Question

Estimate all radiation risks for astronauts after travel from the Earth to the Mars and back. Duration of the travel is 1.5 years. Total absorbed dose will be around 6Gy. Discuss validity of your estimation for all risks (strong and weak sides of the estimation)

Answer 1

Risk of cancer: The evidence for cancer risks from humans exposed to radiation is extensive for doses above 100 millisieverts (mSv). There are uncertainties for lower doses and in transferring risks between populations with different genetic and dietary attributes. Human epidemiology can be applied to space exposures; however, there are additional uncertainties related to the quality of radiation in space, while the doses to be expected on space missions are well understood.

Risk of Central Nervous System effects: At this time, reliable projections for Central Nervous System (CNS) risks from space radiation exposure cannot be made due to limited data on the effects of high radiation on the nervous system. The existing animal and cellular data show that space-like radiation can produce molecular, structural, functional, and behavioral effects at doses comparable to reference mission projections. If human responses closely resemble those in animal models, the possibility exists for impacts on mission operations and/or late degenerative changes.

Risk of degenerative tissue: The association between ionizing radiation exposure and the long-term development of degenerative tissue effects such as heart disease, cataracts, immunological changes, and premature aging is well-established for moderate to high doses of radiation. The majority of this evidence is derived from epidemiological studies on the A-bomb survivors in Japan, radiotherapy patients, and occupationally exposed workers and is supported by laboratory studies using animal models (Blakely et al. 2010) and studies of cataracts in astronauts (Cucinotta et al. 2001; Chylack et al. 2009, 2012). The risks for these diseases from low dose-rate exposures are much more difficult to assess due to their multifactorial nature and long latency periods where animals must be observed; therefore, these risks remain debatable for ISS or short-term lunar missions but are more likely in long-term lunar or Mars missions. It also remains unclear whether low-dose exposures influence the same biological pathways that have been shown to be involved in disease progression following moderate- to high-dose radiation exposures (Little et al. 2008). Research to address the possible role of chronic inflammation and increased oxidative stress associated with space radiation exposure will need to be conducted. As mission duration increases, there could be degenerative risks to other tissues related to digestive diseases and pulmonary changes that become a concern.

Risk due to acute radiation: The biological effects of space radiation, including Acute Radiation Risks (ARS), are a significant concern for manned spaceflight. The primary data that are currently available are derived from analyses of medical patients and persons accidentally exposed to high doses of radiation. High doses of radiation can induce profound radiation sickness and death. Lower doses of radiation induce symptoms that are much milder physiologically but that pose operational risks that may be equally serious. Both scenarios have the potential to seriously affect crew health and/or prevent the completion of mission objectives.