Space Radiation Hazards and the Vision for Space Exploration Report of a Workshop (2006) / Chapter Skim
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1 Radiation Risks and the Vision for Space Exploration
1 Radiation Risks and the Vision for Space Exploration
Pages 7-23
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From page 7... ...
In the ensuing three decades, various studies of the possible absorbed doses from this August 1972 event and their potential biological effects on human crews have been carried out (e.g., Wilson and Denn, 1976; Townsend et al., 1991, 1992; Wilson et al., 1997; Parsons and Townsend, 2000)
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From page 8... ...
with the Sun's ~11 year activity cycle has been well established on the basis of direct measurements made over the past 70 years,first from the ground and later with ground-based and space-based instruments.It has been known since the early 1960s that GCR fluxes are modulated by the interplanetary magnetic field (IMF) and are anticorrelated with solar activity, with the lowest fluxes occurring when solar activity is highest and vice versa (Figure 1.1.1)
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From page 9... ...
, they cover too short a time period to capture longer-term, secular variations that are also important for an understanding of the space radiation environment and the solar processes that influence it.Fortunately, however, when galactic cosmic radiation and solar energetic particles interact with Earth's atmosphere, they trigger nuclear and chemical reactions, the products of which, deposited and preserved in the polar ice, provide a record of cosmic radiation modulation and SEP activity that extends centuries, even millennia, into the past. One of the key products of this process is the 10Be isotope, which attaches itself to aerosols and, after a residence of several months in the atmosphere, precipitates onto Earth's surface.
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From page 10... ...
.The frequency with which large events occurred during earlier epochs was 6 to 8 times greater than the frequency of SEP events during the period from about 1960 to the present, which appears to be the minimum of the Gleissberg cycle that began circa 1910 (Figure 1.1.3, McCracken et al., 2001b)
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From page 11... ...
Analysis of the 10Be and nitrate data not only makes possible the characterization of the past radiation environment at 1 AU;the picture of secular trends in GCR modulation and SEP occurrence derived from the ice core data also serves as an invaluable source of information about solar activity and heliospheric conditions over timescales of millennia, information not available from any of the other historical data records.
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From page 12... ...
Anomalous cosmic rays, accelerated at the solar wind termination, are judged not to pose a hazard. An additional important source of radiation are the secondary neutrons 2A sievert unit is the amount of ionizing radiation dose equivalent required to produce the same biological effect as 100 rads of high-penetration x-rays.
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From page 13... ...
. Galactic Cosmic Radiation Galactic cosmic rays are highly energetic nuclei (mainly in the range 100 MeV per nucleon to 10 GeV per nucleon)
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From page 14... ...
RADIATION RISkS NASA is required by law to limit radiation exposure to humans in space and to implement appropriate risk mitigation measures in order to ensure that humans can safely live and work in the space radiation environment, anywhere, anytime. In this context, "safely" means that acceptable risks are not exceeded during crew members' lifetimes, where "acceptable risks" include limits on postmission and multimission consequences (e.g., excess lifetime fatal cancer risk)
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From page 15... ...
Although a detailed analysis of specific risks was beyond the scope of the workshop, the radiation protection community has established that at low doses and low dose rates, radiation exposure limits that adequately protect individuals from excessive increases in cancer rates also protect them from acute risks. 7The GCR heavy ions, which contribute most of the dose equivalent, have nuclear collision mean free paths and ranges that are significantly less than those of the high-energy protons.
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From page 16... ...
However, there is some basis for concern that the HZE component of the space radiation environment may produce unique damage leading to degenerative tissue effects and/or central nervous system damage. This question is the subject of ongoing research using simulated galactic cosmic ray irradiation (see Box 1.2, "The NASA Space Radiation Program")
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From page 17... ...
The beams used generally consist of a single particle at a single energy, but mixed beams and multi-energy beams can be delivered, for example, to simulate the solar particle event spectrum of protons or the distribution of galactic cosmic rays. Beam-time proposals are reviewed by a Brookhaven/NASA science advisory committee with physics, biology, and engineering members to ensure compatibility between experiments, proper infrastructure support, and appropriate experiment design.
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From page 18... ...
For HZE radiation, carcinogenesis may be nearly independent of dose rate, while acute risks depend very strongly on dose rate. Consequently, the risk due to acute effects depends strongly on the magnitude of solar particle events, while the risk due to carcinogenesis depends on the total dose equivalent.
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From page 19... ...
Calculations were made near solar minimum where highest galactic cosmic radiation exposures occur. SOURCE: Adapted from Cucinotta et al.
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From page 20... ...
Not only are galactic cosmic rays (specifically the heavy-ion component) important in causing space environment effects on hardware, but protons and heavy ions from solar particle events or in the trapped radiation belts (especially in Earth's South Atlantic Anomaly region)
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From page 21... ...
RADIATION RISKS AND THE VISION FOR SPACE EXPLORATION 21 FIGURE 1.2 Space weather and its effects.(Top) The connected Sun-Earth system.A large coronal mass ejection propagates from the Sun toward Earth and its magnetosphere.
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From page 22... ...
1992. An improved model of galactic cosmic radiation for space exploration missions.
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From page 23... ...
2005. Interplanetary crew dose estimates for worst case solar particle events based on the historical data for the Carrington flare of 1859.
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