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.

The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden,[6] becoming the most sensitive gamma-ray telescope on orbit, succeeding INTEGRAL.

[7][8] Fermi includes two scientific instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM).

General Dynamics Advanced Information Systems (formerly Spectrum Astro and now Orbital Sciences) in Gilbert, Arizona, designed and built the spacecraft that carries the instruments.

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.

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.

The LAT high voltage was turned on 25 June, and it began detecting high-energy particles from space, but minor adjustments were still needed to calibrate the instrument.

On 3 April, telescope operators decided to stow the satellite's high-gain parabolic antenna, rotate the solar panels out of the way and to fire Fermi's rocket thrusters for one second to move it out of the way.

The improvement in the performance of Fermi LAT due to Pass 8 is so dramatic that this software update is sometimes called the cheapest satellite upgrade in history.

This anisotropy was traced to cosmic-ray electrons leaking through the ribbons of the Anti-Coincidence Detector and a set of cuts allowed rejection of these events while minimally impacting acceptance.

[46] On 16 March 2018 one of Fermi's solar arrays quit rotating, prompting a transition to "safe hold" mode and instrument power off.

[47] 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, the first of its kind.

[50] The explosion had the power of about 9,000 ordinary supernovae, and the relativistic jet of material ejected in the blast must have moved at a minimum of 99.9999% the speed of light.

[51] In 2009, a surplus of gamma rays from a spherical region around the Galactic Center of the Milky Way was found in data from the Fermi telescope.

Possibilities include star forming galaxies, galactic mergers, and yet-to-be explained dark matter interactions.

[56] The galaxy's diffuse gamma-ray fog hampered prior observations, but the discovery team led by D. Finkbeiner, building on research by G. Dobler, worked around this problem.

Avi Loeb has theorised that if a massive star is rapidly rotating, the centrifugal force produced during its collapse will lead to the formation of a rotating bar that breaks into two dense clumps of matter with a dumbbell configuration that becomes a black hole binary, and at the end of the star's collapse it triggers a gamma-ray burst.

[69][70] Loeb suggests that the 0.4 second delay is the time it took the gamma-ray burst to cross the star, relative to the gravitational waves.

Six minutes later, a single detector at Hanford LIGO registered a gravitational-wave candidate which was consistent with a binary neutron star merger, occurring 2 seconds before the GRB 170817A event.

The design is optimized for good resolution in time and photon energy, and is sensitive from 8 keV (a medium X-ray) to 40 MeV (a medium-energy gamma-ray).

[58] The Large Area Telescope (LAT) detects individual gamma rays using technology similar to that used in terrestrial particle accelerators.

The 2011 Bruno Rossi Prize was awarded to Bill Atwood, Peter Michelson and the Fermi LAT team "for enabling, through the development of the Large Area Telescope, new insights into neutron stars, supernova remnants, cosmic rays, binary systems, active galactic nuclei and gamma-ray bursts.

[75] The 2014 prize went to Tracy Slatyer, Douglas Finkeiner and Meng Su "for their discovery, in gamma rays, of the large unanticipated Galactic structure called the Fermi bubbles.

"[76] The 2018 prize was awarded to Colleen Wilson-Hodge and the Fermi GBM team for the detection of GRB 170817A, the first unambiguous and completely independent discovery of an electromagnetic counterpart to a gravitational wave signal (GW170817) that "confirmed that short gamma-ray bursts are produced by binary neutron star mergers and enabled a global multi-wavelength follow-up campaign.