Variations of the radiation dose onboard Mir station

Dose variations, associated with the 11-year solar activity cycle, seasonal variations of particle fluxes in the Earth's radiation belts at the station orbit, and solar proton events are studied, using prolonged measurements of radiation doses inside orbital station Mir. Daily averages of radiation doses during the declining phase of the 22^nd solar cycle and during transition to the 23^rd solar activity cycle reached very large values for astronauts and significantly exceed the values calculated according to existing models.     

Direct comparison of transient radiation belt topology and dynamics in 1991 based on measurements onboard Mir space station and NOAA satellite.

In March 1991 the CRRES spacecraft measured a new transient radiation belt resulting from a solar proton event and subsequent geomagnetic disturbance. The presence of this belt was also noted by dosimeter-radiometers aboard the Mir space station (approx. 400 km, 51 degrees orbit) and by particle telescopes on the NOAA-10 spacecraft (850 km, 98 degrees). This event provides a unique opportunity to compare particle flux and dose measurements made by different instruments in different orbits under changing conditions. We present here a comparison of the measurements made by the different detectors. We discuss the topology and dynamics of the transient radiation belt over a period of more than one year.     

Decay rate of the second radiation belt.

Variations in the Earth's trapped (Van Allen) belts produced by solar flare particle events are not well understood. Few observations of increases in particle populations have been reported. This is particularly true for effects in low Earth orbit, where manned spaceflights are conducted. This paper reports the existence of a second proton belt and it's subsequent decay as measured by a tissue-equivalent proportional counter and a particle spectrometer on five Space Shuttle flights covering an eighteen-month period. The creation of this second belt is attributed to the injection of particles from a solar particle event which occurred at 2246 UT, March 22, 1991. Comparisons with observations onboard the Russian Mir space station and other unmanned satellites are made. Shuttle measurements and data from other spacecraft are used to determine that the e-folding time of the peak of the second proton belt. It was ten months. Proton populations in the second belt returned to values of quiescent times within eighteen months. The increase in absorbed dose attributed to protons in the second belt was approximately 20%. Passive dosimeter measurements were in good agreement with this value.     

"Mir" radiation dosimetry results during the solar proton events in September-October 1989.

Using data from dosimetry-radiometry system "Liulin" on board of "Mir"-space station the particle flux and doserate during September-October, 1989 has been studied. The orbit of the station was 379 km perigee, 410 km apogee and 51.6 degrees inclination. Special attention has been paid to the flux and doserate changes inside the station after intensive solar proton events (SPE) on 29 of September, 1989. The comparison between the doses before and after the solar flares shows increase of the calculated mean dose per day by factor of 10 to 200. During the SPE on the 29 of September the additional dose was 310 mrad. The results of the experiment are compared with the data for the solar proton fluxes obtained on the GOES-7 satellite.     

Modeling of the radiation exposure during the flight of the second Bulgarian cosmonaut on board the Mir Space Station.

An experiment involving active detection of space radiation was carried out in the Space Research Institute (SRI) of Bulgarian Academy of Sciences, in preparation of the flight of the second Bulgarian cosmonaut. The radiations that would be encountered on the flight were modelled including solar and galactic cosmic rays and the particle radiation in the Earth's radiation belts. The dose rate was calculated for these different radiations behind the shielding of the space station. The variations in dose rates over the period of the flight were calculated and compared with measurements made during the orbit of the Mir Space Station. The calculated and measured dose rates agreed within 15-35%.     

