[ESTIMATION OF IONIZING RADIATION EFFECTIVE DOSES IN THE INTERNATIONAL SPACE STATION CREWS BY THE METHOD OF CALCULATION MODELING].

Monitoring of the radiation loading on cosmonauts requires calculation of absorbed dose dynamics with regard to the stay of cosmonauts in specific compartments of the space vehicle that differ in shielding properties and lack means of radiation measurement. The paper discusses different aspects of calculation modeling of radiation effects on human body organs and tissues and reviews the effective dose estimates for cosmonauts working in one or another compartment over the previous period of the International space station operation. It was demonstrated that doses measured by a real or personal dosimeters can be used to calculate effective dose values. Correct estimation of accumulated effective dose can be ensured by consideration for time course of the space radiation quality factor.

[Mathematical simulation support to the dosimetric monitoring on the Russian segment of the International Space Station].

To ensure radiation safety of cosmonauts, it is necessary not only to predict, but also to reconstruct absorbed dose dynamics with the knowledge of how long cosmonauts stay in specific space vehicle compartments with different shielding properties and lacking equipment for dosimetric monitoring. In this situation, calculating is one and only way to make a correct estimate of radiation exposure of cosmonaut's organism as a whole (tissue-average dose) and of separate systems and organs. The paper addresses the issues of mathematical simulation of epy radiation environment of standard dosimetric instruments in the Russian segments of the International Space Station (ISS RS). Results of comparing the simulation and experimental data for the complement of dosimeters including ionization chamber-based radiometer R-16, DB8 dosimeters composed of semiconductor detectors, and Pille dosimeters composed of thermoluminescent detectors evidence that the current methods of simulation in support of the ISS RS radiation monitoring provide a sufficiently good agreement between the calculated and experimental data.

[Results of statistical analysis of the dynamics of ionizing radiation dose fields in the service module of the International Space Station in 2000-2012].

The on-going 24th solar cycle (SC) is distinguished from the previous ones by low activity. On the contrary, levels of proton fluxes from galactic cosmic rays (GCR) are high, which increases the proton flow striking the Earth's radiation belts (ERB). Therefore, at present the absorbed dose from ERB protons should be calculated with consideration of the tangible increase of protons intensity built into the model descriptions based on experimental measurements during the minimum between cycles 19 and 20, and the cycle 21 maximum. The absorbed dose from GCR and ERB protons copies galactic protons dynamics, while the ERB electrons dose copies SC dynamics. The major factors that determine the absorbed dose value are SC phase, ISS orbital altitude and shielding of the dosimeter readings of which are used in analysis. The paper presents the results of dynamic analysis of absorbed doses measured by a variety of dosimeters, namely, R-16 (2 ionization chambers), DB8-1, DB8-2, DB8-3, DB8-4 as a function of ISS orbit altitude and SC phase. The existence of annual variation in the absorbed dose dynamics has been confirmed; several additional variations with the periods of 17 and 52 months have been detected. Modulation of absorbed dose variations by the SC and GCR amplitudes has been demonstrated.

[Spatial distribution of local absorbed doses inside the Russian segment of the International Space Station].

The article discusses the procedure of operational radiation safety monitoring with the use of portable Pille-MKS dosimeters, presents the results of ISS dose measurements from September 22, 2003 (after Pille deployment on board the ISS) to March 16, 2011 (completion of the ISS-25 mission). The necessity of continuous dynamic tracking of the radiation environment in ISS compartments arises from the character and uniqueness of space ionizing radiation effects on crew. Radiation loading in the ISS compartments was analyzed and results of using different dosimeters were compared. Experimental radiation studies of the ISS piloted compartments are needed for reliable prediction of doses for the crew that still defy precise estimation.

[Effect of the ISS Russian segment configuration on the service module radiation environment].

Mathematical modeling of variations in the Service module radiation environment as a function of ISS Russian segment configuration was carried out using models of the RS modules and a spherical humanoid phantom. ISS reconfiguration impacted significantly only the phantom brought into the transfer compartment (ExT). The Radiation Safety Service prohibition for cosmonauts to stay in this compartment during solar flare events remains valid. In all other instances, error of dose estimation is higher as compared to dose value estimation with consideration for ISS RS reconfiguration.

[Radiation effect on cosmonauts during extravehicular activities in 2008-2009].

