- Email: [email protected]
Problems and conception of ensuring radiation safety during Mars missions
Advances in Space Research 34 (2004) 1451–1454 www.elsevier.com/locate/asr
Problems and conception of ensuring radiation safety during Mars missions V.M. Petrov
*
State Scientific Center – Institute of Biomedical Problems, Khoroshevskoye shosse, 76a, 123007 Moscow, Russia Received 20 June 2002; received in revised form 14 September 2002; accepted 21 September 2002
Abstract The Mars mission differs from near-Earth manned space flights by radiation environment and duration. The importance of effective using the weight of the spacecraft increases greatly because all the necessary things for the mission must be included in its starting weight. For this reason the development of optimal systems of radiation safety ensuring (RSES) acquires especial importance. It is the result of sharp change of radiation environment in the interplanetary space as compared to the one in the nearEarth orbits and significant increase of the interplanetary flight duration. The demand of a harder limitation of unfavorable factors effects should lead to radiation safety (RS) standards hardening. The main principles of ensuring the RS of the Mars mission (optimizing, radiation risk, ALARA) and the conception of RSES, developed on the basis of the described approach and the experience obtained during orbital flights are presented in the report. The problems that can impede the ensuring of the crew members’ RS are also given here. Published by Elsevier Ltd on behalf of COSPAR. Keywords: Mars mission; Space radiation; Safety system; Risk; Shielding
1. Introduction
2. Radiation environment during Mars mission
The radiation safety (RS) problem is of great importance during the piloted Mars mission. A significant change of the radiation environment in deep space as compared to the orbital flight conditions, a very considerable increase of mission duration and impossibility of terminating the flight in alarm situations cause it. Furthermore, the specificity of the Mars mission program due to considerable and long-continued stress of practically all the body systems will apparently demand a more harder limitation of the effects of the space flight unfavorable factors. Consequently, corresponding local limits including the radiation safety standards must become harder. The principles that can be used for ensuring the RS of the Mars mission and problems that can impede this kind of activity during the flight are given below.
On the basis of a large number of studies of space radiation environment (Hess, 1968; Dorman and Miroshnichenko, 1968; Miroshnichenko and Petrov, 1985) it can be concluded that all the three space radiation sources (Earth radiation belts (ERB), solar (SCR) and galactic (GCR) cosmic rays) will give input to the Mars mission crew’s exposure dose. However, the value of this input will vary depending on mission scenario. Radiation of the reactor or other nuclear power systems (if they are used on board the spacecraft) can give an additional input into the total radiation dose (Proceedings, 1972). The depth equivalent dose distribution in the body is of great importance for understanding the biological efficiency of irradiation. Calculated for the ‘‘Mir’’ station orbit (430 km altitude, 51.6 inclination) dependence of the GCR and ERB daily absorbed and equivalent doses on tissue thickness is given in Fig. 1. The calculation method was described by Kolomensky et al. (1998). This method was applied to calculation of values presented in Table 1. The GCR (GOST, 1991)
*
Tel.: +7-95-193-6595; fax: +7-95-193-6595. E-mail address: [email protected] (V.M. Petrov).
0273-1177/$30. Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2002.09.001
1452
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454
Fig. 1. ERB- and GCR-induced daily absorbed and equivalent doses versus aluminum shielding thickness in the MIR station orbit at the solar activity maximum (panel a) and minimum (panel b). Table 1 GCR doses, cSv, for 3 periods of solar activity depending on aluminum shielding thickness for the flight to Mars and back (435 days) Shielding thickness (g cm 2 )
Solar activity min.
Solar activity max.
