[A-OS11] Continental Oceanic Mutual Interaction - Planetary Scale Material Circulation

[AOS11-04] Comprehensive Evaluation of Artificial Structures on the Moon Considering Space Radiation Exposure

*Emika Fujii¹, Yosuke Alexandre Yamashiki¹, Tatsuhiko Sato² (1.Graduate School of Advanced Integrated Studies in Human Survivability Kyoto University, 2.Japan Atomic Energy Agency)

Keywords:Space radiation, Radiation exposure, Lunar structure

There are various barriers to the realization of human space exploration, of which cosmic radiation exposure is one of the major challenges. Especially on the lunar surface, where there is no atmosphere or magnetic field, the effects of cosmic radiation such as galactic cosmic rays and solar energetic particles are estimated to be significant. The purpose of this study is to quantify the possible exposure to cosmic radiation when artificial structures are constructed on the Moon in the future, and to summarize various possible components and their wall surfaces for space structures when the risk of exposure is set to be the same as that of habitation on Earth. At the same time, the assumed cost of transporting these components from Earth will also be discussed. First, the frequency of solar particle events (SPEs) that could have a negative impact on health was determined using data from the SOHO/ERNE satellite. The frequency of GLE (Ground Level Enhancement) 69, which has attracted attention as a particularly large SPE, is estimated to occur about once every 35 years, based on the frequency of events with a harder spectrum than GLE69 and a larger fluence of 1 MeV protons. The frequency was estimated to occur about once every 35 years. According to the results of ground-based observatories using ground-based neutron monitors, the probability of the occurrence of a SPE of about GLE69 is about once every 25-100 years, a result that is consistent with previous studies. Next, the PHITS code was used to simulate the dose inside a domed lunar base model when reproducing Galactic Cosmic Rays (GCR) and GLE69 during a normal solar active period. Six types of wall materials were used in three categories: (1) those containing boron (boron carbide and hydrogen boride sheets), (2) metals (aluminum alloy and magnesium alloy), and (3) resins (acrylic resin and polyethylene), with different wall thicknesses and combinations for each. The thicknesses of the walls were varied to ensure that the average dose inside the base did not exceed the effective dose limit allowed for occupational exposure and public exposure. The results showed that the single layer of the GCR reproduction was approximately 5 m or more, and the single and double layers of the GLE69 reproduction were several tens of centimeters. Finally, the cost of transporting these materials from the ground to the lunar surface was calculated. The results showed that the cost of transporting a single layer ranged from 700 to 2,150 trillion yen when the GCR was reproduced and from about 50 to 130 trillion yen when the GLE69 was reproduced, while the cost of transporting a double layer ranged from 26 to 63 trillion yen when the GLE69 was reproduced. In the case of GLE69, the cost of the multi-layered wall is 26 trillion yen to 63 trillion yen. In the case of one type of wall material, the transportation cost increases as the wall thickness and density increase, but in the case of two types of wall materials and an inner wall thickness between 5 cm and 50 cm, if the inner wall density is greater than the outer wall density, the cost increases as the inner wall becomes thicker and if the density of the inner wall is less than the density of the outer wall, the cost should decrease as the inner wall thickens. As described above, this study examined suitable wall materials based on simulation results for a lunar base structure effective for shielding against cosmic radiation, together with the perspective of transportation cost, which has rarely been discussed in academic literature, but there are some issues that remain to be addressed. For example, in the estimation of the probability of the occurrence of GLE69, data was not available due to the limitations of the detector, and data from the SOHO satellite did not show the maximum peak, even though the event should have had the maximum peak on the ground. This may be due to the fact that data from a satellite orbiting in an orbit unaffected by the Earth's magnetic field was used, which may not have adequately captured the same peaks as on the ground. Further study is needed on the relationship between the sensitivity of the detector in space and the neutron event peaks on the ground. In addition, since a thickness of several meters or more is required to shield the GCRs that fall daily to the same level as on the earth, it may be controversial to apply the effective dose limits allowed for occupational and public exposure on the earth to the moon. Based on this study, it is necessary to refine the simulation results of this study by setting more detailed conditions and selecting appropriate data.