NRL TRIS Experiment to Fly Aboard STS-76

2/29/1996 - 23-96r
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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.

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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 2,800 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 90 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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