By Jonathan Dorfan
GLASTing into Space
Twenty-two months from now, the GLAST satellite, a complicated and
sturdy set of particle physics detectors,
will be encapsulated into the cone of
a Delta 2 Heavy rocket at Kennedy
Space Center, and blasted into space. A
crew of SLAC engineers and physicists
will crane their necks and shield their
eyes, looking on in pride as their
painstaking work takes flight. They will
be accompanied by an equally excited
and exhilarated group of collaborators
from the rest of the U.S., and around the
(Photo by Diana Rogers)
Once in orbit around the Earth, the entire
GLAST observatory, including the Large
Area Telescope (LAT) detector assembled and tested at SLAC, will come
from the rocket and will begin its primary mission: surveying the entire
every two orbits encoding the energy, arrival time and directions of
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
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
different stories and reflect different extra-terrestrial phenomena.
rays can be emissaries from the oldest and farthest reaches of the
expect to learn more about black holes, supersymmetric dark matter,
gravity, pulsars, and understand how gamma rays are accelerated and how
GLAST is an international collaboration funded by NASA, the
of Energy, and government agencies in Italy, France, Japan and Sweden.
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.