Fermi Gamma-ray Space Telescope

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Fermi Gamma-ray Space Telescope (GLAST)

The GLAST instrument after arriving at Cape Canaveral in May 2008
General information
Organization NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.
Major contractors General Dynamics
Launch date 11 June 2008, 16:05 UTC
Launched from Cape Canaveral Air Force Station Space Launch Complex 17, Launch Pad B
Launch vehicle Delta II 7920-H rocket
Mission length 1 year and 29 days elapsed
Orbit height 550 km (340 mi)
Orbit period about 95 minutes
Wavelength gamma ray
Instruments
Large Area Telescope (LAT) telescope
Website glast.gsfc.nasa.gov
Artist's conception of GLAST in orbit

The Fermi Gamma-ray Space Telescope (formerly named the Gamma-ray Large Area Space Telescope, or 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 (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts.[1]

GLAST was launched 2008-06-11 at 16:05 GMT aboard a Delta II 7920-H rocket. The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.[2] NASA announced 2008-02-08 that it was seeking a new name that would, "capture the excitement of GLAST's mission and call attention to gamma-ray and high-energy astronomy."[3]

Contents

[edit] Overview

GLAST includes two scientific instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The LAT is an imaging gamma-ray detector (a pair-conversion instrument) which detects photons with energy from about 30 million to about 300 billion electron volts (30 MeV - 300 GeV), with a field of view of about 20% of the sky; it may be thought of as a sequel to the EGRET instrument on the Compton gamma ray observatory. The GBM consists of 14 scintillation detectors (twelve sodium iodide crystals for the 8keV to 1MeV range and two bismuth germanate crystals with sensitivity from 150keV to 30MeV), and can detect gamma-ray bursts in that energy range across the whole of the sky not occulted by the Earth.

Fermi G.S.T. logo

General Dynamics Advanced Information Systems (formerly Spectrum Astro) in Gilbert, Arizona designed and built the spacecraft that carries the instruments. It will travel in a low, circular orbit with a period of about 95 minutes. Its normal mode of operation will maintain its orientation so that the instruments will look away from the earth, with a "rocking" motion to equalize the coverage of the sky. The view of the instruments will sweep out across most of the sky about 16 times per day. The spacecraft can also maintain an orientation that points to a chosen target.

Both science instruments underwent environmental testing, including vibration, vacuum, and high and low temperatures to ensure that they can withstand the stresses of launch and continue to operate in space. They were integrated with the spacecraft at the General Dynamics ASCENT facility in Gilbert, Arizona.

Data from the instruments will be available to the public through the GLAST Science Support Center web site. Software for analyzing the data will also be available. Scientists with plans for research will be able to apply to the Guest Investigator program.

NASA's Alan Stern, associate administrator for Science at NASA Headquarters, launched a public competition 2008-02-07, closing 2008-03-31, to rename GLAST in a way that would "capture the excitement of GLAST’s mission and call attention to gamma-ray and high-energy astronomy... something memorable to commemorate this spectacular new astronomy mission... a name that is catchy, easy to say and will help make the satellite and its mission a topic of dinner table and classroom discussion."[4]

On 2008-08-26, GLAST was renamed the "Fermi Gamma-ray Space Telescope" in honor of Enrico Fermi, a pioneer in high-energy physics.[5]

[edit] Mission

Anticipated GLAST operations timeline.

NASA designed the mission with a five-year lifetime, with a goal of ten years of operations.[6]

The key scientific objectives of the GLAST mission have been described as:[7]

  • To understand the mechanisms of particle acceleration in active galactic nuclei (AGN), pulsars, and supernova remnants (SNR).
  • Resolve the gamma-ray sky: unidentified sources and diffuse emission.
  • Determine the high-energy behavior of gamma-ray bursts and transients.
  • Probe dark matter (e.g. by looking for an excess of gamma rays from the center of the Milky Way) and early Universe.
  • Search for evaporating primordial micro black holes (MBH) from their presumed gamma burst signatures [Hawking Radiation component].