Intermediate period
1 5 10 20
91.8 62.6 52.7 45.6
33.6 29.9 26.9 20.4
62.5 46.2 39.8 33.0
and ERB (Sawyer and Vette, 1976) models were used in dose calculations. The secondary component of cosmic radiation was taken into account as described in (RD, 1984; RD, 1985). It is seen that GCR daily absorbed and equivalent dose decreases when shielding thickness increases. Consequently, the radiobiological effects will be determined by irradiating the deeply placed organs of the man body because of its big dimensions. GCR in space are isotropic and their flux slightly changes within the period of 1–2 years. So, they can be qualified as a source of the crewmember’s chronic exposure. It is very important that LET spectrum of GCR determining their quality factor is very broad: from 3 MeV cm2 g 1 (for protons with an energy of 500 MeV) up to 1.5 · 103 MeV cm2 g 1 (for 86 Rn with an energy of 10 MeV/ nucleon). SCR are a stochastic source of ionizing radiation in space. SCR are generated by solar proton events (SPE), the theory of which has not been completed yet up to now (Stix, 1989). SPE duration can vary within the interval from some hours to some days and the total dose can vary within the range of some units to some thousands cSv depending on the strength of the event and sheilding parameters. The ERB dose is several cSv (when crossing them quickly) and varies depending on the flight trajectory. If astronauts cross the ERB in radiation shelter with shielding thickness of 30 g cm 2 , the total ERB dose will be equal to 1–2 cSv. We will use the upper value – 2 cSv – in our estimations of radiation exposure. It should be emphasized, that in all the
estimations a mean tissue dose is used (averaged per cosmonaut’s body). The estimations show that for the RS ensuring from GCR whole spacecraft shielding of fixed thickness is necessary. For reducing the SCR dose a small compartment with high wall thickness (radiation shelter) is necessary. Further, the following preconditions are adopted. The mission duration of the flight from Earth to Mars is 215 days, from Mars to Earth – 220 days, the period of stay on the Mars surface is 50,000 days. The shielding thickness on the Mars is determined by the atmosphere thickness and is equal to 10 g/cm2 . While calculating cosmic rays doses the shielding effect of the semi-space by the planet mass should be taken into account. This lessens the radiation dose two times. For describing GCR and SCR parameters widely used models of these radiation sources are used (GOST, 1991; GOST, 1986). The SCR are calculated for the distance from the Sun equal to 1 AU. This supposition leads to obtaining the upper dose values from SCR that increases the reliability of conclusions on the mission radiation safety. The calculations are performed for periods of minimum, maximum and medium levels of solar activity. The arithmetic mean of doses for minimum and maximum of solar activity was taken as a quantitative estimations for the period of its medium level. Table 1 presents the values of GCR doses in the interplanetary space for the crew depending on the aluminum radiation shielding thickness for the mentioned above solar cycle periods. Comparison of the calculated dose values with data presented by other authors (Dudkin and Potapov, 1992) demonstrates the satisfactory agreement in the limit of 20%. SCR will only give an input to the total radiation dose in the periods of intermediate, and maximum solar activity levels. The maximum input to the dose can be conditioned by ‘‘the most worst event’’. We defined this event as the one that gives behind the chosen shielding thickness the dose probability of which is equal to 10 4 . The SCR doses including the most worst event dose
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454 Table 2 SCR doses in the interplanetary space depending on shielding thickness for the period of 435 days, cSv
1453
Table 4 Total per mission crew dose values depending on the duration of staying on the Mars surface, cSv
Shielding thickness (g cm 2 )
Mean SCR dose
The most worse event dose
Staying (days)
SA min.
SA intermediate
SA max.
Russian dose limits
1 5 10 20 50
36.7 14.5 8.3 3.8 0.8
847 442 308 178 51
50 100 500
57.7 60.7 84.7
44.0 46.3 63.8
39.2 41.2 61.7
93.5 93.5 140
were calculated by the Monte-Carlo method. However, the frequency of such events (according to the observation data in the 19th, 20th and 21st cycles of solar activity) does not exceed one per 20–30 years. In addition, according to the condition mentioned above, we’ll believe that the radiation shelter permits to decrease the radiation dose of the crew to acceptable values in this case as well. Table 2 presents the most possible SCR doses depending on shielding thickness for the flight from Earth to Mars and back. Table 3 presents the doses of the crew’s irradiation on the Mars surface. As it was mentioned above we assumed that the planet body decreases the dose value of GCR and SCR two times. For estimating radiation hazard level we will compare the total dose values with the dose limits established for the flight under consideration, for example with those that are in force in Russia. For these estimations we will present total doses per mission when the adopted value of the effective thickness of shielding is 10 g cm 2 on all its stages with taking into account the ERB dose of 2 cSv (Table 4). It is seen from the table that the dose limits are not exceeded for all the versions of the Mars mission if the most worse event is absent. It means that the Mars mission is possible on the condition that modern radiation standards are used. However all reasonable measures for maximum decreasing the crew’s radiation doses should be taken.
