Fermi Gamma-ray Space Telescope - Overview

Overview

Fermi 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 to 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 8 keV to 1 MeV range and two bismuth germanate crystals with sensitivity from 150 keV to 30 MeV), and can detect gamma-ray bursts in that energy range across the whole of the sky not occluded by the Earth.

General Dynamics Advanced Information Systems (formerly Spectrum Astro and now Orbital Sciences) in Gilbert, Arizona designed and built the spacecraft that carries the instruments. It travels in a low, circular orbit with a period of about 95 minutes. Its normal mode of operation maintains 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 are available to the public through the Fermi Science Support Center web site. Software for analyzing the data is also available.