As a member of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), Iran has a long-term space exploration program. Space radiation is one of the challenges facing humans when they go outside Earth's protective atmosphere and magnetic field. Space is an environment that the cardinal principles of radiation protection i.e. time, distance and shielding cannot be effectively applied. On the other hand, well-known limitations of physical shielding prompt us to explore biological methods for inducing radioresistance during space missions. Screening of the candidates of long-term space missions by ground-based in vitro adaptive response studies might be helpful. It has recently been shown that the detrimental effects of exposure to protons and HZE particles can be prevented by some dietary supplements. Interestingly, in contrast with radioprotectors, these dietary supplements can prevent radiation induced detrimental effects even when applied several days after exposure to radiation. It seems that finding appropriate radiation mitigators with a post-exposure time window in excess of 24 hours will be a critical goal in planning future manned space missions. In this paper, the advantages of biological shielding over current well defined physical shielding will be discussed.

Background: Astronauts will be exposed to both chronic space radiation and acute high doses of energetic radiation of solar particle events in long-term deep space missions. The application of radioprotectors in space missions has basic limitations such as their very short time window as well as their acute toxicity and considerable side effects. The aim of the present study was to investigate the potential radiation mitigation effect of vitamin C that is known as an effective antioxidant and free radical scavenger. Materials and Methods: One hundred twenty male Wistar albino rats weighing 250-300 g were randomized into the following study groups: I, control II, Only exposure to gamma-radiation (LD50/30) treated with a single dose of vitamin C, III, 1h before irradiation, IV, V and VI, 1h, 12h and 24 h after irradiation. Measurement of cell viability and proliferation was also performed by using MTT cell proliferation assay. Results: The survival rate in animals received vitamin C 1h, 12h and 24h after irradiation were 55%, 60%, and 80%, respectively. The viability of cells in animals received vitamin C 1h, 12h and 24h after irradiation were 94.9%, 99.0%, and 100%, respectively. The viability of the cells in animals only exposed to gamma rays was 50.1%. Conclusion: These findings reveal that a single dose of vitamin C can potentially be used up to 24 hours after exposure to reduce the detrimental effects of high levels of ionizing radiation in cases such as the occurrence of currently unpredictable solar particle events.

Astronauts are exposed to a wide variety of stressors ranging from radiation and microgravity to persistent fluids shifts, circadian shifts and the psychological stress of prolonged isolation and confinement. On deep space missions, beyond the range of the Earth's magnetosphere, ionizing radiation may increase oxidative stress and DNA damage, immune system dysregulation and alter the effectiveness of the cellular defense mechanisms. By reviewing the health problems reported by astronauts participated in previous space missions, it is evident that viral infections are not rare in space. Recent reports suggest that COVID-19 can last for a long time in communities. Although NASA implements countermeasures designed to limit crew illness during space missions such as a pre-flight quarantine, it is not clear whether an outbreak can be prevented. Currently, it is not likely that astronauts could get a viral infection, but the consequences of potential life-threatening viral diseases such as COVID-19 should be better characterized. In this paper we discuss why COVID-19 fatality in space might be significantly higher than on the Earth. The reasons for such an increased risk include 1) uselessness of social distancing due to microgravity 2) immune system dysregulation 3) possibly higher mutation rates of RNA viruses such as the novel coronavirus (SARS-CoV-2) 4) existence of strong selective pressure and 5) decreased maximum oxygen uptake. Given these considerations, the combined effects of microgravity, space radiation (and possibly other major space stressors) on the immune system of astronauts exposed to SARS-CoV-2 and possible interactions of the virus, space stressors and host should be carefully investigated.