3. Main principles of crew radiation safety ensuring Unfavorable effects from space radiation exposure are caused both by an absorbed dose and its LETspectrum, spatial and temporal distribution. However, decreasing radiation doses to values typical of ‘‘ground’’ occupations will demand such a large thickness of
shielding that is unreal for a space flight. So, while developing radiation standards the compromise between unfavorable consequences of the exposure and the possibility of carrying out the flight to Mars should be made. In other words, while developing dose standards the ALARA principle should be used (ICPR, 1990). As a quantitative measure of radiation hazard, at present a radiation risk that is the increase of a man’s death probability induced by his exposure, is used. The most important questions that should be solved while developing radiation standards for the Mars mission are – what medical and radiobiological effects and their quantitative models must be taken into account while defining the radiation risk. The uncertainty in the quantitative expression of these consequences especially for the delayed effects is one of the most important problems the solution of which is necessary for radiation safety of the Mars mission crew. More precise knowledge in this sphere will probably result in further hardening dose limits in general and in space application, in particular. One of the problems is the combined action of radiation and other space flight factors. Previous investigations have demonstrated that such a combined impact can change the radiobiological effect by 20– 30%, but it is not clear in which way the increase of flight duration can influence these estimations (Grigoriev et al., 1977). The problems of the spacecraft weight optimization result in finding out the solar cycle period for a better carrying out the mission. The estimations demonstrate that for minimizing the spacecraft weight, the flight should be carried out during the solar maximum, because the radiation shelter shielding can effectively decrease the SCR dose and the GCR flux and consequently, the dose will be two times less. The more accurate radiation shielding estimation can only be fulfilled for a specific mission scenario.
Table 3 Crew dose values depending on the duration of staying on the Mars surface, cSv Duration days
GCR dose, SA min.
GCR dose, SA intermediate
GCR dose, SA max.
Averaged SCR dose
Max. SCR dose
50 100 500
3.0 6.0 3.0
2.2 4.5 22.0
1.5 3.1 15.0
0.5 1.0 9.5
154 154 154
1454
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454
The list of problems for investigation includes: • estimating the efficiency of local shielding of body’s critical organs; • developing pharmacological means of radiation shielding, adequate to the irradiation in the interplanetary flight; • studying the crew members’ work capacity after the exposure. All the approaches and principles discussed above must be realized as a system of Mars mission RS ensuring. For all this the radiation monitoring system plays an important role, because besides having the function of measuring radiation dose of crew members, it has the function of forecasting radiation environment inside and outside the spacecraft, what is necessary for carrying out the protection measures in time (Petrov, 1997).
4. Conclusion In conclusion we will enumerate all the main issues that should be taken into account in the process of developing the RS system of the Mars mission crew. They are as follows: • A very high penetrating ability of GCR that can lead to a situation when the crew members’ exposure by this source is determinative and an adequate radiation shielding is necessary. • The existing uncertainty in the parameters of radiobiological effects induced in a man’s body by densely ionizing space radiation. • Tendency to continued hardening of standards in the world practice of RS ensuring. • Blanks in solar and space physics not permitting to obtain necessary reliability of SCR parameters forecasting. • Discrepancy of the existing chemical radiation protectors to exposure conditions of interplanetary flights. • Regularities of manifestation of combined impact of space radiation and other unfavorable factors of space flights. • Methodology of radiation shielding optimization with taken into account other elements of RS system of the mission crew. The main principle of optimization (ALARA) in radiation protection must be used while developing the
mission radiation safety system because of the necessity of optimal usage of the spacecraft weight. Modernization of RS quantitative criterion in the form of an integral index of the crew’s life ability (health and work capacity) most likely based on the probabilistic description of these values, can be necessary for the realization of this approach.
Acknowledgements Author thanks Dr. A. Kolomensky for help in doses calculation.
