NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

Large Area Telescope (LAT)

NSSDCA ID: 2008-029A-01

Mission Name: Fermi Gamma-ray Space Telescope
Principal Investigator:Prof. Peter F. Michelson


LAT is an array of 4 x 4 "towers". Each tower carries an anti-coincidence screen, backed by 19 layers of thin tungsten sheets and 19 layers of position-sensitive silicon strips, with one set of strips along the "x-direction" and the other in the "y-direction". The strip layers and the tungsten sheets alternate. Finally, there is the cesium iodide (CsI) calorimeter to measure the total energy by means of its light flash. The anti-coincidence sheet is made of a plastic that does not flash when a gamma-ray enters, but does when a charged cosmic ray enters. These cosmic rays are a million-fold more numerous than the gamma-rays, so must be rejected thoroughly, by the coincidence of the light flashes from that screen and the calorimeters. The purpose of the tungsten layer is to convert the gamma-rays into an electron-positron pair, so that each of them can be tracked by the position sensitive x-y strips.

The instrument covers gamma-rays in the energy band 30 MeV to 300 GeV, and can pinpoint the direction of arrival with a precision of an arc-minute.

Alternate Names

  • Fermi/LAT
  • LAT


  • Astronomy: Gamma Ray

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Prof. Peter F. MichelsonPrincipal InvestigatorStanford University
[] NASA Logo -