Radiation and the International Space Station Recommendations to Reduce Risk (2000) / Chapter Skim
Currently Skimming:
1 Scoping the Problem
1 Scoping the Problem
Pages 7-23
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From page 7... ...
The scene might have been inspired by the great solar storm of August 4, 1972, which like William Tell's apple-splitting arrow, split the 8 months between the last two Apollo Moon landings evenly. It delivered a total dose of radiation over half a day that, had it missed the middle and hit the Apollo mission at either end, would have caused the crew in the lunar module to suffer acute radiation sickness and, given the uncertainty in the estimate, possibly even death.2 The International Space Station (ISS)
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above about 60 degrees. Geomagnetic storms, which are terrestrial responses to solar storms, weaken this shielding and allow solar energetic particles to penetrate to lower altitudes and latitudes.
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This report focuses on solar energetic particles with energies higher than 10 MeV and outer radiation belt electrons with energies higher than 0.5 MeV. These are the energies at which protons and electrons penetrate space suits.
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1.2 SPACE WEATHER CONTEXT This section gives a short overview of the phenomena that make up space weather.7 The term "space weather" refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of spaceborne and ground-based technological systems and that can affect human life or health.8 The Sun ultimately drives all space weather phenomena by means of the solar wind (the hot, magnetized plasma flowing nearly radially outward from the Sun at all times) and solar storms (flares, prominence eruptions, and coronal mass ejections (CMEs)
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From page 11... ...
The more energetic the proton, the farther it can penetrate onto closed field lines. During geomagnetic storms, the solar wind or CME compresses the magnetosphere more severely, more field lines open as a result of magnetic reconnection, and the polar cap grows.
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From page 12... ...
A recent update of this report suggests reducing the recommended career limit, still based on a 3 percent risk of induced cancer, by a factor of two. The new recommended career limits are in line with international limits set for workers in terrestrial radiation environments.
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From page 13... ...
Whereas satellite encounters with the SAA are as predictable as the tides, usually solar energetic particles, geomagnetic storms, and high-speed solar wind streams are not reliably predictable, nor is the intensity of the associated radiation event. The high-inclination orbit of ISS therefore introduces a new radiation risk factor.
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From page 14... ...
One group crosses the SAA on the descending leg of the orbits, a second group crosses it on the ascending leg of the orbits, and a third group crosses the SPE zones. The figure also shows that as the ISS moves along its 16 orbits per day, its per-orbit risk of exposure to solar energetic particles varies from zero to a maximum that depends on the size of the SPE zones.
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based on simplified geometry. The bottom panel shows radiation data from the Mir space station during a non-SPE orbit (line 3)
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The shape of line 1 suggests that the effective radius of the SPE zones at this time was between 30 and 35 degrees, since the dose per orbit drops substantially around 150 and 270 degrees longitude of ascending node. To predict the severity of the SPE radiation risk, one also needs to know the dose rates that would represent a worst-case scenario.
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(Sv/hr) 30o 35o 40o 45o 0.15 0.30 0.50 0.06 0.13 0.21 0.20 0.40 0.66 0.29 0.58 0.96 0.36 0.72 1.20 NOTE: Space suit shielding is assumed to be equivalent to about 0.5 g/cm2 Al.
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From page 18... ...
This unit has multiple responsibilities: provide preflight crew exposure projections; provide real-time astronaut radiation protection support; provide radiation monitoring to meet medical and legal requirements; maintain comprehensive crew exposure modeling capability; provide preflight planning and analysis support; and provide in-flight support. In-flight support entails specific responsibilities, among them the following: provide updated EVA exposure analysis to the flight surgeon; provide EVA start and stop times to the flight surgeon; provide an EVA go/no go recommendation prior to egress; monitor real-time space weather; recommend whether to continue or terminate an EVA during a radiation event; track exposure from the nominal radiation environment; monitor extravehicular charged-particle directional spectrometer data when they become available starting in June of 2000; and provide a
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The Apollo missions were scheduled to take place during solar maximum years, when large solar particle events are more apt to occur. Research had established that virtually all particle events during solar cycle 19 were preceded by type IV solar radio bursts.
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. The high-latitude radiation environments (energetic particles from solar storms and relativistic electrons in Earth's outer radiation belt)
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Chang, and M.Y. Kim, "Shielding from solar particle event exposures in deep space," in Proceedings of Workshop on Impact of Solar Energetic Particle Events for Design of Human Missions, September 9-11, 1997, Center for Advanced Space Studies, Houston.
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Turner and C Kemere, "Solar particle events and International Space Station," Report submitted to the Committee on Solar and Space Physics, August 12, 1998.
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From page 23... ...
before making recommendations to the flight director regarding actions to reduce crew radiation exposure. Such a consultation might occur, for example, as astronauts prepare to leave the relative safety of the ISS for an EVA, or while an EVA is under way.
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