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32-561: 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-rays and gamma rays , including various specialized sub-instruments and detectors. Following 14 years of effort, the observatory was launched from Space Shuttle Atlantis during STS-37 on April 5, 1991, and operated until its deorbit on June 4, 2000. It

64-458: A phoswich : i.e., particle and gamma-ray events from the rear produced slow-rise time (~1 μs) pulses, which could be electronically distinguished from pure NaI events from the front, which produced faster (~0.25 μs) pulses. Thus the CsI backing crystal acted as an active anticoincidence shield, vetoing events from the rear. A further barrel-shaped CsI shield, also in electronic anticoincidence, surrounded

96-514: A complement of four instruments that covered an unprecedented six orders of the electromagnetic spectrum , from 20 keV to 30 GeV (from 0.02 MeV to 30000 MeV). Those are presented below in order of increasing spectral energy coverage: The Burst and Transient Source Experiment ( BATSE ) by NASA's Marshall Space Flight Center searched the sky for gamma-ray bursts (20 to >600 keV) and conducted full-sky surveys for long-lived sources. It consisted of eight identical detector modules, one at each of

128-426: A direction to the sky, and the angle θ about this direction, defined a cone about V on which the source of the photon must lie, and a corresponding "event circle" on the sky. Because of the requirement for a near coincidence between the two interactions, with the correct delay of a few nanoseconds, most modes of background production were strongly suppressed. From the collection of many event energies and event circles,

160-469: A field of view of one steradian . For cosmic gamma-ray events, the experiment required two nearly simultaneous interactions, in a set of front and rear scintillators. Gamma rays would Compton scatter in a forward detector module, where the interaction energy E 1 , given to the recoil electron was measured, while the Compton scattered photon would then be caught in one of the second layers of scintillators to

192-521: A map of the positions of sources, along with their photon fluxes and spectra, could be determined. The Energetic Gamma Ray Experiment Telescope ( EGRET ) measured high energy (20 MeV to 30 GeV) gamma-ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA Goddard Space Flight Center , the Max Planck Institute for Extraterrestrial Physics , and Stanford University . Its detector operated on

224-455: A result, the angular resolution of space telescopes is often much higher than a ground-based telescope with a similar aperture . Many larger terrestrial telescopes, however, reduce atmospheric effects with adaptive optics . Space-based astronomy is more important for frequency ranges that are outside the optical window and the radio window , the only two wavelength ranges of the electromagnetic spectrum that are not severely attenuated by

256-474: A satellite. Space observatory In 1946, American theoretical astrophysicist Lyman Spitzer , "father of Hubble" proposed to put a telescope in space. Spitzer's proposal called for a large telescope that would not be hindered by Earth's atmosphere. After lobbying in the 1960s and 70s for such a system to be built, Spitzer's vision ultimately materialized into the Hubble Space Telescope , which

288-500: A speed of approximately 2 degrees per second. The Imaging Compton Telescope ( COMPTEL ) by the Max Planck Institute for Extraterrestrial Physics , the University of New Hampshire , Netherlands Institute for Space Research , and ESA's Astrophysics Division was tuned to the 0.75-30 MeV energy range and determined the angle of arrival of photons to within a degree and the energy to within five percent at higher energies. The instrument had

320-486: Is 3.5 cm. It exhibits two main emission components: one in the near ultraviolet region at the wavelength of 310 nm and one at 460 nm. The drawbacks of CsI are a high temperature gradient and a slight hygroscopicity . Caesium iodide is used as a beamsplitter in Fourier transform infrared (FTIR) spectrometers. It has a wider transmission range than the more common potassium bromide beamsplitters, working range into

352-433: Is CsCl for mica and NaCl for LiF, NaBr and NaCl substrates. Caesium iodide atomic chains can be grown inside double-wall carbon nanotubes . In such chains I atoms appear brighter than Cs atoms in electron micrographs despite having a smaller mass. This difference was explained by the charge difference between Cs atoms (positive), inner nanotube walls (negative) and I atoms (negative). As a result, Cs atoms are attracted to