However the National Academies of Sciences ranked this mission as a top priority.[8] Many new possibilities and discoveries are anticipated to emerge from this single mission and greatly expand our view of the Universe:[8][9]

Study energy spectra and variability of wavelengths of light coming from blazars so as to determine the composition of the black hole jets aimed directly at Earth -- whether they are
(a) a combination of electrons and positrons or
(b) only protons.
Study gamma-ray bursts with an energy range several times more intense than ever before so that scientists may be able to understand them better.
Study younger, more energetic pulsars in the Milky Way than ever before so as to broaden our understanding of stars. Study the pulsed emissions of magnetospheres so as to possibly solve how they are produced. Study how pulsars generate winds of interstellar particles.
Study better than ever before whether supernova remnants are responsible for the accelerations of interstellar subatomic particles.
Provide new data to help improve upon existing theoretical models of our own galaxy.
Study better than ever before whether active galactic nuclei and ordinary galaxies are responsible for gamma-ray background radiation. The potential for a tremendous discovery awaits if those sources are determined to be irresponsible, in which case the cause may be anything from self-annihilating dark matter to entirely new chain reactions among intersellar particles that have yet to be conceived.
Study better than ever before how concentrations of visible and ultraviolet light change over time. The mission should easily detect E=mc2 working in reverse, where energy was actually converted into mass, in the early universe.
Study better than ever before how our own Sun produces gamma rays in solar flares.
Search for evidence that dark matter is comprised of weakly interacting massive particles, complementing similar experiments already planned for the Large Hadron Collider as well as other underground detectors. The potential for a tremendous discovery in this area is possible over the next several years.
Test better than ever before certain established theories of physics, such as whether the speed of light in vacuum remains constant regardless of wavelength. Einstein's general theory of relativity contends that it does, yet some models in quantum mechanics and quantum gravity predict that it may not. Search for gamma rays emanating from former black holes that once exploded, providing yet another potential step toward the unification of quantum mechanics and general relativity. Determine whether photons naturally split into smaller photons, as predicted by quantum mechanics and already achieved under controlled, man-made experimental conditions.
  • Unknown discoveries[20]
Scientists estimate a very high possibility for new scientific discoveries, even revolutionary discoveries, emerging from this single mission.

[edit] Mission Status

[edit] Prelaunch

On 2008-03-04 the spacecraft arrived at the Astrotech payload processing facility in Titusville, Florida.[21] On 2008-06-04, after several previous delays, launch status was retargeted for June 11 at the earliest,[22][23] the last delays resulting from the need to replace the Flight Termination System batteries.[24] The launch window extended from 11:45 a.m. until 1:40 p.m. EDT (15:45-17:40 GMT) daily, until 2008-08-07.[24]

[edit] Launch

GLAST launch aboard a Delta II rocket, 11 June 2008.

Launch occurred successfully on 2008-06-11 at 16:05, and the spacecraft separated from the carrier rocket about 75 minutes later. The spacecraft departed from pad B at Cape Canaveral Air Force Station Space Launch Complex 17 aboard a Delta 7920H-10C rocket.

[edit] Orbit

GLAST resides in a low-earth circular orbit at an altitude of 550 km (340 mi), and at an inclination of 28.5 degrees.[25]

[edit] Software modifications

GLAST received some minor modifications to its computer software 2008-06-23.

[edit] LAT/GBM computers operational

Computers operating both the LAT and GBM (see below) and most of the LAT's components were turned on, 2008-06-24. The LAT high voltage was turned on, 2008-06-25, and it began detecting high-energy particles from space, but minor adjustments were still needed to calibrate the instrument. The GBM high voltage was also turned on, 2008-06-25, but the GBM was still requiring one more week of testing/calibrations before searching for gamma-ray bursts.

[edit] Sky Survey Mode

GLAST was expected to have switched to "sky survey mode" on 2008-06-26 so as to begin sweeping its field of view over the entire sky every three hours (every two orbits).

