Space Radiation Cancer Risks and Uncertainties for Mars Missions

TLDR

Cancer risk projections from space radiation are highly uncertain due to limited human data, scarce radiobiology for high‑energy HZE ions, and varying uncertainties across biological and physical factors. The study assesses uncertainty in space‑radiation cancer risk projections by applying Monte Carlo sampling of subjective error distributions within a linear‑additivity model. The authors perform Monte Carlo calculations using space‑radiation environment and transport codes for multiple Mars mission scenarios within the linear‑additivity framework. The analysis yields 400–600 % uncertainty in Mars‑mission cancer risk estimates, dominated by quality‑factor uncertainty, rendering long‑term missions outside Earth’s magnetosphere unacceptable under current safety standards, and indicating that low‑dose‑rate dose‑response shape adds further uncertainty.

Abstract

Projecting cancer risks from exposure to space radiation is highly uncertain because of the absence of data for humans and because of the limited radiobiology data available for estimating late effects from the high-energy and charge (HZE) ions present in the galactic cosmic rays (GCR). Cancer risk projections involve many biological and physical factors, each of which has a differential range of uncertainty due to the lack of data and knowledge. We discuss an uncertainty assessment within the linear-additivity model using the approach of Monte Carlo sampling from subjective error distributions that represent the lack of knowledge in each factor to quantify the overall uncertainty in risk projections. Calculations are performed using the space radiation environment and transport codes for several Mars mission scenarios. This approach leads to estimates of the uncertainties in cancer risk projections of 400-600% for a Mars mission. The uncertainties in the quality factors are dominant. Using safety standards developed for low-Earth orbit, long-term space missions (>90 days) outside the Earth's magnetic field are currently unacceptable if the confidence levels in risk projections are considered. Because GCR exposures involve multiple particle or delta-ray tracks per cellular array, our results suggest that the shape of the dose response at low dose rates may be an additional uncertainty for estimating space radiation risks.