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Fermi Gamma-ray Space Telescope

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 GLAST, the GLAST Burst Monitor (GBM), is being used to study gamma ray bursts.

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. 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.

Overview

GLAST includes two scientific instruments, the Large Area Telescope (LAT) and the GLAST 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. The GBM was constructed at the University of California at Santa Cruz UCSC.

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.

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

Mission

The key scientific objectives of the GLAST mission are:

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 (eg. 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].

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

Mission Status

Prelaunch

On 2008-03-04 the spacecraft arrived at the Astrotech payload processing facility in Titusville, Florida. On 2008-06-04, after several previous delays, launch status was retargeted for June 11 at the earliest, the last delays resulting from the need to replace the Flight Termination System batteries.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.

Launch

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 Launch Complex 17 aboard a Delta 7920H-10C rocket.

Orbit

GLAST resides in a low-earth circular orbit at an altitude of , and at an inclination of 28.5 degrees.

Software modifications

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

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.

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).

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."

GBM

GBM is an acronym for 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.

GBM Participating Institutions

US Team Institution

NASA's Marshall Space Flight Center

German Team Institution

Max Planck Institut für Extraterrestrische Physik

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 microstrips, 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 may be 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).

LAT Participating Institutions

US Team Institutions

Stanford University, Physics Department, GLAST group & Hansen Experimental Physics Laboratory
Stanford Linear Accelerator Center, Particle Astrophysics group
NASA Goddard Space Flight Center, Astrophysics Science Division
U.S. Naval Research Laboratory, High Energy Space Environment (HESE) branch
Ohio State University, Physics Department
University of California, Santa Cruz, Physics Department
Sonoma State University, Department of Physics & Astronomy
University of Washington
Texas A&M University-Kingsville

Japanese Team Institutions

Italian Team Institutions

Instituto Nazionale di Fisica Nucleare (INFN)
Italian Space Agency
Istituto di Fisica Cosmica, Milano, CNR
INFN and University of Bari
INFN and University of Padova
INFN and University of Perugia
INFN and University of Pisa
INFN and University of Rome Tor Vergata
INFN and University of Trieste
INFN and University of Udine

French Team Institutions

Service d'Astrophysique, CEA DAPNIA, CEA Saclay
Centre National d'Études Spatiales
Institut National de Physique Nucléaire et de Physique des Particules, IN2P3
Laboratoire Leprince-Ringuet de l'École Polytechnique
Centre d'Études nucléaires de Bordeaux Gradignan
Laboratoire de Physique Théorique et Astroparticules, Montpellier

Swedish Team Institutions

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.