[edit] Discoveries

Gamma-ray pulsars detected by the Fermi Gamma-ray Space Telescope.
Cycle of pulsed gamma rays from the Vela pulsar. Constructed from photons detected by Fermi's Large Area Telescope.

The first major discovery came when the space telescope detected a pulsar in the CTA 1 supernova remnant that appeared to emit radiation in the gamma ray bands only, a first for its kind.[26]

This new pulsar sweeps the earth every 316.86 milliseconds and is about 4,600 light years away.[27]

The gamma-ray burst GRB 080916C in the constellation Carina, which occurred in September 2008 and recorded by the telescope has been confirmed to have "the greatest total energy, the fastest motions, and the highest-energy initial emissions" ever seen. The explosion had the power of about 9,000 ordinary supernovae, and the gas bullets emitting the initial gamma rays must have moved at 99.9999 percent the speed of light. The tremendous power and speed make this blast the most extreme recorded to date.[28]

[edit] GLAST Science Packages

After presenting an overview of the GLAST instrumentation and goals, Jennifer Carson of the Stanford Linear Accelerator Center concludes that the primary goals "are all achievable with the all-sky scanning mode of observing."[29]

[edit] GBM

GBM is an acronym for Gamma-ray Burst Monitor (formerly GLAST Burst Monitor); the GBM detects sudden flares of gamma-rays produced by gamma ray bursts and solar flares. Its scintillators are on the sides of the spacecraft to view all of the sky which is not blocked by the earth. The design is optimized for good resolution in time and photon energy.

"Gamma-ray bursts are so bright we can see them from billions of light years away, which means they occurred billions of years ago, and we see them as they looked then," says Charles Meegan of NASA's Marshall Space Flight Center.[30]

[edit] GBM Participating Institutions

[edit] US Team Institution

[edit] German Team Institution

[edit] LAT

LAT is an acronym for Large Area Telescope; the LAT detects individual gamma rays using technology similar to that used in terrestrial particle accelerators. Photons hit thin metal sheets, converting to electron-positron pairs, via a process known as pair production. These charged particles pass through interleaved layers of silicon microstrip detectors, causing ionization which produce detectable tiny pulses of electric charge. Researchers can combine information from several layers of this tracker to determine the path of the particles. After passing through the tracker, the particles enter the calorimeter, which consists of a stack of caesium iodide scintillator crystals to measure the total energy of the particles. The LAT's field of view is large, about 20% of the sky. The resolution of its images is modest by astronomical standards, a few arc minutes for the highest-energy photons and about 3 degrees at 100 MeV. The LAT is a bigger and better successor to the EGRET instrument on NASA's Compton Gamma Ray Observatory satellite in the 1990s. Several countries produced the components of the LAT, who then sent the components for assembly at the Stanford Linear Accelerator Center (SLAC).

[edit] LAT Participating Institutions

[edit] US Team Institutions

[edit] Japanese Team Institutions

[edit] Italian Team Institutions

[edit] French Team Institutions

[edit] Swedish Team Institutions

[edit] Education and public outreach

Education and public outreach are important components of the GLAST project. The main GLAST education and public outreach website at http://glast.sonoma.edu offers gateways to resources for students, educators, scientists, and the public. NASA’s Education and Public Outreach (E/PO) group operates the GLAST education and outreach resources at Sonoma State University.

