would use reaction wheels (rather than the failed thrusters).<ref>[https://www.spacedaily.com/reports/Integral_safe_at_last_999.html ''Integral safe at last'']</ref>

On 28 February 2025, science observations with the INTEGRAL spacecraft were officially ended.<ref>[https://www.spacedaily.com/reports/Mission_accomplished_for_Integral_ESAs_gamma_ray_telescope_999.html Mission accomplished for Integral, ESA's gamma-ray telescope]</ref>

==Spacecraft==
[[File:Integral instruments.jpg|thumb|Integral instruments]]
The spacecraft body ("service module") is a copy of the [[XMM-Newton]] body. This saved development costs and simplified integration with infrastructure and ground facilities. An adapter was necessary to mate with the different launch vehicle, though. However, the denser instruments used for gamma rays and hard X-rays make INTEGRAL the heaviest scientific payload ever flown by ESA.

The body is constructed largely of composites.  Propulsion is by a [[hydrazine]] [[monopropellant]] system, containing 544&nbsp;kg of fuel in four exposed tanks.  The titanium tanks were charged with gas to 24 [[Bar (unit)|bar]] (2.4&nbsp;[[megapascal|MPa]]) at 30&nbsp;°C, and have tank diaphragms. Attitude control is via a [[star tracker]], multiple [[Sun sensor]]s (ESM), and multiple [[momentum wheel]]s. The dual solar arrays, spanning 16 meters when deployed and producing 2.4&nbsp;kW at beginning of life (BoL), are backed up by dual [[nickel-cadmium battery]] sets.

The instrument structure ("payload module") is also composite. A rigid base supports the detector assemblies, and an H-shaped structure holds the coded masks approximately 4 meters above their detectors. The payload module can be built and tested independently from the service module, reducing cost.

[[Alenia Spazio]] (now Thales Alenia Space Italia) was the spacecraft prime contractor.

==Instruments==
Four instruments with large fields-of-view are co-aligned on this platform, to study targets across such a wide energy range of almost two orders of magnitude in energy (other astronomy instruments in X-rays or optical cover much smaller ranges of factors of a few at most).  Imaging is achieved by [[coded aperture|coded masks]] casting a shadowgram onto pixelised cameras; the tungsten masks were provided by the University of Valencia, Spain.

The INTEGRAL imager, '''IBIS''' (Imager on-Board the INTEGRAL Satellite) observes from 15 [[keV]] (hard X-rays) to 10 [[MeV]] (gamma rays).  Angular resolution is 12 arcmin, enabling a bright source to be located to better than 1 arcmin.  A 95 x 95 mask of rectangular [[tungsten]] tiles sits 3.2 meters above the detectors.  The detector system contains a forward plane of 128 x 128 Cadmium-Telluride tiles (ISGRI- Integral Soft Gamma-Ray Imager), backed by a 64 x 64 plane of Caesium-Iodide tiles (PICsIT- Pixellated Caesium-Iodide Telescope).  ISGRI is sensitive up to 1 MeV, while PICsIT extends to 10 MeV.  Both are surrounded by passive shields of tungsten and lead. IBIS was provided by PI institutes in Rome/Italy and Paris/France.

[[File:HURA_hexagonal_coded_aperture_mask_principle.svg|thumb|Simplified principle of operation of a HURA hexagonal coded aperture mask used in SPI]]
The spectrometer aboard INTEGRAL is '''SPI''', the SPectrometer of INTEGRAL. It was conceived and assembled by the French Space Agency [[CNES]], with PI institutes in Toulouse/France and Garching/Germany. It observes radiation between 20 [[keV]] and 8 [[MeV]].  SPI has a [[coded mask]] of hexagonal [[tungsten]] tiles, above a detector plane of 19 [[germanium]] crystals (also packed hexagonally).  The high energy resolution of 2 keV at 1 MeV is capable to resolve all candidate gamma-ray lines. The Ge crystals are actively cooled with a mechanical system of Stirling coolers to about 80K.

IBIS and SPI use active detectors to detect and veto charged particles that lead to background radiation.  The SPI '''ACS''' (AntiCoincidence Shield) consists of a BGO scintillator blocks surrounding the camera and aperture, detecting all charged particles, and photons exceeding an energy of about 75 keV, that would hit the instrument from directions different from the aperture.  A thin layer of plastic [[scintillator]] behind the tungsten tiles serves as additional charged-particle detector within the aperture.

