GLASTing into Space

Once in orbit around the Earth, the entire GLAST observatory, including the Large Area Telescope (LAT) detector assembled and tested at SLAC, will come free from the rocket and will begin its primary mission: surveying the entire sky every two orbits encoding the energy, arrival time and directions of gamma rays. Orbiting well above the earth’s dense atmosphere, the gamma rays are detected with high precision.

Gamma rays are photons, as are x-rays, sunlight and microwaves, but with a lot more energy. The LAT will identify the energy and direction of gamma rays with energies from 10 MeV to 300 GeV. To get a sense of how extremely energetic these particles are, remember that the linac accelerates particles to 50 GeV.

The observatory will take a picture of the gamma-ray sky, which will look quite different than what we see when we look at the heavens. What our eyes see is low energy visible light. The two pictures of the heavens tell very different stories and reflect different extra-terrestrial phenomena. Gamma rays can be emissaries from the oldest and farthest reaches of the universe. We expect to learn more about black holes, supersymmetric dark matter, quantum gravity, pulsars, and understand how gamma rays are accelerated and how they behave.

GLAST is an international collaboration funded by NASA, the Department of Energy, and government agencies in Italy, France, Japan and Sweden. The observatory consists of two scientific instruments, LAT and the GLAST Burst Monitor (GBM). INFN in Italy, in collaboration with Japan and the U.S., built the 16 towers for LAT that collectively make up the tracker detector. These were mounted into the aluminum support frame along with the calorimeter modules which were built as a collaboration of the U.S., France and Sweden. SLAC integrated the tracker towers and the calorimeters with electronics, trigger and data flow systems. This week the team at SLAC covered these central elements with the Anti-Coincidence Detector, which identifies the many incoming particles that are not gammas, and are therefore not of interest.

I am delighted that so many of you went to the GLAST open house on Oct. 26 to take a last look at the tracker through the clean-room windows.

In January, SLAC will send the completed LAT to the Naval Research Laboratory for flight testing. The LAT instrument will be shaken, put under vacuum, heated and cooled to extreme temperatures, and blasted with noise, all to simulate launch and space conditions to make sure the instrument is flight-qualified. SLAC has already tested each individual module of LAT in these ways.

After GLAST successfully reaches space, SLAC will continue to play an important role. The observatory’s data will be relayed to NASA and then sent to the Instrument Science Operating Center (ISOC) at SLAC. This new center will occupy part of the Central Lab Annex. ISOC staff will monitor the health and safety of the instrument, create commands to operate it, and process the raw data so researchers can use it.

In the first year of operation, the GLAST collaboration will analyze the gamma-ray sky, how it changes on a daily basis, trying to understand what happens around black holes, what dark matter is, and other key questions in 21st century particle astrophysics. GLAST represents a true merging and collaboration of particle physics and particle astrophysics, with particle physics detectors launched into space to answer questions by watching the most powerful particle accelerators in our universe. Exciting times are ahead for all of us.