[edit] References

  1. ^ "NASA's GLAST Burst Monitor Team Hard at Work Fine-Tuning Instrument and Operations". NASA. 2008-07-28. http://www.nasa.gov/mission_pages/GLAST/news/glast_gbm.html. 
  2. ^ "An Astro-Particle Physics Partnership Exploring the High Energy Universe - List of funders". SLAC. http://glast.stanford.edu/. Retrieved on August 9, 2007. 
  3. ^ "Name that Space Telescope!". NASA. 2008-02-08. http://science.nasa.gov/headlines/y2008/08feb_namethattelescope.htm. 
  4. ^ "NASA Calls for Suggestions to Re-Name Future Telescope Mission". NASA. 2008-02-07. http://www.nasa.gov/home/hqnews/2008/feb/HQ_08036_GLAST.html. Retrieved on 2008-02-10. 
  5. ^ "First Light for the Fermi Space Telescope". NASA. 2008-08-26. http://science.nasa.gov/headlines/y2008/26aug_firstlight.htm. 
  6. ^ "The GLAST Mission - GLAST Overview, mission length". NASA. http://glast.gsfc.nasa.gov/public/. Retrieved on August 9, 2007. 
  7. ^ "The Mission". SLAC. http://glast.stanford.edu/mission.html. Retrieved on August 9, 2007. 
  8. ^ a b "[http://www.nasa.gov/mission_pages/GLAST/main/questions_answers.html NASA - Q&A ON THE GLAST MISSION]". Nasa: Fermi Gamma-ray Space Telescope. NASA. 28 August 2008. http://www.nasa.gov/mission_pages/GLAST/main/questions_answers.html. Retrieved on 29 April 2009. 
  9. ^ See also Nasa - Fermi Science and NASA - Scientists Predict Major Discoveries for GLAST.
  10. ^ http://www.nasa.gov/mission_pages/GLAST/science/blazers.html
  11. ^ http://www.nasa.gov/mission_pages/GLAST/science/gammay_ray_bursts.html
  12. ^ http://www.nasa.gov/mission_pages/GLAST/science/neutron_stars.html
  13. ^ http://www.nasa.gov/mission_pages/GLAST/science/cosmic_rays.html
  14. ^ http://www.nasa.gov/mission_pages/GLAST/science/milky_way_galaxy.html
  15. ^ http://www.nasa.gov/mission_pages/GLAST/science/gamma_ray_background.html
  16. ^ http://www.nasa.gov/mission_pages/GLAST/science/early_universe.html
  17. ^ http://www.nasa.gov/mission_pages/GLAST/science/solar_system.html
  18. ^ http://www.nasa.gov/mission_pages/GLAST/science/dark_matter.html
  19. ^ http://www.nasa.gov/mission_pages/GLAST/science/testing_fundamental_physics.html
  20. ^ http://www.nasa.gov/mission_pages/GLAST/science/unidentified_sources.html
  21. ^ "GLAST Spacecraft Arrives in Florida to Prepare for Launch". NASA. http://www.nasa.gov/centers/kennedy/news/releases/2008/release-20080304.html. 
  22. ^ "Spaceflight Now - Tracking Station - Worldwide launch schedule". http://www.spaceflightnow.com/tracking/index.html. Retrieved on 2008-06-04. 
  23. ^ "GLAST Mission Coverage - Latest News". http://www.nasa.gov/mission_pages/GLAST/main/index.html. Retrieved on 2008-06-04. 
  24. ^ a b "NASA - Expendable Launch Vehicle Status Report". NASA. 2008-06-06. http://www.nasa.gov/centers/kennedy/launchingrockets/status/2008/elvstatus-20080606.html. Retrieved on 2008-06-09. 
  25. ^ "The GLAST Mission - GLAST Overview, orbital information". NASA. http://glast.gsfc.nasa.gov/public/. Retrieved on August 9, 2007. 
  26. ^ http://www.universetoday.com/2008/10/17/fermi-telescope-makes-first-big-discovery-gamma-ray-pulsar/
  27. ^ Cosmos Online - New kind of pulsar discovered (http://www.cosmosmagazine.com/news/2260/new-kind-pulsar-discovered)
  28. ^ Most Extreme Gamma-ray Blast Ever, Seen By Fermi Gamma-ray Space Telescope, Science Daily, February 19, 2009
  29. ^ Carson, Jennifer. "GLAST: physics goals and instrument status". http://arxiv.org/pdf/astro-ph/0610960. 
  30. ^ "GLAST Off!". NASA. http://science.nasa.gov/headlines/y2008/11jun_glast2.htm. 

[edit] External links

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