Compton Gamma Ray Observatory

Last updated

Compton Gamma Ray Observatory
CGRO s37-96-010.jpg
CGRO deployed in 1991
Mission typeAstronomy
Operator NASA
COSPAR ID 1991-027B OOjs UI icon edit-ltr-progressive.svg
SATCAT no. 21225
Website cossc.gsfc.nasa.gov
Mission duration9 years, 2 months
Spacecraft properties
Manufacturer TRW Inc.
Launch mass17,000 kilograms (37,000 lb)
Power2000.0 Watts [1]
Start of mission
Launch date5 April 1991, 14:22:45 (1991-04-05UTC14:22:45Z) UTC
Rocket Space Shuttle Atlantis
STS-37
Launch site Kennedy LC-39B
End of mission
Decay date4 June 2000, 23:29:55 (2000-06-04UTC23:29:56) UTC
Orbital parameters
Reference system Geocentric
Regime Low Earth
Eccentricity 0.006998
Perigee altitude 362 kilometres (225 mi)
Apogee altitude 457 kilometres (284 mi)
Inclination 28.4610 degrees
Period 91.59 minutes
RAAN 68.6827 degrees
Epoch 7 April 1991, 18:37:00 UTC [2]
Main Telescopes (Four)
TypeScintillation detectors
Focal lengthVaried by instrument
Collecting areaVaried by instrument
Wavelengths X-ray to γ-ray, 20  keV – 30 GeV (40  pm – 60  am)
Instruments
BATSE, OSSE, COMPTEL, EGRET
 
Launch of Atlantis carrying the observatory to Earth orbit (STS-37) STS-37 Launch.jpg
Launch of Atlantis carrying the observatory to Earth orbit (STS-37)
Astronaut Jay Apt in the Space Shuttle bay with the observatory partially deployed but still attached to the Shuttle's robotic arm NASA image STS37-051-021 Jay Apt on the first EVA of STS-37 with CGRO.jpg
Astronaut Jay Apt in the Space Shuttle bay with the observatory partially deployed but still attached to the Shuttle's robotic arm

The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting photons with energies from 20 keV 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. [3] It 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 17,000 kilograms (37,000 lb).

Contents

Costing $617 million, [4] 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. [5] It 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 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 2019.

Instruments

CGRO carried 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:

BATSE

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 the satellite's corners. [6] 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 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.

OSSE

The Oriented Scintillation Spectrometer Experiment (OSSE) by 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 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 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 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 a speed of approximately 2 degrees per second.

COMPTEL

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 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 E1, 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 the rear, where its total energy, E2, would be measured. From these two energies, E1 and E2, the Compton scattering angle, angle θ, can be determined, along with the total energy, E1 + E2, 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 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, a map of the positions of sources, along with their photon fluxes and spectra, could be determined.

EGRET

Instruments
InstrumentObserving
BATSE0.02 – 8 MeV
OSSE0.05 – 10 MeV
COMPTEL0.75 – 30 MeV
EGRET20 – 30 000 MeV

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 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.

Results

The Moon as seen by the Compton Gamma Ray Observatory, in gamma rays of greater than 20 MeV. These are produced by cosmic ray bombardment of its surface. The Sun, which has no similar surface of high atomic number to act as target for cosmic rays, cannot be seen at all at these energies, which are too high to emerge from primary nuclear reactions, such as solar nuclear fusion. Moon egret.jpg
The Moon as seen by the Compton Gamma Ray Observatory, in gamma rays of greater than 20 MeV. These are produced by cosmic ray bombardment of its surface. The Sun, which has no similar surface of high atomic number to act as target for cosmic rays, cannot be seen at all at these energies, which are too high to emerge from primary nuclear reactions, such as solar nuclear fusion.

Basic results

GRB 990123

Gamma ray burst 990123 (23 January 1999) 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 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.

Miscellaneous results

History

Proposal
Work started in 1977.
Funding and Development
CGRO was designed for in-orbit refuelling/servicing. [8]
Construction and test
Launch and Commissioning
Launched 7 April 1991. Fuel line problems were found soon after launch which discouraged frequent orbital reboosts.
Communications
Loss of data tape recorder, and mitigation
Onboard data recorders failed in 1992 which reduced the amount of data that could be downlinked. Another TDRS ground station was built to reduce the gaps in data collection. [9]

Orbital re-boost

Compton Gamma Ray Observatory being deployed from Space Shuttle Atlantis in 1991 in Earth orbit 1991 s37 GRO copy.jpg
Compton Gamma Ray Observatory being deployed from Space Shuttle Atlantis in 1991 in Earth orbit

It was deployed to an altitude of 450 km on April 7, 1991 when it was first launched. [10] Over time the orbit decayed and needed re-boosting to prevent atmospheric entry sooner than desired. [10] It 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. [10]

De-orbit

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 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. [4] 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. [11]

This de-orbit was NASA's first intentional controlled de-orbit of a satellite. [12]

