Celebrating 10 Years of the Fermi Gamma-Ray Space Telescope
Ten years ago today, NASA's Fermi Gamma-ray Space Telescope was launched on a Delta II Heavy Launch Vehicle. Originally named GLAST (Gamma-Ray Large Area Space Telescope) the spacecraft was launched with two instruments - Large Area Telescope (LAT) and GLAST burst monitor (GBM).
The LAT detects gamma rays by using Einstein’s famous E = mc2 equation in a technique known as pair production. When a gamma ray, which is pure energy, slams into a layer of tungsten in the detector, it can create a pair of subatomic particles (an electron and its antimatter counterpart, a positron). The direction of the incoming gamma ray is determined by projecting the direction of these particles back to their source using several layers of high-precision silicon tracking detectors. A separate detector, called a calorimeter, absorbs and measures the energy of the particles. Since the energy of the particles created depends on the energy of the original gamma ray, counting up the total energy determines the energy of that gamma ray. Becausethe LAT in orbit is bombarded by many more particles than gamma rays, it wears a “hat” – a third detector that produces a signal when a particle, but not a gamma ray, goes through it. The combination of no signal in this outer detector (“the dog that did not bark”), plus an electron- positron pair of tracks created inside the LAT, signals a gamma ray. Working one gamma ray at a time, the LAT makes gamma-ray images of astronomical objects, while also determining the energy for each detected gamma ray.
The GLAST Burst Monitor (GBM) was selected as a complementary instrument for the GLAST mission is sensitive to X rays and gamma rays with energies between 8 keV and 30 MeV.
Here is a short video celebrating 5 achievements the satellite has contributed to:
Source : NASA