The large effective area of the ACS turned out to be useful as an instrument in its own right.  Its all-sky coverage and sensitivity make it a natural [[gamma-ray burst]] detector, and a valued component of the [[InterPlanetary Network|IPN]] (InterPlanetary Network).

Dual '''JEM-X''' units provide additional information on sources at soft and hard X-rays, from 3 to 35 keV.  Aside from broadening the spectral coverage, imaging is more precise due to the shorter wavelength.  Detectors are gas scintillators ([[xenon]] plus [[methane]]) in a microstrip layout, below a mask of hexagonal tiles.

INTEGRAL includes an Optical Monitor ('''OMC''') instrument, sensitive from 500 to 580 [[nanometer|nm]]. It acts as both a framing aid, and can note the activity and state of some brighter targets, e.g. it had been useful to monitor supernova light over months from SN2014J.

The spacecraft also includes a radiation monitor, INTEGRAL Radiation Environment Monitor ('''IREM'''), to note the orbital background for calibration purposes.  IREM has an electron and a proton channel, though radiation up to [[cosmic rays]] can be sensed.  Should the background exceed a preset threshold, IREM can shut down the instruments.

==Scientific results==
INTEGRAL contributes to multi-messenger astronomy, detecting gamma rays from the first merger of two neutron stars observed in gravitational waves, and from a [[fast radio burst]].<ref>{{Cite book|last=Savchenko|first=Volodymyr|title=Proceedings of the New Era of Multi-Messenger Astrophysics — PoS(Asterics2019) |chapter=Hunting for elusive multi-messenger transients with INTEGRAL |date=2019-10-29 |volume=90 |page=071 |doi=10.22323/1.357.0071|s2cid=213420364|doi-access=free}}</ref><ref>{{cite journal |bibcode=2019MmSAI..90...19S |title=Hunting for elusive multi-messenger transients with INTEGRAL |last1=Savchenko |first1=Volodymyr |journal=Memorie della Societa Astronomica Italiana |date=2019 |volume=90 |page=19 |display-authors=etal }}</ref> By 2025, 2258 refereed papers were published that benefit from INTEGRAL data which corresponds on average to one paper every 3.5 days.<ref>https://ui.adsabs.harvard.edu/public-libraries/5oYLIENpRxC8S38Btgo-fw</ref>

== See also ==
* [[BOOTES]]
* [[List of X-ray space telescopes]]

==References==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20130327210832/http://sci.esa.int/science-e/www/area/index.cfm?fareaid=21 INTEGRAL] at ESA (archived in 2013)
* [https://integral.cnes.fr/fr/home-45 INTEGRAL overview] at CNES (French Space Agency)
* [http://www.esa.int/SPECIALS/Operations/SEM33HZTIVE_0.html Integral operations page] at ESA. Says "the currently planned end of mission is December 2014" !
* [http://www.isdc.unige.ch/integral/ INTEGRAL] at the ISDC (INTEGRAL Science Data Centre)
* [https://web.archive.org/web/20080925020452/http://solarsystem.nasa.gov/missions/profile.cfm?MCode=INTEGRAL INTEGRAL Mission Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2002-048A NSSDC overview page]
* [https://web.archive.org/web/20120206104653/http://smsc.cnes.fr/SPI/ SPI/INTEGRAL] more information on SPI the spectrometer for INTEGRAL
* [http://www.iasfbo.inaf.it/extras/IGR/main.html A Catalogue of INTEGRAL Sources] INTEGRAL Sources identified through optical and near-infrared spectroscopy
* [https://www.eoportal.org/satellite-missions/integral INTEGRAL article on eoPortal by ESA]

{{Space observatories}}
{{ESA projects}}
{{Explorers program}}
{{Orbital launches in 2002}}
{{Authority control}}

{{DEFAULTSORT:Integral}}
[[Category:European Space Agency satellites]]
[[Category:Space telescopes]]
[[Category:X-ray telescopes]]
[[Category:Gamma-ray telescopes]]
[[Category:Spacecraft launched in 2002]]
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