References Dorman, L.I., Miroshnichenko, L.I. Solar Cosmic Rays, Moscow, Nauka, p. 468, 1968. Dudkin, V.E., Potapov, Yu.V. Doses from galactic cosmic ray particles under spacecraft shielding. Nucl. Tracks Radiat. Meas. 20 (1), 33–39, 1992. Grigoriev, Yu.G., Drusinin, Yu.P., et al. Main goals and results of radiobiological experiment on board the biosatellite Kosmos-690. Space Biol. Med. Russian, 39, 1977. GOST, 25645. 150–90, The galactic cosmic rays. Model of changing of the particle fluxes. Moscow, Gosstandart, USSR, 1991. GOST 25645.134–86, Solar cosmic rays. Model of proton fluxes. Moscow, Gosstandart, USSR, 1986. Hess, W.N. The Radiation Belt and Magnitosphere. Blaisdell, Waltham, MA, 1968. ICPR Recommendations, 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, Pergamon Press, 1990. Kolomensky, A.V., Petrov, V.M., Shafirkin, A.V. Technique for determination of radiation effects in cosmonants on the basis of on-board dosimeter readings during orbital missions. Aviakosmicheskaya: Ecologicheskaya Meditsina (Russia) 32 (4), 44–49, 1998. Miroshnichenko, L.I., Petrov, V.M. Dynamics of radiation conditions in space. Energoatomisdat, Moscow, 1985, p. 149. Petrov, V.M. Present and future radiation dosimetry for Russian cosmonauts. Rad. Res. 148, s24–s32, 1997. Proceedings of the National Symposium on Natural and Manmade Radiation in Space, NASA TM X-2440, Washington, D.C., 1972. RD-50-25645.207-85. Calculation method of absorbed and equivalent dose for high Z particles of cosmic rays. Moscow, Gosstandart, USSR, 1985. RD-50-25645.208-84. Calculation method of absorbed and equivalent dose for protons of cosmic rays. Moscow Gosstandart, USSR, 1984. Sawyer, D.V., Vette, J.I. AP-8 Trapped Proton Environment for Solar Maximum and Minimum, NSSDS/WDS-A-R&S 76 06, 1976. Stix, M. The Sun. Springer-Verlag, New York, 1989, p. 360.
Problems and conception of ensuring radiation safety during Mars missions V.M. Petrov
*
State Scientific Center – Institute of Biomedical Problems, Khoroshevskoye shosse, 76a, 123007 Moscow, Russia Received 20 June 2002; received in revised form 14 September 2002; accepted 21 September 2002
Abstract The Mars mission differs from near-Earth manned space flights by radiation environment and duration. The importance of effective using the weight of the spacecraft increases greatly because all the necessary things for the mission must be included in its starting weight. For this reason the development of optimal systems of radiation safety ensuring (RSES) acquires especial importance. It is the result of sharp change of radiation environment in the interplanetary space as compared to the one in the nearEarth orbits and significant increase of the interplanetary flight duration. The demand of a harder limitation of unfavorable factors effects should lead to radiation safety (RS) standards hardening. The main principles of ensuring the RS of the Mars mission (optimizing, radiation risk, ALARA) and the conception of RSES, developed on the basis of the described approach and the experience obtained during orbital flights are presented in the report. The problems that can impede the ensuring of the crew members’ RS are also given here. Published by Elsevier Ltd on behalf of COSPAR. Keywords: Mars mission; Space radiation; Safety system; Risk; Shielding
1. Introduction
2. Radiation environment during Mars mission
The radiation safety (RS) problem is of great importance during the piloted Mars mission. A significant change of the radiation environment in deep space as compared to the orbital flight conditions, a very considerable increase of mission duration and impossibility of terminating the flight in alarm situations cause it. Furthermore, the specificity of the Mars mission program due to considerable and long-continued stress of practically all the body systems will apparently demand a more harder limitation of the effects of the space flight unfavorable factors. Consequently, corresponding local limits including the radiation safety standards must become harder. The principles that can be used for ensuring the RS of the Mars mission and problems that can impede this kind of activity during the flight are given below.
