Minimizing space radiation exposure during extra-vehicular activity

Continued assembly of the International Space Station (ISS) requires numerous extra-vehicular activities (EVAs). Prudent radiological safety practices require minimizing additional exposures to crewmen during these periods. The spatial distribution of the “normal” trapped proton and electron radiation sources in low Earth orbit is strongly governed by the geomagnetic field. It is possible to use ISS trajectory information to estimate crew exposures during EVAs and to identify periods that can result in minimal EVA crew exposures through avoidance of these trapped radiation regions. Such exposure minimization planning can also accommodate the unforeseen development of a solar proton event. An EVA exposure estimation tool, EVADOSE, is described and applied to various EVA exposure scenarios. Procedures and parameters that influence EVA exposures are discussed along with techniques to minimize crew exposures.     

Accommodations for earth-viewing payloads on the international space station

The design of the International Space Station (ISS) includes payload locations that are external to the pressurized environment. These external or attached payload accommodation locations will allow direct access to the space environment at the ISS orbit and direct viewing of the earth and space. NASA sponsored payloads will have access to several different types of standard external locations; the S3 Truss Sites, the Columbus External Payload Facility (EPF), and the Japanese Experiment Module Exposed Facility (JEM-EF). As the ISS Program develops, it may also be possible to locate external payloads at the P3 Truss Sites or at non-standard locations similar to the handrail-attached payloads that were flown during the MIR Program. Earth-viewing payloads may also be located within the pressurized volume of the US Lab in the Window Observational Research Facility (WORF). Payload accommodations at each of the locations will be described, as well as transport to and retrieval from the site.     

Method for the prediction of the effective dose equivalent to the crew of the International Space Station

This paper describes a methodology for assessing the pre-mission exposure of space crew aboard the International Space Station (ISS) in terms of an effective dose equivalent. In this approach, the PHITS Monte Carlo code was used to assess the particle transport of galactic cosmic radiation (GCR) and trapped radiation for solar maximum and minimum conditions through an aluminum shield thickness. From these predicted spectra, and using fluence-to-dose conversion factors, a scaling ratio of the effective dose equivalent rate to the ICRU ambient dose equivalent rate at a 10 mm depth was determined. Only contributions from secondary neutrons, protons, and alpha particles were considered in this analysis.     

多舱段载人航天器氧分压控制仿真分析

为确保乘员安全性,载人航天器需通过氧分压控制系统将密封舱内的氧分压控制在指标范围内.提出了一种两舱段载人航天器密封舱氧分压控制系统数学模型,包括密封舱体、乘员、供氧组件、舱间通风(IMV)等多个子模块.通过与相关试验数据进行对比,证明了数学模型的准确性.针对由两个容积为60 m3密封舱组成的组合体,利用该模型分析了乘员驻留位置、舱间通风量、氧分压监测模式对两舱氧分压的影响.结果表明:当舱间通风量为0.5 m3/min 且6人驻留在氧分压非主控舱时,两舱氧分压上限差别达到2.2 kPa.两舱氧分压差别会随着舱间通风量的增加而减小.单舱监测模式和两舱监测模式对两舱氧分压影响并不显著,当舱间通风量超过1.5 m3/min时,两种控制模式的氧分压控制效果趋于一致.      

Effects of exercise equipment on the microgravity environment.

Numerous types of exercise equipment have flown on manned space flights to evaluate and maintain crew members' physical condition while on orbit. Vibrations associated with the use of some exercise equipment cause concern among microgravity scientists who are usually looking for a quiescent environment in which to run their experiments. We discuss the impact of aerobic (bicycle ergometer, treadmill) and non-aerobic (resistance devices) exercise on the microgravity environment of the Space Shuttle Orbiters and the Mir Space Station. In general, characteristic vibration disturbances due to ergometer exercise show the pedalling frequency at 2.5 to 3 Hz and the crew members' body rocking side-to-side at about half the pedalling frequency. For treadmill exercise, the footfall frequency on the treadmill platform can be clearly seen in the 1 to 2 Hz range, along with upper harmonics. The use of resistance exercise devices does not typically cause vibrations. Several vibration isolation systems used on the Orbiters and planned for the International Space Station are introduced. Finally, the responses of specific experiments to exercise vibrations are outlined.     