太阳活动突发过程对临近空间大气影响的模拟

空间天气对地球及近地空间具有重要影响,大的空间天气事件对中上层大气动力学和成分具有不同的影响。利用全大气耦合模式WACCM,针对太阳耀斑、太阳质子、地磁暴三类事件,以太阳活动平静期2015年5月10-14日的GEOS-5数据为模式背景场,通过F_10.7、离子产生率、Kp及Ap指数设置,分别模拟三类事件对临近空间大气温度、密度和臭氧的影响。结果表明耀斑事件在三类事件中对临近空间大气温度和密度的影响最为显著。平流层大气温度增加是由耀斑辐射增强引起平流层臭氧吸收紫外辐射发生的光化学反应所致,耀斑事件引起平流层和低热层温度增加约为2～3 K,低热层大气相对密度增加在6%以内;太阳质子事件及磁暴事件主要影响低热层,但太阳质子事件和磁暴事件对低热层温度扰动不大于1 K。     

Analysis of the space radiation doses obtained simultaneously at two different locations outside the ISS

Space weather and related ionizing radiation has been recognized as one of the main health concerns for the International Space Station (ISS) crew. The estimation of the radiation effect on humans outside the ISS requires at first order accurate knowledge of their accumulated absorbed dose rates, which depend on the global space radiation distribution, solar cycle and local variations generated by the 3D mass distribution surrounding the ISS. The R3DE (Radiation Risks Radiometer-Dosimeter for the EXPOSE-E platform) on the European Technological Exposure Facility (EuTEF) worked successfully outside of the European Columbus module between February 2008 and September 2009. A very similar instrument named R3DR for the EXPOSE-R platform worked outside the Russian Zvezda module of the ISS between March 2009 and August 2010. Both are Liulin-type detectors, Bulgarian-built miniature spectrometer-dosimeters. The acquired approximately 5 million deposited energy spectra from which the flux and absorbed dose rate were calculated with 10 s resolution behind less than 0.41 g cm⁻² shielding. This paper analyses the spectra collected in 2009 by the R3DE/R instruments and the long-term variations in the different radiation environments of Galactic Cosmic Rays (GCR), inner radiation belt trapped protons in the region of the South Atlantic Anomaly (SAA) and relativistic electrons from the Outer Radiation Belt (ORB). The R3DE instrument, heavily shielded by the surrounding structures, measured smaller primary fluxes and dose rates from energetic protons from the SAA and relativistic electrons from the ORB but higher values from GCRs because of the contribution from secondary particles. The main conclusion from this investigation is that the dose rates from different radiation sources around the International Space Station (ISS) have a large special and temporal dynamic range. The collected data can be interpreted as possible doses obtained by the cosmonauts and astronauts during Extra Vehicular Activities (EVA) because the R3DE/R instruments shielding is very similar to the Russian and American space suits average shielding (,  and ). Fast, active measurements are required to assess accurately the dose accumulated by astronauts during EVA.     

SEP events and multi-spacecraft observations: Constraints on theory

Fifteen solar energetic particle (SEP) events have been analyzed using proton flux data recorded by the Helios 1, Helios 2, and IMP 8 spacecraft in the energy range ∼4–40 MeV during 1974–1982. For each of the events at least two of the spacecraft have their nominal magnetic footpoint within 20° in heliocentric longitude from each other. The SEP events are sub-grouped as a function of their heliocentric longitudinal separation and heliocentric radial distance from the SEP associated solar flare and several case studies are presented in this paper. Main results concerning their usage in estimating the SEP radial dependence are given. Moreover, we investigate the behavior of the third not connected spacecraft in order to study the dependence of the proton flux as a function of flare location. It is found that the contribution of the longitudinal gradient in determining variations in the SEP proton flux is particularly relevant for spacecraft having their magnetic connection footpoint separated from the flare between 30° and 50°.     

Cosmic ray variations of solar origin in relation to human physiological state during the December 2006 solar extreme events