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384-410: Is the ionic compound of caesium and iodine . It is often used as the input phosphor of an X-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths. Bulk caesium iodide crystals have the cubic CsCl crystal structure, but the structure type of nanometer-thin CsI films depends on the substrate material – it

416-636: The CNSA , scientists fear that there would be gaps in coverage that would not be covered immediately by future projects and this would affect research in fundamental science. On 16 January 2023, NASA announced preliminary considerations of several future space telescope programs, including the Great Observatory Technology Maturation Program, Habitable Worlds Observatory , and New Great Observatories. Caesium iodide Caesium iodide or cesium iodide ( chemical formula CsI )

448-554: The Naval Research Laboratory detected gamma rays entering the field of view of any of four detector modules, which could be pointed individually, and were effective in the 0.05 to 10 MeV range. Each detector had a central scintillation spectrometer crystal of NaI(Tl) 12 in (303 mm) in diameter, by 4 in (102 mm) thick, optically coupled at the rear to a 3 in (76.2 mm) thick CsI (Na) crystal of similar diameter, viewed by seven photomultiplier tubes , operated as

480-464: The LAD rates triggered a high-speed data storage mode, the details of the burst being read out to telemetry later. Bursts were typically detected at rates of roughly one per day over the 9-year CGRO mission. A strong burst could result in the observation of many thousands of gamma-rays within a time interval ranging from ~0.1 s up to about 100 s. The Oriented Scintillation Spectrometer Experiment ( OSSE ) by

512-486: The Soviet Orion 1 ultraviolet telescope aboard space station Salyut 1 in 1971. Performing astronomy from ground-based observatories on Earth is limited by the filtering and distortion of electromagnetic radiation ( scintillation or twinkling) due to the atmosphere . A telescope orbiting Earth outside the atmosphere is subject neither to twinkling nor to light pollution from artificial light sources on Earth. As

544-621: The atmosphere. For example, X-ray astronomy is nearly impossible when done from Earth, and has reached its current importance in astronomy only due to orbiting X-ray telescopes such as the Chandra X-ray Observatory and the XMM-Newton observatory . Infrared and ultraviolet are also largely blocked. Space telescopes are much more expensive to build than ground-based telescopes. Due to their location, space telescopes are also extremely difficult to maintain. The Hubble Space Telescope

576-446: The central detector on the sides and provided coarse collimation, rejecting gamma rays and charged particles from the sides or most of the forward field-of-view (FOV). A finer level of angular collimation was provided by a tungsten slat collimator grid within the outer CsI barrel, which collimated the response to a 3.8° x 11.4° FWHM rectangular FOV. A plastic scintillator across the front of each module vetoed charged particles entering from

608-416: The direct conversion of approximately two solar masses into energy. This finally convinced the community that GRB afterglows resulted from highly collimated explosions, which strongly reduced the needed energy budget. It was deployed to an altitude of 450 km on April 7, 1991, when it was first launched. Over time the orbit decayed and needed re-boosting to prevent atmospheric entry sooner than desired. It

640-399: The front. The four detectors were typically operated in pairs of two. During a gamma-ray source observation, one detector would take observations of the source, while the other would slew slightly off source to measure the background levels. The two detectors would routinely switch roles, allowing for more accurate measurements of both the source and background. The instruments could slew with

672-475: The interest of public safety that a controlled crash into an ocean was preferable to letting the craft come down on its own at random. It entered the Earth's atmosphere on 4 June 2000, with the debris that did not burn up ("six 1,800-pound aluminum I-beams and parts made of titanium, including more than 5,000 bolts") falling into the Pacific Ocean. This de-orbit was NASA's first intentional controlled de-orbit of

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704-453: The principle of electron- positron pair production from high energy photons interacting in the detector. The tracks of the high-energy electron and positron created were measured within the detector volume, and the axis of the V of the two emerging particles projected to the sky. Finally, their total energy was measured in a large calorimeter scintillation detector at the rear of the instrument. Gamma ray burst 990123 (23 January 1999)