Virus protein assembly in microgravity.

The coat of polyomavirus is composed of three proteins that can self-assemble to form an icosahedral capsid. VP1 represents 75% of the virus capsid protein and the VP1 capsomere subunits are capable of self assembly to form a capsid-like structure. Ground-based and orbiter studies were conducted with VP1 protein cloned in an expression vector and purified to provide ample quantities for capsomere-capsid assembly. Flight studies were conducted on STS-37 on April 5-9, 1991. Assembly initiated when a VP1 protein solution was interfaced with a Ca+2 buffer solution (pH 5.0). After four days a second alignment terminated the assembly process and allowed for glutaraldehyde fixation. Flight and ground-based samples were analyzed by electron microscopy. Ground-based experiments revealed the assembly of VP1 into capsid-like structures and a heterogenous size array of capsomere subunits. Samples reacted in microgravity, however, showed capsomeres of a homogenous size, but lack of capsid-like assembly.     

Advanced regenerative environmental control and life support systems: Air and water regeneration

Extended manned space missions will require regenerative life support techniques. Past U.S. manned missions used nonregenerative expendables, except for a molecular sieve-based carbon dioxide removal system aboard Skylab. The resupply penalties associated with expendables becomes prohibitive as crew size and mission duration increase. The U.S. Space Station, scheduled to be operational in the 1990's, is based on a crew of four to sixteen and a resupply period of 90 days or greater. It will be the first major spacecraft to employ regenerable techniques for life support. The paper uses the requirements for the Space Station to address these techniques.     

Verification of shielding effect by the water-filled materials for space radiation in the International Space Station using passive dosimeters

The dose reduction effects for space radiation by installation of water shielding material (“protective curtain”) of a stack board consisting of the hygienic wipes and towels have been experimentally evaluated in the International Space Station by using passive dosimeters. The averaged water thickness of the protective curtain was 6.3 g/cm². The passive dosimeters consisted of a combination of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs). Totally 12 passive dosimeter packages were installed in the Russian Service Module during late 2010. Half of the packages were located at the protective curtain surface and the other half were at the crew cabin wall behind or aside the protective curtain. The mean absorbed dose and dose equivalent rates are measured to be 327 μGy/day and 821 μSv/day for the unprotected packages and 224 μGy/day and 575 μSv/day for the protected packages, respectively. The observed dose reduction rate with protective curtain was found to be 37 ± 7% in dose equivalent, which was consistent with the calculation in the spherical water phantom by PHITS. The contributions due to low and high LET particles were found to be comparable in observed dose reduction rate. The protective curtain would be effective shielding material for not only trapped particles (several 10 MeV) but also for low energy galactic cosmic rays (several 100 MeV/n). The properly utilized protective curtain will effectively reduce the radiation dose for crew living in space station and prolong long-term mission in the future.     

Recent Development in the Space Utility System of China's Manned Space Flight Program

This paper briefly introduces the history of China's Manned Space Flight Program and concludes the experiments done since 2008, namely, a small satellite and a material science experiment. An outlook of future Chinese Space Station is also described at the end.      

飞行模拟技术在红外/微波复合导引头测试中的研究与应用

飞行模拟技术在导引头研制的各个阶段都发挥着重要的作用,以微波暗室环境下复合导引头飞行模拟自动化测试系统为工程背景,其包含主控系统、三轴转台、二维目标三大分系统,是一套集机、光、电为一体的大型综合性测试系统。详述了测试系统的软硬件设计原理,通过五轴系统设计、转台与目标的分体式同步联动、二维目标模拟装置的精准平稳传动、陀螺指向测试的转台偏角修正算法几大关键创新型技术,建立起了一套飞行模拟自动化测试系统,解决了目标飞行轨迹模拟、导引头调试测试的难题,实现了红外/微波复合导引头动态特性的自动化测试。     

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.     

