LOCAL TISSUE DOSES IN A MISSION BEYOND EARTH’S MAGNETOSPHERE BEHIND VARIOUS SPACECRAFT SHIELDING WITH CONSIDERATION OF THE DECREASES OF PROTONS AND HELIUM IONS EFFECTIVENESS

The paper presents the contemporary view of the risks from space radiation, retrospective of dose limits regulation, total risk estimation and plausible lifespan reduction in consequence of extended orbital and exploration missions. The authors analyze the potential of thickening the aluminum-polyethylene shielding to reduce doses from galactic space radiation (GSR) in space exploration missions. For this purpose, dose calculation was performed with consideration of the times reduction of the effectiveness of protons and GSR helium ions with low dose rate owing to a rapid reparation of cells in radiation-sensitive tissues. It was shown that dependence the new quality factor (QF) on linear energy transfer (LET) to tissues and reduction of the protons and helium ions effectiveness in comparison to the existing calculational techniques reduces 2-3 folds the annual local tissue equivalent doses behind a 30–100 g/cm2 aluminum shield and 3-4 folds behind polyethylene. With the new QF -LET dependence, the multiple dose reduction due to buildingup of the shielding thickness compensates the double dose growth behind thin shielding.