Rendering of the GLAST spacecraft

Image courtesy of NASA

The next major space observatory, the Gamma-ray Large Area Space Telescope (GLAST), is about to begin gathering new information about subatomic particles, black holes, and the birth and evolution of the universe. The launch from Cape Canaveral is planned for Wednesday, June 11th.

GLAST, designed with important participation from scientists at the Stanford Linear Accelerator Center and main campus, will study the most energetic particles of light, observing physical processes far beyond the capabilities of earthbound laboratories.

GLAST's main instrument, the Large Area Telescope (LAT), operates more like a particle detector than a conventional telescope. From within its 1.8-meter cube housing, the LAT will use 880,000 silicon strips to detect high-energy gamma rays with unprecedented resolution and sensitivity, filling in gaps in understanding left by previous missions, and pushing new boundaries in particle physics and astrophysics.

The Stanford Linear Accelerator Center (SLAC) managed the development of the LAT and integrated the instrument from hardware fabricated at laboratories around the world. SLAC also runs the Instrument Science Operations Center (ISOC), which will process the LAT data for the duration of the mission. The total U.S. cost of the LAT is $196 million, of which the U.S. Department of Energy (DOE) contributed $45 million for LAT fabrication; the DOE also supported LAT researchers and the ISOC facilities and staff.

As GLAST orbits Earth, gamma rays­emanating from jets of plasma streaming from enormous black holes, pulsars, and other astronomical sources­will first encounter several layers of tungsten metal in the LAT. The high-energy gamma rays will interact with tungsten's massive and highly charged atomic nuclei in a way that creates pairs of charged particles: one electron and one positron. These particles will then be detected by silicon-strip sensors positioned just below each tungsten layer. Later, these signals will be used to reconstruct the direction and arrival time of the original gamma-ray photon.

After traversing through the LAT's tracking layers, the particles will pass into a cesium iodide imaging calorimeter, where they will generate tiny amounts of light­flashes with brightness proportional to the particles' energies.

This multi-step process makes the LAT at least 30 times more sensitive than any previous satellite detector and will allow it to survey the entire sky several times per day. Physicists and astronomers expect that this unprecedented look at the gamma-ray sky will reveal vital information about subatomic particles at energies far greater than those seen in ground-based particle accelerators, about the accelerating powers of supermassive black holes, and about the birth and evolution of the universe.

GLAST will also carry a smaller instrument, called the GLAST Burst Monitor (GBM), to detect gamma-ray bursts and other transient phenomena. Together with the LAT, the GBM will enable GLAST to make gamma-ray burst observations spanning a factor of ten million in energy. GLAST is planned for a five-year primary mission operating phase, which may be extended for up to ten years.