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About the Authors:
Francis A. Cucinotta
* E-mail: [email protected]
Affiliations NASA, Lyndon B. Johnson Space Center, Space Radiation Program, Houston, Texas, United States of America, University of Nevada Las Vegas, Department of Health Physics and Diagnostic Sciences, Las Vegas, Nevada, United States of America
Myung-Hee Y. Kim
Affiliation: Universities Space Research Association, Division of Space Life Sciences, Houston, Texas, United States of America
Lori J. Chappell
Affiliation: Universities Space Research Association, Division of Space Life Sciences, Houston, Texas, United States of America
Janice L. Huff
Affiliation: Universities Space Research Association, Division of Space Life Sciences, Houston, Texas, United States of America
Introduction
In space astronauts are exposed to galactic cosmic rays (GCR) comprised of high-energy protons and high charge (Z) and energy (E) (HZE) nuclei and solar particle events (SPE) comprised largely of low to medium energy protons. As space missions venture away from Earth into deep space, long-term exposures occur leading to important concerns about the risks to astronauts, including discussions on the acceptable risk level. A key component of this concern are the types of radiation that occur in space [1]–[6], which produce distinct types of biological damage from radiation on Earth such as X-rays or gamma-rays. Individual radiation sensitivity and estimating risks at low dose-rates are additional major concerns, while potential interactions between space radiation and microgravity found to be a minor concern [1]. Fatal cancer risk [1]–[6] has been considered the dominant risk for GCR and NASA has developed the NASA Space Cancer Risk (NSCR) model to estimate cancer risks and uncertainties for space missions [5], [6]. NASA's radiation standard limits astronaut exposures to a 3% risk of exposure induced death (REID) evaluated at the upper 95% confidence interval (CI) of the risk estimate [7]. However recent epidemiological analysis of radiation risks for circulatory diseases [8]–[10] shows additional risks, and allow for predictions of REID for circulatory diseases to be included with cancer risk predictions [5], [11], [12]. Risks to the central nervous system (CNS) are also a concern [1], [4], however methods to make quantitative risk estimates of CNS effects have not been developed.
Conjunction class Mars missions [13], [14], where Earth and Mars are in favorable alignments, involve long stays on the martian surface of approximately 540-d with transit...