Characterization of the Radiation Shielding Properties of US andRussian EVA Suits Page: 3 of 34
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Eril Research, Inc.
station. In order to assess the radiation shielding effectiveness of the US and Russian
EVA suits, both of which will be used during ISS assembly, one suit of each type was
brought to the Loma Linda University Medical Center (LLUMC) and exposed to beams
of monoenergetic protons at two energies and to a beam of monoenergetic electrons at
one energy. At the behest of the NASA Johnson Space Center's Space Radiation Health
Project, Eril Research, Inc. (ERI) participated with a number of other investigators in
characterizing the radiation shielding properties of the two EVA suits.
In the 51.560 inclination, ~400 km altitude orbit of the ISS, it is trapped protons and
electrons which are of principle concern to astronaut health and safety during EVA.
Trapped electrons range in energy up to ~6 MeV and are encountered while the station is
at high latitudes and passing through the cusps of the trapped electron belt [2]. The
spectrum of trapped protons extends from several MeV up to several hundred MeV, with
a broad peak between ~150 and ~250 MeV. The trapped proton flux is greatest when the
ISS is passing through the South Atlantic Anomaly (SAA), a region off the coast of
Brazil where the Earth's magnetic field dips unusually low, allowing trapped protons to
intersect the orbit of the ISS [2]. All but the most energetic electrons and a substantial
fraction of the trapped proton flux are attenuated within the shielding represented by the
outer structure of the ISS. However, during EVA astronauts are protected only by the
shielding provided by their suits, which is substantially less than that provided by the
structure of the ISS. This decreased shielding permits lower energy particles to penetrate
the body of the astronaut, increasing his total radiation exposure. Doses measured in the
Russian Orlan suit during a 1997 EVA on the Russian Mir Orbital Station using the
Hungarian Pille portable TLD system were three to four and half times greater than that
measured inside the Mir during the same time period [3].
Two types of EVA suit were tested. The Extravehicular Mobility Suit (EMU),
manufactured for NASA by ILC Dover, is the current design of US EVA suit used aboard
the Space Shuttle and the ISS. The Orlan (Eagle) -M suit, produced by NPP Zvezda, is
the current Russian EVA suit and has been previously used aboard the Mir Orbital
Station. An example of each suit was used in radiation exposures at LLUMC. In addition,
swatches of suit material from each type of suit were used in some of the exposures. A
tissue equivalent human phantom was used to simulate an astronaut body. Detectors were
exposed at specific organ sites of interest in the phantom while wearing the suits.
Radiation detectors were exposed behind portions of the suit to monoenergetic electrons
of 6 MeV and to monoenergetic protons of two energies: 60 MeV and 232 MeV. The
choice of electron and proton energies was dictated both by the radiation environment
present outside the station in the ISS orbit and by the capabilities of the radiation
facilities at LLUMC.
The objective of the ERI measurements made during both the 6 MeV electron and 60
MeV proton irradiations was to measure dose as a function of depth behind each of the
two EVA suits and inside the two EVA helmets. For these measurements, stacks of
thermoluminescent detectors (TLDs) were exposed perpendicular to the electron and
proton beams behind swatches of EVA suit material and behind the visors of the EVA
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Benton, E. R.; Benton, E. V. & Frank, A. L. Characterization of the Radiation Shielding Properties of US andRussian EVA Suits, report, October 26, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc890113/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.