Abstract
The project ALTEA-shield/survey is part of an European Space Agency (ESA) – ILSRA (International Life Science Research Announcement) program and provides a detailed study of the International Space Station (ISS) (USLab and partly Columbus) radiation environment. The experiment spans over 2 years, from September 20, 2010 to September 30, 2012, for a total of about 1.5 years of effective measurements. The ALTEA detector system measures all heavy ions above helium and, to a limited extent, hydrogen and helium (respectively, in 25 Mev–45 MeV and 25 MeV/n–250 MeV/n energy windows) while tracking every individual particle. It measures independently the radiation along the three ISS coordinate axes. The data presented consist of flux, dose, and dose equivalent over the time of investigation, at the different surveyed locations. Data are selected from the different geographic regions (low and high latitudes and South Atlantic Anomaly, SAA). Even with a limited acceptance window for the proton contribution, the flux/dose/dose equivalent results as well as the radiation spectra provide information on how the radiation risks change in the different surveyed sites. The large changes in radiation environment found among the measured sites, due to the different shield/mass distribution, require a detailed Computer-Aided Design (CAD) model to be used together with these measurements for the validation of radiation models in space habitats. Altitude also affects measured radiation, especially in the SAA. In the period of measurements, the altitude (averaged over each minute) ranged from 339 km to 447 km. Measurements show the significant shielding effect of the ISS truss, responsible for a consistent amount of reduction in dose equivalent (and so in radiation quality). Measured Galactic Cosmic Ray (GCR) dose rates at high latitude range from 0.354 ± 0.002 nGy/s to 0.770 ± 0.006 nGy/s while dose equivalent from 1.21 ± 0.04 nSv/s to 6.05 ± 0.09 nSv/s. The radiation variation over the SAA is studied. Even with the reduced proton sensitivity, the high day-by-day variability, as well as the strong altitude dependence is clearly observed. The ability of filtering out this contribution from the data is presented as a tool to construct a radiation data set well mimicking deep space radiation, useful for model validations and improvements.
Highlights
Radiation is an important issue in human space exploration (Durante & Cucinotta 2011)
During human deep space exploration, the astronauts will be exposed to the Galactic Cosmic Rays (GCRs) and to the radiation associated with transient solar events (SPEs, Solar Particle Events)
Dose rates and dose equivalent rates as well as spectra will be presented for high latitude (Figs. 6–11), with two exceptions: a spectrum relative to low latitude, to show the filtering effects of the magnetosphere, and dose data relative only to the South Atlantic Anomaly (SAA) (Fig. 13) to document the variability of this component
Summary
Radiation is an important issue in human space exploration (Durante & Cucinotta 2011). At the International Space Station (ISS) altitude (about 400 km) the atmosphere is extremely rarefied and the deflective power of the magnetic field during high latitude passes is limited. Radiation damage to living cells/tissues/organs is demonstrated in the literature for the high doses/dose rates typical of nuclear bombing (Hiroshima and Nagasaki) or, in a more limited extent, to accidents in nuclear power plants, and in the case of long exposures at much lower radiation rates such as those experienced in space from GCR. For a correct risk assessment the impinging radiation should be known with more details: the rate, the distribution in space, the energy released by each ion, or, better, the charge of the ion (Z value) and its kinetic energy Ek (Cucinotta et al 2013)
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