INTRODUCTION

Space radiation health risks are a major consideration in planning and carrying out long-term space missions, especially those outside of the Earth's magnetosphere. In support of human missions to Mars, the National Aeronautics and Space Administration (NASA) is currently supporting a substantial research effort to understand the mechanisms underlying the highly efficient induction of biological effects from the high-energy and charge (HZE) component of the galactic cosmic rays. The risks of late effects, most notably cancer, are of the greatest concern; however, single-particle effects are also suspected of posing a risk of cataracts and damage to the central nervous system (1 ,2). Based on recent results from the life-span studies of Japanese A-bomb survivors (3), other risks are also of concern for the higher doses expected on Mars exploration missions. These include risks of acute and chronic non-cancer mortality...