These admitted rays then strike a thin tungsten sheet that cleaves them into an electron and a positron (a twin electron, but with a positive charge). Next, a series of silicon chip layers track the path of the particle pairs to pinpoint the source of the rays. The particles finally strike a so-called calorimeter, a device made of cesium iodide that measures the energy of the ray captured by the orbiting observatory.
After GLAST launches, mission controllers will spend a couple of weeks slowly turning on and fine-tuning its instruments and sensors, followed by a month or so to make sure they are properly interpreting the data from LAT, the main telescope. Researchers should be able to monitor gamma-ray bursts almost immediately after GLAST comes online by using its second instrument, called the GLAST burst monitor (GBM). Made up of flat disks of sodium iodide, the GBM looks for brief, less energetic pulses that are much easier to interpret because they come on fast and fade equally quickly. These less intense, though nonetheless powerful, pulses will include gamma rays from within our own galaxy as well as those emitted by our sun. GBM will also view the entire sky—except for the pocket blocked by Earth.
GLAST is slated to scan the heavens for gamma rays for five years, but researchers hope the satellite may peer across the universe for a full decade. With each pass of the sky, astronomers hope to gather more information about faraway, gamma-bright objects, watching them evolve as their gamma-ray emissions change over time.
"Though we will be surveying the whole sky," Ritz says, "it's like we will be zooming in more with each orbit."