TRACER - the Transition Radiation Array for Cosmic Radiation - will rise to an altitude of 40 kilometers (125,000 feet), practically outside Earth's atmosphere, which facilitates observations of radiation from space. TRACER is an instrument for direct, balloon-borne measurements of cosmic ray nuclei (boron to iron) at very high energies of up to several 1,014 electron volts per nucleus.

For each cosmic ray the nuclear charge, the energy, and the trajectory through the instrument will be measured with detectors including 1,600 gas-filled tubes. Each tube is 2 meters long with a diameter of 2 centimeters, making TRACER the largest cosmic ray detector in the world for observations above the atmosphere.

It measures 2.5 meters by 2.5 meters by 2.5 meters and weighs nearly 2 tons. The entire instrument was produced at the University of Chicago by an international team that is also conducting the scientific mission.

"The cosmic-ray nuclei are a sample of matter arriving here with the speed of light from distant regions of our galaxy," said Dietrich Muller, principal investigator. "Their energies can be enormous, and may far exceed any energy that can be reached in terrestrial laboratories."

Muller said scientists need to "understand the origin of this matter, how nature is able to accelerate the nuclei, which are most likely the remainders of gigantic stellar explosions called supernova remnants, and how they move through the galaxy and interact with the interstellar gas."

He said this process " requires detailed measurements of the energy distributions and relative abundances of the individual elemental components. The measurements must be performed above the earth's atmosphere, and be capable of covering a wide range of energies. Precisely such measurements are conducted with the balloon flight of TRACER."

Related Links
Transition Radiation Array for Cosmic Radiation at SSC