See also

Related Research Articles

<span class="mw-page-title-main">BeppoSAX</span> Italian-Dutch satellite used for X-ray astronomy

BeppoSAX was an Italian–Dutch satellite for X-ray astronomy which played a crucial role in resolving the origin of gamma-ray bursts (GRBs), the most energetic events known in the universe. It was the first X-ray mission capable of simultaneously observing targets over more than 3 decades of energy, from 0.1 to 300 kiloelectronvolts (keV) with relatively large area, good energy resolution and imaging capabilities. BeppoSAX was a major programme of the Italian Space Agency (ASI) with the participation of the Netherlands Agency for Aerospace Programmes (NIVR). The prime contractor for the space segment was Alenia while Nuova Telespazio led the development of the ground segment. Most of the scientific instruments were developed by the Italian National Research Council (CNR) while the Wide Field Cameras were developed by the Netherlands Institute for Space Research (SRON) and the LECS was developed by the astrophysics division of the European Space Agency's ESTEC facility.

<span class="mw-page-title-main">Fermi Gamma-ray Space Telescope</span> Space telescope for gamma-ray astronomy launched in 2008

The Fermi Gamma-ray Space Telescope, 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 the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor, is being used to study gamma-ray bursts and solar flares.

<span class="mw-page-title-main">STS-37</span> 1991 American crewed spaceflight to deploy the Compton Gamma Ray Observatory

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 Observatories program which included the visible-spectrum Hubble Space Telescope (HST), the Chandra X-ray Observatory (CXO) and the infrared Spitzer Space Telescope. The mission also featured two spacewalks, the first since 1985.

<span class="mw-page-title-main">Great Observatories program</span> Series of NASA satellites

NASA's series of Great Observatories satellites are four large, powerful 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 rays, X-rays, visible and ultraviolet light, and infrared light.

<span class="mw-page-title-main">Gamma-ray spectrometer</span>

A gamma-ray spectrometer (GRS) is an instrument for measuring the distribution of the intensity of gamma radiation versus the energy of each photon. The study and analysis of gamma-ray spectra for scientific and technical use is called gamma spectroscopy, and gamma-ray spectrometers are the instruments which observe and collect such data. Because the energy of each photon of EM radiation is proportional to its frequency, gamma rays have sufficient energy that they are typically observed by counting individual photons.

<span class="mw-page-title-main">Ramaty High Energy Solar Spectroscopic Imager</span> NASA satellite of the Explorer program

Ramaty High Energy Solar Spectroscopic Imager was a NASA solar flare observatory. It was the sixth mission in the Small Explorer program (SMEX), selected in October 1997 and launched on 5 February 2002, at 20:58:12 UTC. Its primary mission was to explore the physics of particle acceleration and energy release in solar flares.

<span class="mw-page-title-main">Neil Gehrels Swift Observatory</span> NASA satellite of the Explorer program

Neil Gehrels Swift Observatory, previously called the Swift Gamma-Ray Burst Explorer, is a NASA three-telescope space observatory for studying gamma-ray bursts (GRBs) and monitoring the afterglow in X-ray, and UV/Visible light at the location of a burst. It was launched on 20 November 2004, aboard a Delta II launch vehicle. Headed by principal investigator Neil Gehrels until his death in February 2017, the mission was developed in a joint partnership between Goddard Space Flight Center (GSFC) and an international consortium from the United States, United Kingdom, and Italy. The mission is operated by Pennsylvania State University as part of NASA's Medium Explorer program (MIDEX).

<span class="mw-page-title-main">High Energy Astronomy Observatory 1</span> X-ray telescope launched in 1977

HEAO-1 was an X-ray telescope launched in 1977. HEAO-1 surveyed the sky in the X-ray portion of the electromagnetic spectrum, providing nearly constant monitoring of X-ray sources near the ecliptic poles and more detailed studies of a number of objects by observations lasting 3–6 hours. It was the first of NASA's three High Energy Astronomy Observatories, HEAO 1, launched August 12, 1977 aboard an Atlas rocket with a Centaur upper stage, operated until 9 January 1979. During that time, it scanned the X-ray sky almost three times

<span class="mw-page-title-main">INTEGRAL</span> European space telescope for observing gamma rays

The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a 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 observatory in space. 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 and HESS.

<span class="mw-page-title-main">Gamma-ray Burst Coordinates Network</span>

The gamma-ray burst coordinates network (GCN) is a system that distributes information about the location of a gamma-ray burst (GRB), called notices, when a burst is detected by various spacecraft. The GCN also automatically receives and distributes messages, called circulars, about follow-up observations to interested individuals and institutions. Follow-up observations may be made by ground-based and space-based optical, radio, and X-ray observatories.

The InterPlanetary Network (IPN) is a group of spacecraft equipped with gamma ray burst (GRB) detectors. By timing the arrival of a burst at several spacecraft, its precise location can be found. The precision for determining the direction of a GRB in the sky is improved by increasing the spacing of the detectors, and also by more accurate timing of the reception. Typical spacecraft baselines of about one AU and time resolutions of tens of milliseconds can determine a burst location within several arcminutes, allowing follow-up observations with other telescopes.