On the basis of a large number of studies of space radiation environment (Hess, 1968; Dorman and Miroshnichenko, 1968; Miroshnichenko and Petrov, 1985) it can be concluded that all the three space radiation sources (Earth radiation belts (ERB), solar (SCR) and galactic (GCR) cosmic rays) will give input to the Mars mission crew’s exposure dose. However, the value of this input will vary depending on mission scenario. Radiation of the reactor or other nuclear power systems (if they are used on board the spacecraft) can give an additional input into the total radiation dose (Proceedings, 1972). The depth equivalent dose distribution in the body is of great importance for understanding the biological efficiency of irradiation. Calculated for the ‘‘Mir’’ station orbit (430 km altitude, 51.6 inclination) dependence of the GCR and ERB daily absorbed and equivalent doses on tissue thickness is given in Fig. 1. The calculation method was described by Kolomensky et al. (1998). This method was applied to calculation of values presented in Table 1. The GCR (GOST, 1991)
*
Tel.: +7-95-193-6595; fax: +7-95-193-6595. E-mail address: [email protected] (V.M. Petrov).
0273-1177/$30. Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2002.09.001
1452
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454
Fig. 1. ERB- and GCR-induced daily absorbed and equivalent doses versus aluminum shielding thickness in the MIR station orbit at the solar activity maximum (panel a) and minimum (panel b). Table 1 GCR doses, cSv, for 3 periods of solar activity depending on aluminum shielding thickness for the flight to Mars and back (435 days) Shielding thickness (g cm 2 )
Solar activity min.
Solar activity max.
Intermediate period
1 5 10 20
91.8 62.6 52.7 45.6
33.6 29.9 26.9 20.4
62.5 46.2 39.8 33.0
and ERB (Sawyer and Vette, 1976) models were used in dose calculations. The secondary component of cosmic radiation was taken into account as described in (RD, 1984; RD, 1985). It is seen that GCR daily absorbed and equivalent dose decreases when shielding thickness increases. Consequently, the radiobiological effects will be determined by irradiating the deeply placed organs of the man body because of its big dimensions. GCR in space are isotropic and their flux slightly changes within the period of 1–2 years. So, they can be qualified as a source of the crewmember’s chronic exposure. It is very important that LET spectrum of GCR determining their quality factor is very broad: from 3 MeV cm2 g 1 (for protons with an energy of 500 MeV) up to 1.5 · 103 MeV cm2 g 1 (for 86 Rn with an energy of 10 MeV/ nucleon). SCR are a stochastic source of ionizing radiation in space. SCR are generated by solar proton events (SPE), the theory of which has not been completed yet up to now (Stix, 1989). SPE duration can vary within the interval from some hours to some days and the total dose can vary within the range of some units to some thousands cSv depending on the strength of the event and sheilding parameters. The ERB dose is several cSv (when crossing them quickly) and varies depending on the flight trajectory. If astronauts cross the ERB in radiation shelter with shielding thickness of 30 g cm 2 , the total ERB dose will be equal to 1–2 cSv. We will use the upper value – 2 cSv – in our estimations of radiation exposure. It should be emphasized, that in all the
estimations a mean tissue dose is used (averaged per cosmonaut’s body). The estimations show that for the RS ensuring from GCR whole spacecraft shielding of fixed thickness is necessary. For reducing the SCR dose a small compartment with high wall thickness (radiation shelter) is necessary. Further, the following preconditions are adopted. The mission duration of the flight from Earth to Mars is 215 days, from Mars to Earth – 220 days, the period of stay on the Mars surface is 50,000 days. The shielding thickness on the Mars is determined by the atmosphere thickness and is equal to 10 g/cm2 . While calculating cosmic rays doses the shielding effect of the semi-space by the planet mass should be taken into account. This lessens the radiation dose two times. For describing GCR and SCR parameters widely used models of these radiation sources are used (GOST, 1991; GOST, 1986). The SCR are calculated for the distance from the Sun equal to 1 AU. This supposition leads to obtaining the upper dose values from SCR that increases the reliability of conclusions on the mission radiation safety. The calculations are performed for periods of minimum, maximum and medium levels of solar activity. The arithmetic mean of doses for minimum and maximum of solar activity was taken as a quantitative estimations for the period of its medium level. Table 1 presents the values of GCR doses in the interplanetary space for the crew depending on the aluminum radiation shielding thickness for the mentioned above solar cycle periods. Comparison of the calculated dose values with data presented by other authors (Dudkin and Potapov, 1992) demonstrates the satisfactory agreement in the limit of 20%. SCR will only give an input to the total radiation dose in the periods of intermediate, and maximum solar activity levels. The maximum input to the dose can be conditioned by ‘‘the most worst event’’. We defined this event as the one that gives behind the chosen shielding thickness the dose probability of which is equal to 10 4 . The SCR doses including the most worst event dose
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454 Table 2 SCR doses in the interplanetary space depending on shielding thickness for the period of 435 days, cSv
1453
Table 4 Total per mission crew dose values depending on the duration of staying on the Mars surface, cSv
Shielding thickness (g cm 2 )
Mean SCR dose
The most worse event dose
Staying (days)
SA min.