太阳活动区R9077引起的强烈吸收事件

利用南极中山站的观测数据分析了太阳活动区R9077所引起的强烈吸收事件，其中2000年7月14日的太阳质子事件引起了持续3天多强烈的极盖吸收，同时，激烈的太阳活动使磁层处于极度扰动状态，磁层高能粒子沉降使许多持续时间较短的吸收峰叠加在极盖吸收背景之上，最突出的是7月1日的吸收增强事件，其最大值达26dB。这是自1997年2月中山站安装成像式宇宙噪声接收机以来观测到的最强的吸收，另一个较突出的吸收峰发生在14日1753UT前后，本文还讨论了产生这些吸收的原由。     

Simulations of absorbed dose on the phantom surface of MATROSHKA-R experiment at the ISS

The health risks associated with exposure to various components of space radiation are of great concern when planning manned long-term interplanetary missions, such as future missions to Mars. Since it is not possible to measure the radiation environment inside of human organs in deep space, simulations based on radiation transport/interaction codes coupled to phantoms of tissue equivalent materials are used. However, the calculated results depend on the models used in the codes, and it is therefore necessary to verify their validity by comparison with measured data. The goal of this paper is to compare absorbed doses obtained in the MATROSHKA-R experiment performed at the International Space Station (ISS) with simulations performed with the three-dimensional Monte Carlo Particle and Heavy-Ion Transport code System (PHITS). The absorbed dose was measured using passive detectors (packages of thermoluminescent and plastic nuclear track detectors) placed on the surface of the spherical tissue equivalent phantom MATROSHKA-R, which was exposed aboard the ISS in the Service Zvezda Module from December 2005 to September 2006. The data calculated by PHITS assuming an ISS shielding of 3 g/cm² and 5 g/cm² aluminum mass thickness were in good agreement with the measurements. Using a simplified geometrical model of the ISS, the influence of variations in altitude and wall mass thickness of the ISS on the calculated absorbed dose was estimated. The uncertainties of the calculated data are also discussed; the relative expanded uncertainty of absorbed dose in phantom was estimated to be 44% at a 95% confidence level.     

PHITS simulations of the Protective curtain experiment onboard the Service module of ISS: Comparison with absorbed doses measured with TLDs

“Protective curtain” was the physical experiment onboard the International Space Station (ISS) aimed on radiation measurement of the dose – reducing effect of the additional shielding made of hygienic water-soaked wipes and towels placed on the wall in the crew cabin of the Service module Zvezda. The measurements were performed with 12 detector packages composed of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs) placed at the Protective curtain, so that they created pairs of shielded and unshielded detectors.     

Micro-meteoroids and space debris impact risk assessment for the ConeXpress satellite using ESABASE2/Debris

Micro-meteoroid and space debris impact risk assessments are performed to investigate the risk from hypervelocity impacts to sensitive spacecraft sub-systems. For these analyses, ESA’s impact risk assessment tool ESABASE2/Debris is used. This software tool combines micro-particle environment models, damage equations for different shielding designs and satellite geometry models to perform a detailed 3D micro-particle impact risk assessment. This paper concentrates on the impact risk for exposed pressurized tanks. Pressure vessels are especially susceptible to hypervelocity impacts when no protection is available from the satellite itself. Even small particles in the mm size range can lead to a fatal burst or rupture of a tank when impacting with a typical collision velocity of 10–20 km/s. For any space mission it has to be assured that the impact risk is properly considered and kept within acceptable limits. The ConeXpress satellite mission is analysed as example. ConeXpress is a planned service spacecraft, intended to extend the lifetime of telecommunication spacecraft in the geostationary orbit. The unprotected tanks of ConeXpress are identified as having a high failure risk from hypervelocity impacts, mainly caused by micro-meteoroids. Options are studied to enhance the impact protection. It is demonstrated that even a thin additional protective layer spaced several cm from the tank would act as part of a double wall (Whipple) shield and greatly reduce the impact risk. In case of ConeXpress with 12 years mission duration the risk of impact related failure of a tank can be reduced from almost 39% for an unprotected tank facing in flight direction to below 0.1% for a tank protected by a properly designed Whipple shield.     

Automated guidance algorithms for a space station-based crew escape vehicle.

