The Naval Research Laboratory's
(NRL's) Trapped Ions in Space (TRIS) flew as a Get Away Special
payload onboard NASA space shuttle mission STS-76, the recent
nine-day mission that ended on March 31. TRIS measured a
recently-discovered
belt of energetic cosmic ray nuclei trapped in Earth's magnetic
field to quantify radiation hazards in space and lead to a better
theoretical understanding of how these cosmic ray nuclei have
become trapped in the Earth's magnetic field. Analysis of TRIS
data will begin sometime after the detectors are returned to
the Laboratory later this month.
So-called "anomalous cosmic
rays," which originate in the nearby interstellar medium,
form the radiation belt which TRIS will observe. These trapped
anomalous cosmic rays, say the researchers, have sufficient energy
to pose a potential radiation hazard to some lightly shielded
electronic systems planned for the International Space Station
(ISS) and perhaps to astronauts during extravehicular activity
in certain parts of the orbit.
Although the existence of this
radiation belt was predicted by scientists in 1977, it was not
discovered until 1991, when an NRL-led team of U.S. and Russian
scientists compared satellite data from both countries. Since
1992, trapped anomalous cosmic rays have also been observed by
experiments aboard NASA's Solar, Anomalous, and Magnetospheric
Particle Experiment (SAMPEX) satellite at an altitude of about
600 kilometers (km), or 375 miles. At present, however, there
is insufficient theoretical understanding of trapped anomalous
cosmic rays to extrapolate from the SAMPEX observations down
to altitudes of roughly 350-450 km (approximately 220-280 miles),
where the Russian MIR Space Station is located and where the
ISS will operate. Scientists will be able to compare simultaneous
observations from TRIS and SAMPEX to bridge this gap.
TRIS, which previously flew on
a NASA mission in 1984, measures and identifies cosmic ray nuclei
using polycarbonate detectors, including some of the same type
that is routinely used in the astronauts' dosimeter badges. Ionizing
particles produce trails of radiation damage as they pass through
these detectors. After return from space, the detectors are chemically
etched in the laboratory to reveal the damage trails, which are
then measured with high-precision microscopes. The atomic number,
energy, and arrival direction of the cosmic ray nuclei are determined
from these measurements.
TRIS was built by NRL's Space
Science Division under the leadership of Dr. James. H. Adams,
of the Cosmic Ray Physics Section, the principal investigator
for the TRIS experiment. The flight is being sponsored by the
U.S. Air Force Space Test Program office at the Johnson Space
Center.
The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of nearly 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 85 years and continues to meet the complex technological challenges of today's world. For more information, visit the NRL homepage or join the conversation on Twitter, Facebook, and YouTube.
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