<span class="mw-page-title-main">Granat</span> 1989 Soviet space observatory

The International Astrophysical Observatory "GRANAT", was a Soviet space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations. It operated for almost nine years.

Gamma was a Soviet gamma ray telescope. It was launched on 11 July 1990 into an orbit around Earth with a height of 375 km and an inclination of 51.6 degrees. It lasted for around 2 years. On board the mission were three telescopes, all of which could be pointed at the same source. The project was a joint Soviet-French project.

The history of gamma-ray began with the serendipitous detection of a gamma-ray burst (GRB) on July 2, 1967, by the U.S. Vela satellites. After these satellites detected fifteen other GRBs, Ray Klebesadel of the Los Alamos National Laboratory published the first paper on the subject, Observations of Gamma-Ray Bursts of Cosmic Origin. As more and more research was done on these mysterious events, hundreds of models were developed in an attempt to explain their origins.

OSO 7

OSO 7 or Orbiting Solar Observatory 7, before launch known as OSO H is the seventh in the series of American Orbiting Solar Observatory satellites launched by NASA between 1962 and 1975. OSO 7 was launched from Cape Kennedy on 29 September 1971 by a Delta N rocket into a 33.1° inclination, low-Earth orbit, and re-entered the Earth's atmosphere on 9 July 1974. It was built by the Ball Brothers Research Corporation (BBRC), now known as Ball Aerospace, in Boulder Colorado.

<span class="mw-page-title-main">Gamma-ray astronomy</span> Observational astronomy performed with gamma rays

Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic form of electromagnetic radiation, with photon energies above 100 keV. Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy.

X-ray emission occurs from many celestial objects. These emissions can have a pattern, occur intermittently, or as a transient astronomical event. In X-ray astronomy many sources have been discovered by placing an X-ray detector above the Earth's atmosphere. Often, the first X-ray source discovered in many constellations is an X-ray transient. These objects show changing levels of X-ray emission. NRL astronomer Dr. Joseph Lazio stated: " ... the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, ...". There are a growing number of recurrent X-ray transients. In the sense of traveling as a transient, the only stellar X-ray source that does not belong to a constellation is the Sun. As seen from Earth, the Sun moves from west to east along the ecliptic, passing over the course of one year through the twelve constellations of the Zodiac, and Ophiuchus.

<span class="mw-page-title-main">X-ray astronomy satellite</span> Satellite involved in X-ray astronomy

An X-ray astronomy satellite studies X-ray emissions from celestial objects, as part of a branch of space science known as X-ray astronomy. Satellites are needed because X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites.

X-ray astronomy detector

X-ray astronomy detectors are instruments that detect X-rays for use in the study of X-ray astronomy.

<span class="mw-page-title-main">Gerald J. Fishman</span> American astronomer

Gerald Jay (Jerry) Fishman is an American research astrophysicist, specializing in gamma-ray astronomy. His research interests also include space and nuclear instrumentation and radiation in space. A native of St. Louis, Missouri, Fishman obtained a B.S. with Honors degree in Physics from the University of Missouri in 1965, followed by M.S. and Ph.D. degrees in Space Science from Rice University in 1968 and 1970, respectively.

References

  1. "NASA – NSSDCA – Spacecraft – Details". nssdc.gsfc.nasa.gov. Retrieved 2018-04-30.
  2. "NASA – NSSDCA – Spacecraft – Trajectory Details". nssdc.gsfc.nasa.gov. Retrieved 2018-04-30.
  3. "Gamma-Ray Astronomy in the Compton Era: The Instruments". Gamma-Ray Astronomy in the Compton Era. NASA/ GSFC. Archived from the original on 2009-02-24. Retrieved 2007-12-07.
  4. 1 2 "Spaceflight Now | CGRO Deorbit | NASA space telescope heads for fiery crash into Pacific". spaceflightnow.com.
  5. Barry Logan : MSFC, Kathy Forsythe : MSFC. "NASA – NASA's Great Observatories". www.nasa.gov.
  6. BATSE GUEST INVESTIGATOR PROGRAM
  7. "CGRO SSC >> EGRET Detection of Gamma Rays from the Moon". heasarc.gsfc.nasa.gov.
  8. NASA Preparing Plans for Destructive Reentry to End Compton Gamma Ray Observatory's Mission Cowling. Jan 2000
  9. March 1994 - Gamma Ray Observatory Remote Terminal System (GRTS) Declared Operational
  10. 1 2 3 "CGRO SSC >> Successful Reboost of Compton Gamma Ray Observatory". heasarc.gsfc.nasa.gov.
  11. "Satellite Marked for Extinction Plunges Into the Sea, on Target (Published 2000)". The New York Times. Associated Press. June 5, 2000.
  12. "Entry Debris Field estimation methods and application to Compton Gamma Ray Observatory" (PDF). Mission Operations Directorate Nasa Johnson Space Center.