Space Shuttle drops down the SAA doses on ISS

Long-term analysis of data from two radiation detection instruments on the International Space Station (ISS) shows that the docking of the Space Shuttle drops down the measured dose rates in the region of the South Atlantic Anomaly (SAA) by a factor of 1.5–3. Measurements either by the R3DE detector, which is outside the ISS at the EuTEF facility on the Columbus module behind a shielding of less than 0.45 g cm⁻², and by the three detectors of the Liulin-5 particle telescope, which is inside the Russian PEARS module in the spherical tissue equivalent phantom behind much heavier shielding demonstrate that effect. Simultaneously the estimated averaged incident energies of the incoming protons rise up from about 30 to 45 MeV. The effect is explained by the additional shielding against the SAA 30–150 MeV protons, provided by the 78 tons Shuttle to the instruments inside and outside of the ISS. An additional reason is the ISS attitude change (performed for the Shuttle docking) leading to decreasing of dose rates in two of Liulin-5 detectors because of the East–West proton fluxes asymmetry in SAA. The Galactic Cosmic Rays dose rates are practically not affected.     

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.     

质子辐射带辐射中心区域模型

利用AP-8和CRRESPRO质子辐射带模式数据库, 比较了二者在磁赤道面上计算结果 的差异并给出其差异原因. 利用AP-8模式数据库数据, 建立起质子辐射带函数形式的辐射中心区域模式, 包括各能道全向微分通量峰值所对应的L值(L_c) 随能量E的变化模式以及各能道全向微分通量峰值J_max随能量E的变化模式. 利用RBSP A卫星REPT望远镜在磁赤道面上的高能质子观测数据, 分别与 AP-8模式、CRRESPRO模式及本文所得辐射中心区域模式计算结果进行比较, 发现在78.9, 102.6和208MeV三个能道上, RBSP A卫星观测所得各能道全向微分 通量明显偏大, 而L_c与AP-8或本文辐射中心模式所得结果基本一致; RBSP A卫星也观测到CRRESPRO Quiet模式所得的隐性第二质子辐射带结构.      

FEM code simulation of the magnetospheric proton fluxes

We report a study of the numeric solution to the diffusive transport equation for energetic protons magnetically trapped in the Earth's equatorial magnetosphere. The analysis takes into account the pertinent physical processes in this region, including deceleration of protons by Coulomb collisional interactions with free and bound electrons, the charge exchange process, cosmic ray albedo neutron decay source, and electric and magnetic radial diffusion. These results were obtained using the Finite Element Method with magnetic moment and geomagnetic L-shell as free variables. Steady state boundary conditions were imposed at L=1 as zero distribution function and at L=7 with proton distribution function extracted from ATS 6 satellite observations. The FEM-code yields unidirectional proton flux in the energy range of 0.1–1000 MeV at the equatorial top of the geomagnetic lines, and the results are found to be in satisfactorily agreement with the empirical NASA AP-8 model proton flux within the energy range of 0.5–100 MeV. Below 500 keV, the empirical AP-8 model proton fluxes are several orders of magnitude greater than those computed with the FEM-code at L<3. This discrepancy is difficult to explain by uncertainties of boundary spectrum parameters or transport coefficients.     

太阳周期活动对低高度内辐射带高能质子的影响

利用NOAA-15卫星1998年到2011年近13年的高能质子全向通量观测资料, 分析了一个太阳活动周内, 低高度内辐射带高能质子通量的分布变化特性及其物理原因, 比较了观测结果与AP8模型的不同. 研究表明, 低高度内辐射带高能质子通量与太阳活动水平的反相关关系与磁壳参数L值及磁场B值有关; L值越低, B值越大的空间点, 其高能质子通量与太阳活动水平的反向相关性越明显. 高能质子通量随太阳活动水平的变化存在明显滞后现象, L值越高、 B值越小的空间点, 滞后现象就越明显, 滞后严重时可以达到一年左右的时间; 这种滞后现象反映出低高度内辐射带高能质子的源与损失达到平衡是一个中长期过程. 通过与AP8模型计算结果的比较分析可以看出, 利用AP8模型时, 仅考虑地磁场长期变化对质子通量的影响可能会夸大低高度内辐射带局部高能质子通量的增强.      

Inner radiation belt source of helium and heavy hydrogen isotopes

Nuclear interactions between inner zone protons and atoms in the upper atmosphere provide the main source of energetic H and He isotopes nuclei in the radiation belt. This paper reports on the specified calculations of these isotope intensities using various inner zone proton intensity models (AP-8 and SAMPEX/PET PSB97), the atmosphere drift-averaged composition and density model MSIS-90, and cross-sections of the interaction processes from the GNASH nuclear model code. To calculate drift-averaged densities and energy losses of secondaries, the particles were tracked in the geomagnetic field (modelled through IGRF-95) by integrating numerically the equation of the motion. The calculations take into account the kinematics of nuclear interactions along the whole trajectory of trapped proton. The comparison with new data obtained from the experiments on board RESURS-04 and MITA satellites and with data from SAMPEX and CRRES satellites taken during different phases of solar activity shows that the upper atmosphere is a sufficient source for inner zone helium and heavy hydrogen isotopes. The calculation results are energy spectra and angular distributions of light nuclear isotopes in the inner radiation belt that may be used to develop helium inner radiation belt model and to evaluate their contribution to SEU (single event upset) rates.     