SA intermediate
SA max.
Russian dose limits
1 5 10 20 50
36.7 14.5 8.3 3.8 0.8
847 442 308 178 51
50 100 500
57.7 60.7 84.7
44.0 46.3 63.8
39.2 41.2 61.7
93.5 93.5 140
were calculated by the Monte-Carlo method. However, the frequency of such events (according to the observation data in the 19th, 20th and 21st cycles of solar activity) does not exceed one per 20–30 years. In addition, according to the condition mentioned above, we’ll believe that the radiation shelter permits to decrease the radiation dose of the crew to acceptable values in this case as well. Table 2 presents the most possible SCR doses depending on shielding thickness for the flight from Earth to Mars and back. Table 3 presents the doses of the crew’s irradiation on the Mars surface. As it was mentioned above we assumed that the planet body decreases the dose value of GCR and SCR two times. For estimating radiation hazard level we will compare the total dose values with the dose limits established for the flight under consideration, for example with those that are in force in Russia. For these estimations we will present total doses per mission when the adopted value of the effective thickness of shielding is 10 g cm 2 on all its stages with taking into account the ERB dose of 2 cSv (Table 4). It is seen from the table that the dose limits are not exceeded for all the versions of the Mars mission if the most worse event is absent. It means that the Mars mission is possible on the condition that modern radiation standards are used. However all reasonable measures for maximum decreasing the crew’s radiation doses should be taken.
3. Main principles of crew radiation safety ensuring Unfavorable effects from space radiation exposure are caused both by an absorbed dose and its LETspectrum, spatial and temporal distribution. However, decreasing radiation doses to values typical of ‘‘ground’’ occupations will demand such a large thickness of
shielding that is unreal for a space flight. So, while developing radiation standards the compromise between unfavorable consequences of the exposure and the possibility of carrying out the flight to Mars should be made. In other words, while developing dose standards the ALARA principle should be used (ICPR, 1990). As a quantitative measure of radiation hazard, at present a radiation risk that is the increase of a man’s death probability induced by his exposure, is used. The most important questions that should be solved while developing radiation standards for the Mars mission are – what medical and radiobiological effects and their quantitative models must be taken into account while defining the radiation risk. The uncertainty in the quantitative expression of these consequences especially for the delayed effects is one of the most important problems the solution of which is necessary for radiation safety of the Mars mission crew. More precise knowledge in this sphere will probably result in further hardening dose limits in general and in space application, in particular. One of the problems is the combined action of radiation and other space flight factors. Previous investigations have demonstrated that such a combined impact can change the radiobiological effect by 20– 30%, but it is not clear in which way the increase of flight duration can influence these estimations (Grigoriev et al., 1977). The problems of the spacecraft weight optimization result in finding out the solar cycle period for a better carrying out the mission. The estimations demonstrate that for minimizing the spacecraft weight, the flight should be carried out during the solar maximum, because the radiation shelter shielding can effectively decrease the SCR dose and the GCR flux and consequently, the dose will be two times less. The more accurate radiation shielding estimation can only be fulfilled for a specific mission scenario.
Table 3 Crew dose values depending on the duration of staying on the Mars surface, cSv Duration days
GCR dose, SA min.
GCR dose, SA intermediate
GCR dose, SA max.
