Space radiation has long been recognized as a risk for the human exploration of deep space. Dose rates in space are, with the exception of large, brief Solar Particle Events, not large enough to cause acute illness, but are... [ view full abstract ]
Space radiation has long been recognized as a risk for the human exploration of deep space. Dose rates in space are, with the exception of large, brief Solar Particle Events, not large enough to cause acute illness, but are roughly three orders of magnitude higher than those experienced on Earth. Although space radiation has been the subject of biological studies for decades, the possible health effects of exposure to space radiation remain poorly understood. The exposures are protracted, mostly low-dose with possible brief high-dose periods, and are unlike any received on Earth. While reduction of biological uncertainties remains a top priority, detailed measurements of diverse radiation environments are also important, and have been successfully undertaken in recent years.
Energetic particle detectors that measure radiation environments relevant to human exploration are currently deployed in lunar orbit (the Cosmic Ray Telescope for the Effects of Radiation, or CRaTER, aboard the LRO spacecraft), Mars (the Mars Science Laboratory's Radiation Assessment Detector aboard the Curiosity rover), and on the International Space Station (ISS-RAD). The instruments are all capable of fully characterizing the various charged-particle environments, with varying degrees of capability for measuring neutrons. When solar activity is relatively low, as it has been for the past several years, charged-particle environments are dominated by Galactic Cosmic Rays (GCRs) and the secondary products they create when they interact with shielding materials such as the Martian atmosphere or the hull of the ISS. Interactions in shielding may also create secondary neutrons, which increase in importance as shielding depth increases. In addition to bulk shielding, geomagnetic shielding also plays a significant role for spacecraft in low-Earth orbit (LEO). The LEO environment is further complicated by the existence of the South Atlantic Anomaly (SAA), a region containing magnetically trapped protons and electrons through which the ISS passes several times per day.
The three instruments mentioned above provide data from four distinct environments: free space (CRaTER); free space under modest shielding comprised of 6 to 9 g cm-2 of tissue-equivalent plastic (CRaTER); a planetary surface under about 22 g cm-2 of CO2 (MSL-RAD); and LEO, with rapidly-varying magnetic shielding and several tens of g cm-2 of bulk shielding. Because most GCRs are highly energetic, they are able to penetrate considerable shielding depths, and for the depths at which these instruments are located, the measurements yield broadly similar results in terms of total flux and dose rate. However, heavy ions -- which contribute significantly to the uncertainties in biological response to space radiation -- are readily attenuated by shielding, and these vary significantly in the different environments, as do the neutron fluxes. Results from CRaTER and both RAD instruments will be presented and compared to each other. Comparisons to model calculations will also be presented.
Observations , Radiation Effects (e.g., SEE, TID, DDD) , Radiation