Abstract
In lunar and Mars missions, astronauts fly outside the Earth magnetosphere and will be exposed usually to galactic cosmic rays (GCR) that are composed of high-energy protons and heavy ions (He-Fe). The effective dose rate is estimated to be about 1 mSv per day. Under this normal condition, their doses would not exceed 1Sv even for an interplanetary mission longer than two years. However, a greatest-scale solar particle event (SPE) would possibly bring a high-dose proton exposure for a short period (several hours to a cup of days), comparable to the total GCR dose. It is thus important to quantify the potential risks of SPE for lunar or Mars missions and to employ necessary countermeasures for reducing the risks. For establishing most effective countermeasures with the least increase of cost, we primarily need to construct a risk-evaluation method applicable to multiple exposures to GCR and SPE that are greatly different in regards to dose rate and its fluctuation. This task requires quantifying synergistic effects of peculiar conditions in space environment such as microgravity, in regard to carcinogenesis and other biological effects (cataracts, heart diseases, damage to central nervous system, etc.) that would be promoted by space radiation exposure.
