International Gamma-Ray Astrophysics Laboratory (INTEGRAL)

Artist's impression of theINTEGRAL spacecraft
Mission type	Astronomy
Operator	ESA  / RKA  / NASA
COSPAR ID	2002-048A
SATCATno.	27540
Website	sci.esa.int/integral/
Mission duration	10 years (planned) 22 years, 4 months, 11 days (total)
Spacecraft properties
Manufacturer	Alenia Spazio
Launch mass	~ 4,000 kg (8,800 lb)
Dry mass	~ 3,450 kg (7,610 lb)
Payload mass	~ 2,000 kg (4,400 lb)
Dimensions	5.0 × 2.8 × 3.2 m (16.4 × 9.2 × 10.5 ft)
Start of mission
Launch date	17 October 2002, 01:33 UTC (2002-10-17UTC01:33Z)[1]
Rocket	Proton-KBlok DM2
Launch site	BaikonurSite 200/39
Contractor	Roscosmos
End of mission
Disposal	Decommissioned
Deactivated	28 February 2025
Decay date	2029 (planned)
Orbital parameters
Reference system	Geocentric
Regime	Highly elliptical
Semi-major axis	81,116 kilometres (50,403 mi)[2]
Perigee altitude	1,911 kilometres (1,187 mi)[2]
Apogee altitude	147,563 kilometres (91,691 mi)[2]
Inclination	68.0 degrees[2]
Period	3,832.0 minutes[2]
Epoch	17 October 2021, 05:57:43 UTC[2]
Main telescope
Type	Coded mask telescope
Diameter	3.7 metres (12 ft)
Focal length	~ 4 metres (13 ft)
Collecting area	500 cm2 (78 sq in) (SPI, JEM-X) 3,100 cm2 (480 sq in) (IBIS)
Wavelengths	15keV to 10MeV (main) 3 to 35 keV (JEM-X) 500 to 580nm (OMC)
Instruments ACS AntiCoincidence Shield IBIS Imager on-Board the INTEGRAL Satellite IREM INTEGRAL Radiation Environment Monitor JEM-X Joint European X-Ray Monitor OMC Optical Monitor Camera SPI SPectrometer for INTEGRAL
ESA astrophysics insignia forINTEGRAL Horizon 2000 ← Cluster II Rosetta →

TheINTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a retiredspace telescope for observinggamma rays of energies up to 8 MeV. It was launched by theEuropean 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 sensitivegamma ray observatory in space.^[3] It is sensitive to higher energy photons than X-ray instruments such asNuSTAR, theNeil Gehrels Swift Observatory,XMM-Newton, and lower than other gamma-ray instruments suchFermi andHESS.

Photons in INTEGRAL's energy range are emitted byrelativistic andsupra-thermal^{[clarification needed]} particles in violent sources, radioactivity fromunstable isotopes produced duringnucleosynthesis,X-ray binaries, andastronomical transients of all types, includinggamma-ray bursts. The spacecraft's instruments have very widefields 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 theRussian Space Agency withIKI (military CP Command Punkt KW) andNASA.

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 itsreaction wheels andsolar radiation pressure.^[4][5]

Radiation more energetic than optical light, such as ultraviolet,X-rays, andgamma 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 RussianBaikonur spaceport, inKazakhstan. The 2002 launch aboard aProton-DM2 rocket achieved a 3-day elliptical orbit with an apogee of nearly 160,000 km and aperigee of above 2,000 km, hence mostly beyond radiation belts which would otherwise lead to high instrumental backgrounds from charged-particle activation. The spacecraft and instruments are controlled fromESOC inDarmstadt, Germany, ESA's control centre, through ground stations in Belgium (Redu) and California (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.^[6][7]

In July 2020 INTEGRAL put itself in safe-mode, and it seemed the thrusters had failed. Since then alternative algorithms to slew and unload thereaction wheels have been developed and tested.^[8]

In September 2021 asingle 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.^[4][5]

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.^[9]

Also in March 2023, a new software based safe mode was tested that would use reaction wheels (rather than the failed thrusters).^[10]

On 28 February 2025, science observations with the INTEGRAL spacecraft were officially ended.^[11]

The spacecraft body ("service module") is a copy of theXMM-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 ahydrazinemonopropellant system, containing 544 kg of fuel in four exposed tanks. The titanium tanks were charged with gas to 24bar (2.4 MPa) at 30 °C, and have tank diaphragms. Attitude control is via astar tracker, multipleSun sensors (ESM), and multiplemomentum wheels. The dual solar arrays, spanning 16 meters when deployed and producing 2.4 kW at beginning of life (BoL), are backed up by dualnickel-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.

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 bycoded 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 15keV (hard X-rays) to 10MeV (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 rectangulartungsten 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.

The spectrometer aboard INTEGRAL isSPI, the SPectrometer of INTEGRAL. It was conceived and assembled by the French Space AgencyCNES, with PI institutes in Toulouse/France and Garching/Germany. It observes radiation between 20keV and 8MeV. SPI has acoded mask of hexagonaltungsten tiles, above a detector plane of 19germanium 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 SPIACS (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 plasticscintillator 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 naturalgamma-ray burst detector, and a valued component of theIPN (InterPlanetary Network).

DualJEM-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 plusmethane) in a microstrip layout, below a mask of hexagonal tiles.

INTEGRAL includes an Optical Monitor (OMC) instrument, sensitive from 500 to 580nm. 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 tocosmic rays can be sensed. Should the background exceed a preset threshold, IREM can shut down the instruments.

INTEGRAL contributes to multi-messenger astronomy, detecting gamma rays from the first merger of two neutron stars observed in gravitational waves, and from afast radio burst.^[12][13] By 2025, 2258 refereed papers were published that benefit from INTEGRAL data which corresponds on average to one paper every 3.5 days.^[14]

• BOOTES
• List of X-ray space telescopes

• INTEGRAL at ESA (archived in 2013)
• INTEGRAL overview at CNES (French Space Agency)
• Integral operations page at ESA. Says "the currently planned end of mission is December 2014" !
• INTEGRAL at the ISDC (INTEGRAL Science Data Centre)
• INTEGRAL Mission Profile byNASA's Solar System Exploration
• NSSDC overview page
• SPI/INTEGRAL more information on SPI the spectrometer for INTEGRAL
• A Catalogue of INTEGRAL Sources INTEGRAL Sources identified through optical and near-infrared spectroscopy
• INTEGRAL article on eoPortal by ESA

• European Space Agency satellites
• Space telescopes
• X-ray telescopes
• Gamma-ray telescopes
• Spacecraft launched in 2002
• Explorers Program

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• Wikipedia articles needing clarification from May 2020