The geometrical model of suited cosmonaut's phantom was used in mathematical modeling of EVAs performed by cosmonauts with consideration of changes in the ISS Russian segment configuration during 2008-2009 and the dependence of space radiation absorbed dose on EVA scene. Influence of spatial position of cosmonaut on absorbed dose value was evaluated with the EVA dosimeter model reproducing the actually determined weight and dimension. Calculated absorbed dose values are in good agreement with experimental data. Absorbed doses imparted to body organs (skin, lens, hemopoietic system, gastrointestinal tract, central nervous system, gonads) were determined for specific EVA events.

[Dose loads on and radiation risk values for cosmonauts on a mission to Mars estimated from actual Martian vehicle engineering development].

The current design philosophy of a Mars orbiting vehicle, takeoff and landing systems and the transport return vehicle was taken into consideration for calculating the equivalent doses imparted to cosmonaut's organs and tissues by galactic cosmic rays, solar rays and the Earth's radiation belts, values of the total radiation risk over the lifespan following the mission and over the whole career period, and possible shortening of life expectancy. There are a number of uncertainties that should be evaluated, and radiation limits specified before setting off to Mars.

[Estimation of radiation loads on cosmonauts of the International Space Station during 2000 - 2007].

Radiation loads on cosmonauts during the initial 15 increments of the International space station (ISS) were analyzed with the use of a human body geometry model. The total characteristic of absorbed and equivalent doses in compartments of the ISS Russian segment was determined with consideration of the actual cosmophysical situation and ISS ballistic parameters during every increment in the period from October 2000 to October 2007.

[Estimation of effective and mean tissue doses on the ISS].

Complementing the earlier published geometric model of human body with description of the visceral organs gave an opportunity to define coordinates boundaries and compute volumes and masses of these organs. The paper presents the results of calculating the effective and mean tissue doses in the human body geometric model at the working station inside the large diameter compartment of the service module by the example of ISS increment 8. The calculated doses for quiescent and disturbed radiation environment are compared.

[Calculation of radiation loads onto cosmonauts during extravehicular activities on the International space station].

A geometrical spacesuit model was developed to assess shielding functions of the human body systems and organs. The shielding functions of specific points inside the spacesuit determined with the help of the geometric human body model were compared with the published data from experiments with the Russian Orlan-M spacesuit. Provided a good agreement of the results, shielding of specific organs and systems within the human body geometrical model were calculated. Periods of the ISS EVAs in the Russian spacesuits during 2001-2006 were analyzed to estimate the absorbed doses and quality factor for the body organs and systems. Methods for calculating the absorbed doses from the data of EVA dosimeters are proposed.

[The model of geometrical human body phantom for calculating tissue doses in the service module of the International Space Station].

The model of a geometrical human body phantom developed for calculating the shielding functions of representative points of the body organs and systems is similar to the anthropomorphic phantom. This form of phantom can be integrated with the shielding model of the ISS Russian orbital segment to make analysis of radiation loading of crewmembers in different compartments of the vehicle. Calculation of doses absorbed by the body systems in terms of the representative points makes it clear that doses essentially depend on the phantom spatial orientation (eye direction). It also enables the absorbed dose evaluation from the shielding functions as the mean of the representative points and phantom orientation.

[Some results of radiaton monitoring of the ISS Russian Segment in 2000-2005].

Dynamics of the ISS RS radiation environment was studied using the data of daily (operative) monitoring and personal dose measurements during 11 increments in the period between August 1, 2000 and October 28, 2005 overlapping the maximum phase of the 23rd solar cycle. It was shown that personal absorbed doses varied within the range of measurements of dual wavelength radiometer R-16, a component of the ISS radiation monitoring system. Power of the absorbed doses fell in the range of 0.017 to 0.02 cGy/day and was solar-dependent.

[A model of protectability of the ISS service module habitable compartments for radiation risk assessment]. / Model' zashchischchennosti obitaemykh otsekov sluzhebnogo modulia Mezhdunarodnoi kosmicheskoi stantsii dlia otsenki radiatsionnoi opasnosti.

A geometric model of the International space station (ISS) service module has been built up with account of basic structural components and spatial heterogeneity of matter distribution in SM equipment for the purpose of evaluating influence of a selected matter distribution function on the R-16 absorbed dose estimation. The uniform matter distribution function was shown to give the absorbed dose upper bound. Correspondingly, equipment representation as a homogeneous average density matter gives the absorbed dose lower bound. The best results were achieved using the normal law (Gauss law) for the matter distribution function. Shielding functions for DB-8 detectors (new radiation monitoring system elements) are presented.

