Viktor Georgievich Mitrikas, Chief Researcher at the Institute of Biomedical Research of the Russian Academy of Sciences (IMBP RAS), analyzed the degree of radiation exposure to various organs and tissues of the ISS cosmonauts who visited the station from 2001 to 2021. According to the results, for 20 years, not a single space flight has exceeded the established radiation safety standards.
The press service of the Institute of Biomedical Problems of the Russian Academy of Sciences handed over the research materials to the information service. According to the scientific work, data were collected on sensors installed in a special robot (torso phantom) and on personal dosimeters of astronauts. Inside the phantom there is a set of sensors that collect various data to simulate the impact of the environment on various human organs. The robot was located in three places inside the ISS service module: a large diameter working compartment (ROBD), a small diameter working compartment (ROMD) and a port side cabin (LB).
In the case of the astronauts, personal dosimeters ID3-MKS based on thermoluminescent glasses were used in the measurements. However, the devices allow you to control only the absorbed dose of radiation exposure to the astronauts' skin. The crew must wear dosimeters at all times, and, as analysis of the measurements shows, not all astronauts followed this rule. This is clearly seen in the comparison table below.
Judging by the significant difference in performance, cosmonauts 1, 3, 4, 12, 13, 20, and 23 did not constantly wear individual dosimeters. They could leave them in some compartments of the ISS. In particular, in the functional cargo unit (FGB), the absorbed dose rate is on average 66% of the absorbed dose rate in the ROBD. Also, for cosmonauts 5, 40, 41, 62, 63, 64 and 65, the calculated value of the absorbed dose is less than the experimental values, which may be due to the predominant stay of these crew members in small modules, where the absorbed dose rate is on average 40–45% higher than in ROBD. Sometimes the difference in doses reached values of 90-130%. They could also leave dosimeters in the Soyuz, where radiation protection is weaker than in the ISS. Depending on the placement of the dosimeter, the absorbed dose rate is 160-245% of the dose rate in the ROBD.
The values significantly depended on the duration of the space flight and the phase of the solar activity cycle (on average, astronauts stay on the ISS for about 10 days). It was also necessary to take into account the individual schedule of each flight participant and the time of visiting the modules. For example, in the Japanese Kibo module, the average daily absorbed dose rate is 1.5–1.6 times higher than in the service module. In Russian small modules, this figure is 1.2–1.5 times higher than in the service module. In the FGB and the American Harmony module, it is 0.6–0.8 of the power in the service module. If these discrepancies are not taken into account, the use of average characteristics can lead to critical errors in estimates of the levels of radiation exposure to crew members.
The calculations also take into account the difference in doses received when staying at the station, performing work in open space, and approaching the manned transport spacecraft from the ISS. But these works make up fractions of a percent of the total duration of the expedition. Solar proton events (SPEs) were also taken into account, while Viktor Georgievich noted that in none of the 66 expeditions to the ISS, the contribution of SPE protons did not exceed 1%. Only in 5 expeditions it was more than 0.5%.
According to the standard regime of work and rest for cosmonauts, from 21.30 (flight time) to 6.00 the crew is in the KLB, the rest of the time - mainly in the ROBD and ROMD. Additional time is allocated for crew change, cargo ship docking and extravehicular activities. Based on the graph, two types of calculations were carried out. In the first one, the absorbed dose in the CLB was determined only at night, in the ROBD and ROMD - only in the daytime. In the second variant, the resulting dose was equal to the sum of the daily doses at each place of stay, divided by three.
According to the results of the study, for 20 years of flights to the ISS, none of the expeditions exceeded the established radiation safety standards. For a flight lasting 30 days, the limiting dose of radial radiation is 150 mSv (millisievert), for a one-year flight - 300 mSv. For intermediate flight duration, linear interpolation is used.
The table below shows the results of calculating the effective dose and equivalent doses for QOL (skin), CG (eye lens) and CTS (hematopoietic system). As indicated in the paper, the calculations were originally made for RSC Energia, but in they were not needed, since the sanitary and epidemiological supervision during the preparation and conduct of space flights was transferred to the Federal Medical and Biological Agency (FMBA). At the same time, the author points out that he is not aware of the receipt of requests from the FMBA for calculations of the effective doses received by astronauts.
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