There is an increasing amount of evidence linking biological effects to solar and geomagnetic disturbances. A series of studies is published referring to the changes in human physiological responses at different levels of geomagnetic activity. In this study, the possible relation between the daily variations of cosmic ray intensity, measured by the Neutron Monitor at the Cosmic Ray Station of the University of Athens (http://cosray.phys.uoa.gr) and the average daily and hourly heart rate variations of persons, with no symptoms or hospital admission, monitored by Holter electrocardiogram, is considered. This work refers to a group of persons admitted to the cardiological clinic of the KAT Hospital in Athens during the time period from 4th to 24th December 2006 that is characterized by extreme solar and geomagnetic activity. A series of Forbush decreases started on 6th December and lasted until the end of the month and a great solar proton event causing a Ground Level Enhancement (GLE) of the cosmic ray intensity on 13th December occurred. A sudden decrease of the cosmic ray intensity on 15th December, when a geomagnetic storm was registered, was also recorded in Athens Neutron Monitor station (cut-off rigidity 8.53 GV) with amplitude of 4%. It is noticed that during geomagnetically quiet days the heart rate and the cosmic ray intensity variations are positively correlated. When intense cosmic ray variations, like Forbush decreases and relativistic proton events produced by strong solar phenomena occur, cosmic ray intensity and heart rate get minimum values and their variations, also, coincide. During these events the correlation coefficient of these two parameters changes and follows the behavior of the cosmic ray intensity variations. This is only a small part of an extended investigation, which has begun using data from the year 2002 and is still in progress.     

Tissue equivalent detector data obtained recently on Mir space station. Comparison with Solid State Detector data

Tissue equivalent and Solid State Detector (SSD) measurements of the radiation environment inside the Mir space station were performed during the Antares mission in 1992 and long period after it. Interesting results about radiation measurements show (a) the South Atlantic Anomaly (SAA) crossing, (b) the increase of radiation near the poles and (c) the effects of solar eruptions (the most important one occurring in early November 1992). These data give also information about the dose and the quality factor of the radiation received by the cosmonauts during different missions.     

Human exposure to large solar particle events in space.

Whenever energetic solar protons produced by solar particle events traverse bulk matter, they undergo various nuclear and atomic collision processes which significantly alter the physical characteristics and biologically important properties of their transported radiation fields. These physical interactions and their effect on the resulting radiation field within matter are described within the context of a recently developed deterministic, coupled neutron-proton space radiation transport computer code (BRYNTRN). Using this computer code, estimates of human exposure in interplanetary space, behind nominal (2 g/cm2) and storm shelter (20 g/cm2) thicknesses of aluminum shielding, are made for the large solar proton event of August 1972. Included in these calculations are estimates of cumulative exposures to the skin, ocular lens, and bone marrow as a function of time during the event. Risk assessment in terms of absorbed dose and dose equivalent is discussed for these organs. Also presented are estimates of organ exposures for hypothetical, worst-case flare scenarios. The rate of dose equivalent accumulation places this situation in an interesting region of dose rate between the very low values of usual concern in terrestrial radiation environments and the high dose rate values prevalent in radiation therapy.     

Geomagnetic transmission disturbances and heavy-ion fluences observed in low Earth orbit during the solar energetic particle events of October 1989.

The large solar energetic particle (SEP) events and simultaneous large geomagnetic disturbances observed during October 1989 posed a significant, rapidly evolving space radiation hazard. Using data from the GOES-7, NOAA-10, IMP-8 and LDEF satellites, we determined the geomagnetic transmission, heavy ion fluences, mean Fe ionic charge state, and effective radiation hazard observed in low Earth orbit (LEO) for these SEPs. We modeled the geomagnetic transmission by tracing particles through the combination of the internal International Geomagnetic Reference Field (IGRF) and the Tsyganenko (1989) magnetospheric field models, extending the modeling to large geomagnetic disturbances. We used our results to assess the radiation hazard such very large SEP events would pose in the anticipated 52 degrees inclination space station orbit.     

December 2006 solar extreme events and their influence on the near-Earth space environment: “Universitetskiy-Tatiana” satellite observations

The Russian microsatellite “Universitetskiy-Tatiana” was launched on Jan. 20, 2005 and was both a scientific and educational mission. Its two main aims were declared as: (1) monitoring of the energetic particles dynamics in the near-Earth space environment after solar events and during quiet times, (2) educational activities based on experimental data obtained from the spacecraft. In this paper observations acquired during Dec. 5–16, 2006, known as “Solar Extreme Events 2006”, were analyzed. The “Universitetskiy-Tatiana” microsatellite orbit permits one to measure both solar energetic particle dynamics, variations of the boundary of solar particle penetration, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. Both relativistic electrons of the Earth’s outer radiation and solar energetic particles are an important source of radiation damage in near-Earth space. Therefore, the presented experimental results demonstrate the successful application of a small educational spacecraft both for scientific and educational programs.     