An escape vehicle was designed to provide an emergency evacuation for crew members living on a space station. For maximum escape capability, the escape vehicle needs to have the ability to safely evacuate a station in a contingency scenario such as an uncontrolled (e.g., tumbling) station. This emergency escape sequence will typically be divided into three events: The first separation event (SEP1), the navigation reconstruction event, and the second separation event (SEP2). SEP1 is responsible for taking the spacecraft from its docking port to a distance greater than the maximum radius of the rotating station. The navigation reconstruction event takes place prior to the SEP2 event and establishes the orbital state to within the tolerance limits necessary for SEP2. The SEP2 event calculates and performs an avoidance burn to prevent station recontact during the next several orbits. This paper presents the tools and results for the whole separation sequence with an emphasis on the two separation events. The first challenge includes collision avoidance during the escape sequence while the station is in an uncontrolled rotational state, with rotation rates of up to 2 degrees per second. The task of avoiding a collision may require the use of the Vehicle's de-orbit propulsion system for maximum thrust and minimum dwell time within the vicinity of the station vicinity. The thrust of the propulsion system is in a single direction, and can be controlled only by the attitude of the spacecraft. Escape algorithms based on a look-up table or analytical guidance can be implemented since the rotation rate and the angular momentum vector can be sensed onboard and a-priori knowledge of the position and relative orientation are available. In addition, crew intervention has been provided for in the event of unforeseen obstacles in the escape path. The purpose of the SEP2 burn is to avoid re-contact with the station over an extended period of time. Performing this maneuver requires knowledge of the orbital state, which is obtained during the navigation state reconstruction event. Since the direction of the delta-v of the SEP1 maneuver is a random variable with respect to the Local Vertical Local Horizontal (LVLH) coordinate system, calculating the required SEP2 burn is a challenge. This problem was solved using elements of neural network theory for model-free function approximation and decision making.     

“风云一号（B）”卫星探测到的太阳质子事件

我国“风云一号(B)”气象卫星于1990年9月3日发射入轨,该星载有粒子成分监测器,用来探测空间粒子辐射环境,其中包括测量太阳耀斑时产生的太阳质子事件及其重粒子丰度;银河宇宙线异常成分与强度;内辐射带磁异常区的粒子通量及重粒子成分,“风云一号(B)”卫星运行半年来,我们已获取了上述有关的粒子辐射资料,在卫星上获得这些资料在我国尚属首次,本文主要分析观测到的太阳质子事件。     

嫦娥一号卫星的地月转移变轨控制

文章阐述了嫦娥一号卫星地月转移阶段(从星箭分离到进入使命轨道)的高可靠、高精度自主变轨控制方案,介绍了飞行轨道、轨控策略及控制参数优化、星上自主变轨控制的系统设计和相关参数的地面标定等,给出了在轨飞行试验的验证结果。     

Possible mechanism of microgravity impact on Carausius morosus ontogenesis.

Experiments aboard "Spacelab-D1" and "Cosmos-1887" revealed an adverse effect of space flight on Carausius morosus embryos. The main influencing factor for stick insect eggs turned out to be microgravity, while the contribution of HZE particles of cosmic radiation was relatively low. Flight experiments indicated an increased vulnerability of stick insect eggs to microgravity at intermediate stages of development, that could support the "convection" hypothesis.     

Numeric simulations of in situ observations of interacting ejecta near 1 AU

We use a simple numerical model (González-Esparza, J.A., Santillán, A., Ferrer, J. A numerical study of the interaction between two ejecta in the interplanetary medium: one and two dimensional hydrodynamic simulations, Ann. Geophys. 22, 3741–3749, 2004) to study the evolution of three events in the solar wind reported by Wang et al. (Wang, Y.M., Ye, P.Z., Wang, S. Multiple magnetic clouds: several examples during March–April 2001. J. Geophys. Res. 108, 1370, 2003, doi:10.1029/2003JA009850), where two interacting ejecta detected in situ by ACE near 1 AU were related to CMEs observed previously by SOHO-LASCO. The study is based on a 1-D hydrodynamic model using the ZEUS code (Stone, J.M., Norman, M. ZEUS 2-D: A radiation magnetohydrodynamics code for astrophysical flows in two dimensions, I, the hydrodynamics algorithms and tests, Astrophys. J. 80, 753, 1992). Although this model cannot address either the magnetic field dynamics or the complex geometrical effects intrinsic in the three-dimensional nature of the phenomena, it illuminates the transferring of momentum and evolution of interacting large-scale solar wind disturbances in those cases where there is no merging (magnetic reconnection) between the two ejecta. This model can reproduce, in some cases, characteristics of the events such as transit times and flow signatures as inferred from the two-point measurements from spacecraft.