One of the major goals of the ongoing space shuttle mission—Endeavour's final visit to the International Space Station—was to bestow a 7.8-ton parting gift: an automated particle detector called the Alpha Magnetic Spectrometer (AMS-02, or, more colloquially, AMS), which was attached to the station yesterday. Each second, the AMS will encounter 25,000 cosmic rays—high-speed atomic and subatomic particles (some from the sun, some from deep space), the most energetic of which pack hundreds of times as much energy as anything a scientist can whip up in an Earth-based particle accelerator. The 650 computers in the instrument will track the particles’ trajectory, speed, and energy, which the device’s designers hope will provide insights into mysterious forms of matter, including antimatter, dark matter, and a hypothetical family of particles called strangelets.
When a particle enters the AMS, it passes through a gauntlet of experiments (video) that pry information from the interloper. Each particle entering the transition radiation detector releases radiation that hints at its mass. Next, the silicon tracker charts the particle’s path based on the electric current it leaves in its wake, while the time-of-flight system measures its velocity. A ring image
Cerenkov counter analyzes the spray of light given off by particles as they crash through a porous material called an aerogel; that light reveals the particles’ speed before their final collision into the energy-measuring electromagnetic calorimeter—a lead brick laced with optical fibers. All the while, two GPS-enabled star trackers keep the AMS oriented correctly and a thermal system keeps all the equipment within its proper operating temperature range of –40 to 90 degrees Fahrenheit.
More than 500 participants from 16 countries are collaborating on the $2 billion AMS. “It’s probing the foundations of the universe,” says NASA project manager Trent D. Martin. “We’ll collect data for 10 years and then study it for 30 or 40.”