Inner magnetosphere variations after solar proton events. Observations on Mir space station in 1989-1994 time period.

Measurements on board the Mir space station have been used to study the dose rate and the particle flux distribution in the inner magnetosphere. The measurements have been performed with the Bulgarian-Russian dosimeter-radiometer Liulin. The paper concentrates on the dynamics of the observed "new" and "second" maxima which were created after Solar Proton Events (SPE) in the 1989-1994 time. The "second" belt was first observed after the SPE on October 20, 1989, and the last observation was after the SPE on February 20, 1994. The creation of the "new" belt is a unique phenomena seen in the Liulin data set after the SPE on March 23, 1991 and relates to the magnetic storm on March 24. The new belt fully disappears in the middle of 1993.     

Solar proton events recorded in the stratosphere during cosmic ray balloon observations in 1957–2008

Long-term balloon observations have been performed by the Lebedev Physical Institute since 1957 up to the present time. The observations are taken several times a week at the polar and mid latitudes and allow us to study dynamics of galactic and solar cosmic ray as well as secondary particle fluxes in the atmosphere and in the near-Earth space. Solar energetic particles (120) – mostly protons – (SEP) events with >100 MeV proton intensity above 1 cm⁻² s⁻¹ s⁻¹ were recorded during 1958–2006. Before the advent of the SEP monitoring on spacecraft these results constituted the only homogeneous series of >100 MeV SEP events. The SEP intensities and energy spectra inferred from the Lebedev Physical Institute observations are consistent with the results taken in the adjacent energy intervals by the spacecraft and neutron monitors. Joint consideration of the SEP events series recorded by balloons and by neutron monitors during solar cycles 20–23 makes it possible to restore the probable number of events in solar cycle 19, which was not properly covered by observations. Some correlation was found between duration of SEP event production in a solar cycle and sunspot cycle characteristics.     

Biological dosimetry to determine the UV radiation climate inside the MIR station and its role in vitamin D biosynthesis

The vitamin D synthesis in the human skin, is absolutely dependent on UVB radiation. Natural UVB from sunlight is normally absent in the closed environment of a space station like MIR. Therefore it was necessary to investigate the UV radiation climate inside the station resulting from different lamps as well as from occasional solar irradiation behind a UV-transparent quartz window. Biofilms, biologically weighting and integrating UV dosimeters successfully applied on Earth (e.g. in Antarctica) and in space (D-2, Biopan I) were used to determine the biological effectiveness of the UV radiation climate at different locations in the space station. Biofilms were also used to determine the personal UV dose of an individual cosmonaut. These UV data were correlated with the concentration of vitamin D in the cosmonaut's blood and the dietary vitamin D intake. The results showed that the UV radiation climate inside the Mir station is not sufficient for an adequate supply of vitamin D, which should therefore be secured either by vitamin D supplementat and/or by the regular exposure to special UV lamps like those in sun-beds. The use of natural solar UV radiation through the quartz window for ‘sunbathing’ is dangerous and should be avoided even for short exposure periods.     

Space radiation environment in low earth orbit during influences from solar and geomagnetic events in December 2006

In low earth orbit, the SAA region is the dominant contributor to both proton environment and electron environment from the standpoint of radiation dose for spacecraft lifetime. However, the polar region and the horn region are sometimes strongly disturbed due to large solar and geomagnetic events. During large disturbances, enhancements in proton flux are measured in the polar region, which gives temporary more severe space radiation environment than that given in the SAA region. On the other hand, enhancements in electron flux are measured mainly in the horn region corresponding to the outer radiation belt, which are likely sources of high-energy electrons in the inner radiation belt. These short-term disturbances have another radiation hazard to spacecraft such as single event and electrostatic discharge.     