Averaged SCR dose
Max. SCR dose
50 100 500
3.0 6.0 3.0
2.2 4.5 22.0
1.5 3.1 15.0
0.5 1.0 9.5
154 154 154
1454
V.M. Petrov / Advances in Space Research 34 (2004) 1451–1454
The list of problems for investigation includes: • estimating the efficiency of local shielding of body’s critical organs; • developing pharmacological means of radiation shielding, adequate to the irradiation in the interplanetary flight; • studying the crew members’ work capacity after the exposure. All the approaches and principles discussed above must be realized as a system of Mars mission RS ensuring. For all this the radiation monitoring system plays an important role, because besides having the function of measuring radiation dose of crew members, it has the function of forecasting radiation environment inside and outside the spacecraft, what is necessary for carrying out the protection measures in time (Petrov, 1997).
4. Conclusion In conclusion we will enumerate all the main issues that should be taken into account in the process of developing the RS system of the Mars mission crew. They are as follows: • A very high penetrating ability of GCR that can lead to a situation when the crew members’ exposure by this source is determinative and an adequate radiation shielding is necessary. • The existing uncertainty in the parameters of radiobiological effects induced in a man’s body by densely ionizing space radiation. • Tendency to continued hardening of standards in the world practice of RS ensuring. • Blanks in solar and space physics not permitting to obtain necessary reliability of SCR parameters forecasting. • Discrepancy of the existing chemical radiation protectors to exposure conditions of interplanetary flights. • Regularities of manifestation of combined impact of space radiation and other unfavorable factors of space flights. • Methodology of radiation shielding optimization with taken into account other elements of RS system of the mission crew. The main principle of optimization (ALARA) in radiation protection must be used while developing the
mission radiation safety system because of the necessity of optimal usage of the spacecraft weight. Modernization of RS quantitative criterion in the form of an integral index of the crew’s life ability (health and work capacity) most likely based on the probabilistic description of these values, can be necessary for the realization of this approach.
Acknowledgements Author thanks Dr. A. Kolomensky for help in doses calculation.
References Dorman, L.I., Miroshnichenko, L.I. Solar Cosmic Rays, Moscow, Nauka, p. 468, 1968. Dudkin, V.E., Potapov, Yu.V. Doses from galactic cosmic ray particles under spacecraft shielding. Nucl. Tracks Radiat. Meas. 20 (1), 33–39, 1992. Grigoriev, Yu.G., Drusinin, Yu.P., et al. Main goals and results of radiobiological experiment on board the biosatellite Kosmos-690. Space Biol. Med. Russian, 39, 1977. GOST, 25645. 150–90, The galactic cosmic rays. Model of changing of the particle fluxes. Moscow, Gosstandart, USSR, 1991. GOST 25645.134–86, Solar cosmic rays. Model of proton fluxes. Moscow, Gosstandart, USSR, 1986. Hess, W.N. The Radiation Belt and Magnitosphere. Blaisdell, Waltham, MA, 1968. ICPR Recommendations, 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, Pergamon Press, 1990. Kolomensky, A.V., Petrov, V.M., Shafirkin, A.V. Technique for determination of radiation effects in cosmonants on the basis of on-board dosimeter readings during orbital missions. Aviakosmicheskaya: Ecologicheskaya Meditsina (Russia) 32 (4), 44–49, 1998. Miroshnichenko, L.I., Petrov, V.M. Dynamics of radiation conditions in space. Energoatomisdat, Moscow, 1985, p. 149. Petrov, V.M. Present and future radiation dosimetry for Russian cosmonauts. Rad. Res. 148, s24–s32, 1997. Proceedings of the National Symposium on Natural and Manmade Radiation in Space, NASA TM X-2440, Washington, D.C., 1972. RD-50-25645.207-85. Calculation method of absorbed and equivalent dose for high Z particles of cosmic rays. Moscow, Gosstandart, USSR, 1985. RD-50-25645.208-84. Calculation method of absorbed and equivalent dose for protons of cosmic rays. Moscow Gosstandart, USSR, 1984. Sawyer, D.V., Vette, J.I. AP-8 Trapped Proton Environment for Solar Maximum and Minimum, NSSDS/WDS-A-R&S 76 06, 1976. Stix, M. The Sun. Springer-Verlag, New York, 1989, p. 360.