Space Radiation Dosimetry at the Exposure Facility of the International Space Station for the Tanpopo Mission

Abstract

Radiation dosimetry was carried out at the exposure facility (EF) and the pressurized module (PM) of the Japanese Kibo module installed in the International Space Station as one study on environmental monitoring for the Tanpopo mission. Three exposure panels and three references including biological and organic samples and luminescence dosimeters were launched to obtain data for different exposure durations during 3 years from May 2015 to July 2018. The dosimeters were equipped with additional shielding materials (0.55, 2.95, and 6.23 g/cm 2 mass thickness). The relative dose variation, as a function of shielding mass thickness, was observed and compared with Monte Carlo simulations with respect to galactic cosmic rays (GCRs) and typical solar energetic particles (SEPs). The mean annual dose rates were D EF = 231 -5 mGy/year at the EF and D PM = 82 -1 mGy/ year at the PM during the 3 years. The PM is well shielded, and the GCR simulation indicated that the measured mean dose reduction ratio inside the module (D PM /D EF = 0.35) required *26 g/cm 2 additional shielding mass thickness. Observed points of the dose reduction tendency could be explained by the energy ranges of protons (10-100 MeV), where the protons passed through, or were absorbed in, the shielding materials of different mass thickness that surrounded dosimeters.

Four-Year Operation of Tanpopo: Astrobiology Exposure and Micrometeoroid Capture Experiments on the JEM Exposed Facility of the International Space Station

“…The higher shielding inside is reflected in the dose values: the values in space are approximately three times higher than in the ISS pressurized area. The slightly higher dose (0.71 mGy/day) was recorded during the first period from May 2015 to June 2016, compared with the average for the 3 years (0.63 mGy/day), which may be related to the highly intense solar event of >10 MeV protons that occurred in the period from May 2015 to June 2016 as well as the location of a particular EU (Kodaira et al, 2021). The detailed results are reported in this issue (Kodaira et al, 2021).…”

Considerations for practical dose equivalent assessment of space radiation and exposure risk reduction in deep space

“…Error bars represent the statistical error of the calculation. Several space modules provide shielding of ~ 20 g/cm 2 or more mass thickness on average 42 , 43 , therefore, we employed 20 g/cm 2 as the typical thickness of spacecraft shielding. The proton flux was increased by shielding because the target and heavier projectile fragmentation reactions produced numerous secondary protons along the pathway of the primary particles in the materials.…”

“…Here, the dose rate in space is of the order of hundreds of micro grays per day e.g., Refs. 6 , 33 , 34 , 37 , 43 , 57 . Non-targeted effects are expected to be negligible at sufficiently low doses of < 1 mGy e.g., Refs.…”

Microbial adaptation to spaceflight is correlated with bacteriophage-encoded functions

“…UV radiation induced activation of lytic phage is well known ; however, the ISS structure shields the interior from UV radiation. The presence of DNA-repair genes may play a role in the protection of the host genome from galactic cosmic rays or general DNA damage from desiccation in the built environment (42). The genes could also raise the stress threshold for the lysogenic to lytic transition, which may explain why our UV treatment was unable to elicit a lytic phenotype in the ight strains.…”