Solar cosmic rays as a specific source of radiation risk during piloted space flight.

Solar cosmic rays present one of several radiation sources that are unique to space flight. Under ground conditions the exposure to individuals has a controlled form and radiation risk occurs as stochastic radiobiological effects. Existence of solar cosmic rays in space leads to a stochastic mode of radiation environment as a result of which any radiobiological consequences of exposure to solar cosmic rays during the flight will be probabilistic values. In this case, the hazard of deterministic effects should also be expressed in radiation risk values. The main deterministic effect under space conditions is radiation sickness. The best dosimetric functional for its analysis is the blood forming organs dose equivalent but not an effective dose. In addition, the repair processes in red bone marrow affect strongly on the manifestation of this pathology and they must be taken into account for radiation risk assessment. A method for taking into account the mentioned above peculiarities for the solar cosmic rays radiation risk assessment during the interplanetary flights is given in the report. It is shown that radiation risk of deterministic effects defined, as the death probability caused by radiation sickness due to acute solar cosmic rays exposure, can be comparable to risk of stochastic effects. Its value decreases strongly because of the fractional mode of exposure during the orbital movement of the spacecraft. On the contrary, during the interplanetary flight, radiation risk of deterministic effects increases significantly because of the residual component of the blood forming organs dose from previous solar proton events. The noted quality of radiation responses must be taken into account for estimating radiation hazard in space.     

太阳辐射对环火段通信链路的影响分析及参数设计

深空探测的上合阶段(superior solar conjunction,SSC),太阳强辐射成为影响地面站接收噪声温度计算分析的关键性因素之一。针对太阳辐射引起的高传输误码率甚至通信中断问题,以火星探测为例,提出一种定量化计算环火段太阳 地面站 探测器夹角∠SEP的方法,结合角度关系分析了环火段SSC阶段太阳对链路产生影响的原因,重点分析了地面站接收太阳噪声温度与空间链路、空口参数以及天线波束特性之间的关系。研究及仿真试验表明,当天线口径一定时,地面站的接收噪温峰值Tsmax和太阳对地面站的影响时长ti均与通信频率成反比; 在通信频率一定时,Tsmax与天线口径成正比,t_i与天线口径成反比;当天线口径固定为34m时,S频段下的Tsmax高达12830K,是Ka频段下的1.8倍,S频段的ti比Ka频段下的ti表现在∠SEP上延长近0.5°。当通信频率固定为S频段时,70m口径天线与18m口径天线相比,Tsmax高出1920K,但是ti表现在∠SEP上缩短约0.53°。结合太阳辐射对通信链路的影响分析,给出了不同∠SEP下的链路参数设计建议,为火星探测链路中的参数设置提供参考。     

Radiation measurements inside a human phantom aboard the International Space Station using Liulin-5 charged particle telescope

Liulin-5 is a particle telescope developed for the investigation of the radiation environment within the Russian spherical tissue-equivalent phantom on the International Space Station (ISS). Liulin-5 experiment is conducted aboard the Russian segment of ISS since 28 June 2007 as an adherent part of the international project MATROSHKA-R. The main objective of Liulin-5 experiment is to study the depth-dose distribution of the different components of the orbital radiation field in a human phantom. Additional objectives are mapping of the radiation environment in the phantom and its variations with time and orbital parameters (such as solar cycle, solar flare events, inclination and altitude). Liulin-5 is an active instrument, capable to provide real-time radiation data for the particle flux and dose rates, energy deposition and LET spectra. Data are recorded automatically on memory cards, periodically transported to ground by returning vehicles. In this report we present some first results from data analysis including energy deposition spectra, absorbed dose, dose rate and flux distribution measured simultaneously at 3 different depths of phantom’s radial channel and linear energy transfer (LET) spectrum. Data discussed are for the period July 2007–April 2008.