Research that started aboard balloons a century ago soon culminated into a three-year stint aboard the International Space Station as scientists work on solving a fundamental astrophysics mystery: what gives cosmic rays such incredible energies, and how does that affect the composition of the universe?
Cosmic Ray Energetics and Mass (CREAM) is an experiment to determine the composition of cosmic rays up to the 1015 eV (also known as the “knee prospect”) in the cosmic ray spectrum.
It has been hypothesized that the knee prospect of the cosmic ray spectrum can be explained by the theoretical maximum energy that a supernova can accelerate particles to according to Fermi acceleration.
The measurements are accomplished using a timing-based charge detector and transition radiation detector sent to an altitude of at least 110,000 ft with aid of a high-altitude balloon.
After launching from McMurdo Station in Antarctica, the balloon will stay aloft for 60–100 days gathering data on charges and energies of the unimpeded cosmic rays that strike the detectors.
Can the “knee” be explained by maximum acceleration due to supernovae?
Have the composition of cosmic rays changed over time?
Are multiple mechanisms responsible for the production of cosmic rays?
Cosmic Ray Energetics and Mass (CREAM) will be the first cosmic ray instrument designed to detect at such higher energy ranges, and over such an extended duration in space.
Scientists hope to discover whether cosmic rays are accelerated by a single cause, which is believed to be supernovae. The new research also could determine why there are fewer cosmic rays detected at very high energies than are theorized to exist.
Cosmic rays are energetic particles from outer space. They provide a direct sample of matter from outside the solar system. Measurements have shown that these particles can have energies as high as 100,000 trillion electron volts. This is an enormous energy, far beyond and above any energy that can be generated with manmade accelerators, even the Large Hadron Collider at CERN.
Researchers also plan to study the decline in cosmic ray detection, called the spectral “knee” that occurs at about a thousand trillion electron-volts (eV), which is about 2 billion times more powerful than the emissions in a medical nuclear imaging scan. Whatever causes cosmic rays, or filters them as they move through the galaxy, takes a bite out of the population from 1,000 trillion electron-volts upwards. Further, the spectrum for cosmic rays extends much farther beyond what supernovas are believed to be able to produce.
To tackle these questions, NASA plans to place CREAM aboard the space station, becoming ISS-CREAM. The instrument has flown six times for a total of 161 days on long-duration balloons circling the South Pole, where Earth’s magnetic field lines are essentially vertical.
ISS-CREAM is being developed as an international collaboration, including teams from the United States, Republic of Korea, Mexico and France, led by Professor Eun-Suk Seo of the University of Maryland in College Park, Md.
Even though CREAM balloon flights reached high altitudes, enough atmosphere remained above to interfere with measurements. The plan to mount the instrument to the exterior of the space station will place it above the obscuring effects of the atmosphere, at an altitude of 250 miles (400 kilometers).