Some involved individuals claim that the risk of radiation, which will take the astronauts into the lower of the two Van Allen radiation belts, is exaggerated. Maybe, maybe not. The published papers are somewhat contradictory.
Look at (Nature) Apollo Lunar Astronauts Show Higher Cardiovascular Disease Mortality: Possible Deep Space Radiation Effects on the Vascular Endothelium. Forget about the Van Allen belts. Forget what you think you know about space radiation or cosmic rays, which are compared in popular media to so many chest X-rays or CAT scans.
You thought this was going to be about cancer. Well, it ain’t. The paper observes that those Apollo astronauts who actually went all the way to lunar orbit had 5X the rate of cardiovascular disease of those astronauts who never ventured beyond low earth orbit. The paper identifies a probable cause, which is not passage through the Van Allen belts.
Probable cause: Earth has a controlling effect on the magnetic environment up to an altitude of about 50,000 miles. Above that, on their way to the Moon, they were exposed to elevated HZE radiation, mostly ions of iron (Fe+) traveling near the speed of light. They are pico-scale rifle bullets, damaging a path of tissue several hundred nanometers wide. Quoting from HZE Radiation Non-Targeted Effects on the Microenvironment That Mediate Mammary Carcinogenesis,
The galactic cosmic radiation environment consists of high atomic number (Z) and energy (HZE) charged particles that are characterized by high linear energy transfer (LET) along the particle track, i.e., densely ionizing, … During a 3-year flight in extra-magnetospheric space, 3% of the cells of the human body would be traversed on average by one Fe ion (3).
According to Apollo Lunar Astronauts Show Higher Cardiovascular Disease Mortality, the above is a likely explanation for elevated CVD:
However, when considered as a separate group, the Apollo lunar astronauts, the only group of humans to have traveled outside of the Earth’s protective magnetosphere, demonstrate a higher mortality rate due to CVD compared to both the cohort of astronauts that did not travel into space, as well as astronauts who remained in LEO (Fig. 1). …
although other explanations cannot be completely excluded. Now look at (NIH) The Effects of Galactic Cosmic Rays on the Central Nervous System: From Negative to Unexpectedly Positive Effects That Astronauts May Encounter; focus on Figure 1 and associated discussion. Quoting,
Indeed, despite the lower dose of HZE onboard ISS, the composition (Figure 1) and the chronic nature of the exposure makes orbital flight an actual model of radiation load on the Mars surface. Moreover, on the surface of Mars, astronauts will be additionally protected by the hull of the living module, which will lead to some reduction in the equivalent dose.
There is a contradiction. The discussion of Figure 1 asserts that the ISS astronauts are in a fairly high HZE environment. Over 25 years of the ISS, excess CVD mortality has not been reported. Yet the moon-voyagers, whose exposure was brief, did have excess.
The two papers are not in exact opposition, though contradiction results. Which is more credible? The Effects of Galactic Cosmic Rays on the Central Nervous System relies on complex formulas to calculate the combined effects of disparate forms of radiation. The formulas have never been validated for the purpose. The conclusion, which emphasizes travel to Mars, is unjustifiably rosy.
Apollo Lunar Astronauts Show Higher Cardiovascular Disease Mortality has two parts. The first is purely observational; the second a lab study. The observational part is simple: They went to the Moon, and they were damaged. We will not speak of Mars.
And you won’t sell me a ticket to the inner Van Allen belt, a celestial CAT scanner. With decades of research, HZE or no, the hazard of the Van Allen belts cannot be ignored. The belts damage even radiation hardened satellites.
There are alternatives. We are on the cusp of creation of androids, designed for the harsh environment of space, capable of conveying the emotional experience of human astronauts, yet caring not whether they live or die. The Greeks, and Virgil, did it even cheaper, with epic poetry.
Or, we could just stay home. Is there a Stockton Rush complex?