Radiation Protection Today Winter 2021 - Page 9

Manned Space Travel : Addressing The Radiation Issues

Rick Tanner is Group Leader for Radiation Metrology at the UK Health Security Agency . He has a long-standing interest in the radiation protection of flight crews and astronauts , and is a member of the UK Government ' s Space Weather Steering Group and Space Environment Impacts Steering Group . In this article , he describes the human radiation protection issues associated with space tourism and planned missions to the Moon and Mars .
Whilst radiation doses to astronauts are not the media ' s main interest in space , conferences on radiation in space love to have real astronauts as star speakers . Their presentations tend to be mainly about how much fun it is to be in space , but sometimes you get interesting insights for radiation protection . In one , an astronaut asked the audience what we think astronauts see when they close their eyes ? The answer from the astronaut himself : “ blue flashes ”. These are Cherenkov radiation emitted when a particle passing through the eye is exceeding the speed of light in aqueous or vitreous humour . These particles are clearly penetrating , energetic and depositing a lot of energy .
A second insight came when I was speaking at a conference just before the , now sadly late , Piers Sellars , one of the first UK astronauts . Following my presentation on the radiation doses , he commented that he would take on the Mars trip even if it were only one way ; the radiation doses did not concern him at all . This is clearly not an attitude that we can accept in conventional workplaces . But it is understandable , given the other risks involved .
Radiation Protection Today Winter 2021
Spacecraft are exposed to three distinct sources of ionising radiation : protons , electrons and helium ions from the Sun ; charged particles generated outside the Solar System , known as galactic cosmic rays ( GCR ); protons trapped in the Earth ' s magnetic field . Each of these sources includes particles with very high energies relative to most terrestrial
21 workplaces , up to 10 eV in the case of GCR . These particles also deposit energy via more intense local ionisation than photons and electrons can . Further , the spacecraft itself forms an additional source of radiation , generating other types of radiation , especially neutrons , which contribute significantly to the astronauts ' exposure .
Unlike conventional workers , astronauts can ' t “ go home ” at the end of their working day , so their exposures are to both relatively high dose rates and long durations , resulting in high doses . Their radiation exposures would not be tolerated in any other planned or existing exposure scenario , but if standard radiation protection practice were followed , human exploration of space would not be possible . It must also be remembered that conventional radiation protection assumes a 40 year career , whereas astronauts might get only one mission , though a Mars return trip will be a long one .
The GCR field is effectively constant in deep space , but within the Solar System the cosmic radiation dose rates vary , with the 11-year solar cycle being the main influence . At solar maximum the stronger solar wind reduces the impact of the GCR component , and dose rates are actually lower on average . However , solar maximum brings explosive events on the surface of the Sun , which can create storms of high-energy solar protons : these can lead to very significantly enhanced dose rates . Whilst we know of major recent events , with 1859 ( the Carrington Event ), 1956 and 1989 standing out , tree ring records show