[The assessment of radiation hazards in the "MIR" and ISS orbits from the data of vehicle and personal dosimetric monitoring]. / Otsenka radiatsionnoi opasnosti dlia chlenov ékipazhei orbital'noi stantsii "Mir" i Mezhdunarodnoi kosmicheskoi stantsii na osnove dannykh bortovogo i individual'nogo dozimetricheskogo kontrolia.

The paper describes the procedure of estimating total radiation risk to crewmembers during lifetime and possible lifetime reduction in consequence of participation in the Mir and ISS missions in different periods of the solar activity. The procedure includes analysis of data of vehicle and personal dosimetry, and calculations of radiation doses in various Mir compartments and accumulated by body tissues of cosmonauts. Calculated doses showed good consistency with the doses measured with R-16 on board Mir and personal dosimeters. To a first approximation, estimation of doses to cosmonauts and radiation risk as a result of participation in ISS missions took into account similarity of the Mir and ISS basal modules (geometry, dimensions and mass values) and was performed with the use of the space station shielding model that had been described elsewhere. The model of ISS radiation shielding will be updated as data of dosimetry of ISS compartments and phantom studies are available.

[Radiation environment of orbital complex "Mir" during minimum of the 22-nd solar cycle (1994-1996)]. / Radiatsionnaia obstanovka na orbital'nom komplekse "Mir" na faze minimuma 22-go tsikla solnechnoi aktivnosti (s 1994 po 1996 god).

Analysis of radiation dynamics on board the orbital complex MIR in the period of 1994 through to 1996 overlapping minimum of the 22nd solar cycle (SC) was performed. Radiation parameters in the working compartments during eight MIR missions (MIR 15-22) were evaluated. According to the solar dynamics during minimal activity with the lowest meanings of Wolf numbers (< 20), the daily average dose rate on MIR reached its peak over the whole 22nd SC and by a factor of more than three exceeded meanings typical for solar maximum. A statistical method was used to compute correlation coefficients and set up an equation of linear regression of the absorbed dose with cosmophysical parameters of the SC minimum. Meanings of the correlation coefficients for SC minimum were substantially lower as compared with SC maximum, that is there was no distinct correlation between dose rate and the parameters under study. Radiation doses to cosmonauts violated the admissible radiation limits for ground exposures but not radiation limits established for manned space missions. Reduction of dose loading on cosmonauts during SC minimum can be achieved by planning shorter missions or utilization of a program of radiation protection for traverse of SAA ERB.

[Variations of solar activity and radiation situation on board MIR station during the period 1986-1994]. / Variatsii solnechnoi aktivnosti i radiatsionnaia obstanovka na kosmicheskoi stantsii "Mir" v period s 1986 po 1994 gg.

This paper is dedicated to the analysis of the radiation situation onboard Mir station over a period of 1986-1994, there examined the main cosmophysics parameters and indices of the solar activity as well as the variations of the parameters of the earth's magnetic field and their association with the changes in the power of absorbed dose onboard the station. There noted the high levels of radiation exposure to the cosmonauts under terrestrial conditions when carrying out the roentgeno-radiologic examinations and procedures comparable or exceeding the absorbed doses during the flights. For revealing the regular associations of the radiation situation onboard the station with the parameters of solar activity there has been analyzed the time changes of average monthly values of dose power since the beginning of station functioning in 1986 until returning the fifteenth expedition to Earth. From the analyses of the results it might be assumed that the best statistical associations of average monthly power of the absorbed dose are found with the streams of protons of GCR. Wolff numbers and background stream of the radio emission of the Sun which reflects the existence of the radiation situation upon the phase of solar activity cycle. From this paper it transpires that calculating the dose loads during the period of the extreme phases of solar activity, it is possible to make between them the interpolations of time dependence by analogy with the dynamics in time of the background streams of GCR or Wolff numbers.

Radiation risk of the crew members of the expeditions on the "MIR" station during the 22nd solar activity cycle.

The radiation risk at the end of the flight was calculated for the members of the main expeditions on the "Mir" station. It was based on the absorbed dose dynamics data measured by the board dosimeter. The radiation damage models created for standards of the radiation safety of the space flights were used in the calculations. The analysis of the obtained values of the risk and its dynamics for some cosmonauts are presented in the topic. The risk values delta P are close to the limited levels given by equation of delta P = 0.6 x 10 x T(-4), [this equation appears also as delta RHrad = 0.6 x 10(-4) x T later in the text] where T--is flight duration in months.