Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations

In addition to traditional interest by various governments in space exploration, there is growing interest in private missions to Mars and other deep space destinations within the next decade. Private missions could consider persons not restricted by radiation limits; however there remains an interest in the level of risk to be encountered. The major risk for space travel is cancer from galactic cosmic rays (GCR), while circulatory diseases in suggested in some but not all epidemiology studies at modest doses (< 1 Gy) and detriments in cognition are suggested by rodent studies following acute irradiation with moderate doses of heavy ions. The GCR are not easily shielded since they consist of high energy protons, heavy ions and secondary radiation produced in shielding and tissue. Furthermore heavy ions are more effective per unit dose in causing solid cancers compared to gamma-rays. In addition non-targeted effects (NTEs) are suggested by most low dose radiobiology studies to increase biological effectiveness for low doses of high LET radiation. Astronauts and cosmonauts are typically above 40-y, while younger aged persons could participate in private space missions. In this paper, we describe cancer and circulatory disease risks for a 940 d Mars mission for average solar minimum conditions for persons of varying ages from 20 to 60 years. For the first-time NTEs are considered in Mars mission cancer risk predictions. Cancer morbidity risks and 95% confidence intervals for age 20-y persons are predicted as 20.9% [7.04, 51.4] and 12.7% [4.97, 29.3] for females and males, respectively. We find that cancer fatality risks decline with age of exposure while circulatory disease risks are nearly independent of age of exposure. The ratio of cancer to circulatory disease fatalities decreases from about 8-to-1 at 20 y to 5-to-1 at 60 y in females and 4-to-1 and 2.5-to-1 in males with about 2-times higher loss of life expectancy for cancer deaths compared to circulatory related deaths, indicating the much higher importance of cancer risk compared to circulatory disease risks for persons participating in space missions.