736-404: The rear, where its total energy, E 2 , would be measured. From these two energies, E 1 and E 2 , the Compton scattering angle, angle θ, can be determined, along with the total energy, E 1 + E 2 , of the incident photon. The positions of the interactions, in both the front and rear scintillators, was also measured. The vector , V , connecting the two interaction points determined

768-458: The satellite's corners. Each module consisted of both a NaI(Tl) Large Area Detector (LAD) covering the 20 keV to ~2 MeV range, 50.48 cm in dia by 1.27 cm thick, and a 12.7 cm dia by 7.62 cm thick NaI Spectroscopy Detector, which extended the upper energy range to 8 MeV, all surrounded by a plastic scintillator in active anti-coincidence to veto the large background rates due to cosmic rays and trapped radiation. Sudden increases in

800-409: The walls and vibrate more strongly than I atoms, which are pushed toward the nanotube axis. An important application of caesium iodide crystals , which are scintillators , is electromagnetic calorimetry in experimental particle physics . Pure CsI is a fast and dense scintillating material with relatively low light yield that increases significantly with cooling, and a fairly small Molière radius

832-583: Was an international collaboration and additional contributions came from the European Space Agency and various universities, as well as the U.S. Naval Research Laboratory . Successors to CGRO include the ESA INTEGRAL spacecraft (launched 2002), NASA's Swift Gamma-Ray Burst Mission (launched 2004), ASI AGILE (satellite) (launched 2007) and NASA's Fermi Gamma-ray Space Telescope (launched 2008); all remain operational as of May 2023. CGRO carried

864-571: Was deployed in low Earth orbit at 450 km (280 mi) to avoid the Van Allen radiation belt . It was the heaviest astrophysical payload ever flown at that time at 16,300 kilograms (35,900 lb). Costing $ 617 million, the CGRO was part of NASA 's Great Observatories series, along with the Hubble Space Telescope , the Chandra X-ray Observatory , and the Spitzer Space Telescope . It

896-628: Was launched on April 24, 1990, by the Space Shuttle Discovery (STS-31). This was launched due to many efforts by Nancy Grace Roman, "mother of Hubble", who was the first Chief of Astronomy and first female executive at NASA. She was a program scientist that worked to convince NASA, Congress, and others that Hubble was "very well worth doing". The first operational space telescopes were the American Orbiting Astronomical Observatory , OAO-2 launched in 1968, and

928-420: Was one of the brightest bursts recorded at the time, and was the first GRB with an optical afterglow observed during the prompt gamma ray emission (a reverse shock flash). This allowed astronomers to measure a redshift of 1.6 and a distance of 3.2 Gpc. Combining the measured energy of the burst in gamma-rays and the distance, the total emitted energy assuming an isotropic explosion could be deduced and resulted in

960-654: Was reboosted twice using onboard propellant: in October 1993 from 340 km to 450 km altitude, and in June 1997 from 440 km to 515 km altitude, to potentially extend operation to 2007. After one of its three gyroscopes failed in December 1999, the observatory was deliberately de-orbited. At the time, the observatory was still operational; however the failure of another gyroscope would have made de-orbiting much more difficult and dangerous. With some controversy, NASA decided in

992-658: Was serviced by the Space Shuttle , but most space telescopes cannot be serviced at all. Satellites have been launched and operated by NASA , ISRO , ESA , CNSA , JAXA and the Soviet space program (later succeeded by Roscosmos of Russia). As of 2022, many space observatories have already completed their missions, while others continue operating on extended time. However, the future availability of space telescopes and observatories depends on timely and sufficient funding. While future space observatories are planned by NASA, JAXA and

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1024-612: Was the second of the series to be launched into space, following the Hubble Space Telescope. The CGRO was named after Arthur Compton , an American physicist and former chancellor of Washington University in St. Louis who received the Nobel prize for work involved with gamma-ray physics. CGRO was built by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach , California . CGRO

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