低高度空间高能质子通量分布计算

介绍了AP-8模式、CRRESPRO模式和PSB97模式,并用这3种模式分别计算低高度空间300—1100km范围内的高能质子通量分布,由IDL软件绘出通量等值线图．AP-8模式通量主要受银河宇宙线调制,即受太阳活动直接影响,与太阳活动高年相比,太阳活动低年的质子通量较大;CRRESPRO模式中,因活动期和平静期的数据采集时间前后相差很短,从而使同一高度上两种环境条件下的通量分布相似．模式之间的比较结果表明,AP-8模式通量较小,CRRESFRO模式通量较大,PSB97模式通量介于二者之间,并与实测通量接近．PSB97是为低高度(1000km以下)定制的模式,在低高度上优于AP-8模式和CRRESPRO模式,能较好地计算当前条件下的低高度高能质子通量．     

辐射带AP9模式在南大西洋异常区的系统性量化评估

针对目前辐射带AP9模式量化评估不够系统的问题，基于F_10.7指数确定高、中、低太阳活动水平，以三种太阳活动水平条件下NOAA-15观测的140~500MeV的全向质子通量为参考数据，以南大西洋异常区为对比区域，定义边界吻合度和大小量级差为评估指标，将辐射带AP9模式分别与AP8模式和参考数据进行对比，对AP9模式进行系统性量化评估.结果表明，AP8和AP9模式均能重构出南大西洋异常区，但AP8模式重构的南大西洋异常区轮廓与观测结果更为吻合.平均而言，AP8和AP9模拟结果均比观测值高，AP8比AP9更接近观测值.太阳活动水平越低，AP9与观测之间的差距越小.      

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.     

X-ray astronomy from the space shuttle

A wide variety of new X-ray instrumentation is being proposed to attack an even wider variety of astrophysical problems. It includes general-purpose instruments which, with further development and testing, may someday be part of the complement of an orbiting “observatory” facility, such as AXAF. Other instruments promise significant and often necessary advantages for a narrower range of problems. The testing and development of all of these ideas, and in particular finding an efficient way to employ the latter class to make the observations for which they are intended, pose dilemmas for which the Space Shuttle potentially offers solutions. A discussion of possible modes for using the Shuttle and a brief sampling of new instrumentation ideas are presented.     

Measurements of trapped protons and cosmic rays from recent Shuttle flights.

We have flown two new charged particle detectors in five recent Shuttle flights. In this paper we report on the dose rate, equivalent dose rate, and radiation quality factor for trapped protons and cosmic radiation separately. A comparison of the integral linear energy transfer (LET) spectra with recent transport code calculations show significant disagreement. Using the calculated dose rate from the omni-directional AP8MAX model with IGRF reference magnetic field epoch 1970, and observed dose rate as a function of (averaged over all geographic latitude) and longitude, we have determined the westward drift of the South Atlantic anomaly. We have also studied the east-west effect, and observed a 'second' radiation belt. A comparison of the galactic cosmic radiation lineal energy transfer spectra with model calculations shows disagreement comparable to those of the trapped protons.     

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.     

Radiation measurements on the flight of IML-2.

The second flight of the International Microgravity Laboratory (IML-2) on Space Shuttle flight STS-65 provided a unique opportunity for the intercomparison of a wide variety of radiation measurement techniques. Although this was not a coordinated or planned campaign, by sheer chance, a number of space radiation experiments from several countries were flown on this mission. There were active radiation measuring instruments from Japan and US, and passive detectors from US, Russia, Japan, and Germany. These detectors were distributed throughout the Space Shuttle volume: payload bay, middeck, flight deck, and Spacelab. STS-65 was launched on July 8, 1994, in a 28.45 degrees x 306 km orbit for a duration of 14 d 17 hr and 55 min. The crew doses varied from 0.935 mGy to 1.235 mGy. A factor of two variation was observed between various passive detectors mounted inside the habitable Shuttle volume. There is reasonable agreement between the galactic cosmic ray dose, dose equivalent and LET spectra measured by the tissue equivalent proportional counter flown in the payload bay with model calculations. There are significant differences in the measurements of LET spectra measured by different groups. The neutron spectrum in the 1-20 MeV region was measured. Using fluence-dose conversion factors, the neutron dose and dose equivalent rates were 11 +/- 2.7 microGy/day and 95 +/- 23.5 microSv/day respectively. The average east-west asymmetry of trapped proton (>3OMeV) and (>60 MeV) dose rate was 3.3 and 1.9 respectively.     

REM measurements aboard Mir during 1995

Measurements of the South Atlantic Anomaly (SAA) made with the Radiation Environment Monitor (REM) aboard Mir from November 1994 to February 1996 are presented. During this period an increase of the SAA radiation by ≈25% is observed, which coincides with a lowering of the radio solar flux. Radio solar flux is one of the parameters controlling the earth's atmospheric distribution and with it the absorption of inner radiation belt protons forming the SAA. Due to the altitude gradient of the atmospheric density, the proton fluxes in the SAA are anisotropic (loss cone, east-west effect). The measured distribution can be accounted for by basic models.     

漂移壳追踪方法与内辐射带的长期变化

地磁场的长期变化发迹辐射带结构,如何在当前年代下恰当地使用ＡＥ－８／ＡＰ－８模型,目前国内外对此问题存在着很大的争议。我们在物理分析的基础上给出了当前年代下使用辐射带模型ＡＰ－８的漂移壳追踪方法ＤＳＴＭ（Ｄｒｉｆｔ Ｓｈｅｌｌ Ｔｒａｃｉｎｇ Ｍｅｔｈｏｄ）。计算结果表明地磁场的长期变化对内辐射带的通量分布有着显著的影响。３０－４０年来,南大西洋通量异常区中心向丁和向北发生偏移,高粒子辐射区域的范     

BBXRT observations of supernova remnants

The Broad Band X-Ray Telescope (BBXRT) was designed to perform sensitive, moderate resolution spectroscopy of cosmic X-ray sources in the 0.3–10 keV band from the Space Shuttle. During its nine-day flight in December, 1990, the BBXRT observed a variety of supernova remnants and related objects. We present results from some of these observations, emphasizing the ability of the BBXRT to perform spatially-resolved spectroscopy. The improved spectral resolution and efficiency over previous instruments makes possible measurements of previously undetectable lines, and the broad bandpass allows simultaneous measurements of lines from oxygen through iron.     

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.     

Trapped particle energy spectrum in shuttle middeck

We describe the differential energy spectrum of trapped particles measured by a solid-state charged particle telescope in the mid-deck of the Space Shuttle during the period of solar maximum. The telescope was flown in two high altitude flights at 28.5° and 57° inclination. Assuming, as is normally done, that the variations of Shuttle orientation during the missions lead to average isotropic incident spectra, the observed spectrum disagrees significantly from AP8 model calculations. This indicates the need to take into consideration the variations of solid-angle direction relative to the magnetic field. The measurements show that there is a very significant flux of secondary light ions. The energy spectra of these ions does not agree with the production spectrum from radiation transport calculations based on omni-directional AP8 Max model as an input energy spectrum.

We also describe measurements of linear energy transfer spectra using a tissue equivalent proportional counter (TEPC) flown both in the mid-deck and the payload bay of the Space Shuttle. Comparisons are made between linear energy transfer spectral measurements AP8 model-based radiation transport predictions, and thermoluminescent dosimeter (TLD) measurements. The absorbed dose-rate measurements using TLD's are roughly 25% lower than the TEPC-measured dose rate measurements.     

On the spatial extent of the proton radiation belt from solar cell output variation of the Akebono satellite

Output current of silicon solar cells of Akebono satellite orbiting in the inner magnetosphere decreased from 13 A in 1989 to about 7 A in 2009, due to accumulated damage by energetic particles. A fair correlation between the monthly decrease rate of solar cell output current and trapped proton flux was found between 1989 and 1992, indicating that trapped energetic protons are responsible for the solar cell degradation. Simple variation from month to month was dominated by a fluctuation with one-year period and the correlation was not discernible after 1993. On the other hand, during orbiting the earth, another kind of decrease of output current emerged at low altitude above the sub-solar point, i.e., in the midst of sunlit condition. The decrease was larger in later years. The fact indicates more prominent temperature effect in the later years because of progress of the degradation. By removing data affected by the orbit condition above, variation from the same month in the previous year shows a clear oscillation due to orbit precession correlated with trapped energetic proton flux up to 1996. The amplitude of the annual variation oscillation tends to be larger than that expected from a degradation model based on energetic proton distribution of the NASA’s AP8 model. The larger oscillation amplitude suggests that the proton radiation belt was more sharply localized than given by the AP8 model throughout the early half of 1990s.     

Dynamics of the low altitude secondary proton radiation belt

At the interface between the upper atmosphere and the radiation belt region, there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and the main radiation belt and then re-ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64 – 35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the three year period from 21 February 1984 to 26 March 1987 using data obtained with the HEP experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of −1.2 cm⁻² s⁻¹ sr⁻¹ was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically two orders of magnitude). These flux decreases were also long in duration (lasting up to three months). We also registered abrupt flux increases where the magnitude of the proton flux enhancements could reach three orders of magnitude with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.