火星沙尘环境光学图像增强方法

针对火星探测器着陆时沙尘天气对机器视觉的影响,提出一种去除沙尘天气对光学成像影响的方法,为视觉系统提供清晰输入图像。首先对受沙尘天气影响的图像建立模型,然后求取模型中大气光值与透射系数值。对于大气光值的计算采用基于四叉树细分的方法,在最小值图像上搜寻指定阈值面积中灰度均值最大的区域,在初始图像中相同区域计算各通道均值,作为大气光值。在此基础上计算透射系数,完成清晰图像的恢复。通过对受沙尘影响图像测试表明,该方法能够将受沙尘影响的图像恢复成清晰的图像。即使在复杂的环境中,该方法对光照变化、沙尘强度变化和场景变化等仍具有较好的效果。与其他方法相比,本文方法在去除沙尘对光学图像影响方面效果较好,在恢复图像评价指标等方面优于其他方法,能够进一步提高图像清晰度,为光学图像的后期处理提供更丰富信息。      

Electric discharge in the Martian atmosphere,Paschen curves and implications for future missions

Electric discharge between two electrically charged surfaces occurs at a well-defined, gas-dependent combination of atmospheric pressure and the distance between those two surfaces, as described by Paschen’s law. The understanding of when the discharge will occur in the conditions present on Mars is essential for designing space-flight hardware that will operate on the Martian surface as well as understanding electrical discharge processes occurring in the Martian atmosphere. Here, we present experimentally measured Paschen curves for a gas mixture representative of the Martian atmosphere and compare our results to breakdown voltages of carbon dioxide, nitrogen, and helium as measured with our system and from the literature. We will discuss possible implications for instrument development as well as implications for processes in the Martian atmosphere. The DC voltage at which electric discharge occurred between two stainless steel spheres was measured at pressures from 10⁻² to 100 torr in all gases. We measured a minimum voltage for discharge in the Mars ambient atmosphere of 410 ± 10 V at 0.3 torr cm. As an application, the breakdown properties of space-qualified, electrical wires to be used in the Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) were studied.     

A space radiation shielding model of the Martian radiation environment experiment (MARIE)

The 2001 Mars Odyssey spacecraft was launched towards Mars on April 7, 2001. Onboard the spacecraft is the Martian radiation environment experiment (MARIE), which is designed to measure the background radiation environment due to galactic cosmic rays (GCR) and solar protons in the 20–500 MeV/n energy range. We present an approach for developing a space radiation-shielding model of the spacecraft that includes the MARIE instrument in the current mapping phase orientation. A discussion is presented describing the development and methodology used to construct the shielding model. For a given GCR model environment, using the current MARIE shielding model and the high-energy particle transport codes, dose rate values are compared with MARIE measurements during the early mapping phase in Mars orbit. The results show good agreement between the model calculations and the MARIE measurements as presented for the March 2002 dataset.     

Thin film surface treatments for lowering dust adhesion on Mars Rover calibration targets

The current generation of calibration targets on Mars Rover serve as a color and radiometric reference for the panoramic camera. They consist of a transparent silicon-based polymer tinted with either color or grey-scale pigments and cast with a microscopically rough Lambertian surface for a diffuse reflectance pattern. This material has successfully withstood the harsh conditions existent on Mars. However, the inherent roughness of the Lambertian surface (relative to the particle size of the Martian airborne dust) and the tackiness of the polymer in the calibration targets has led to a serious dust accumulation problem. In this work, non-invasive thin film technology was successfully implemented in the design of future generation calibration targets leading to significant reduction of dust adhesion and capture. The new design consists of a μm-thick interfacial layer capped with a nm-thick optically transparent layer of pure metal. The combination of these two additional layers is effective in burying the relatively rough Lambertian surface while maintaining diffuse properties of the samples which is central to the correct operation as calibration targets. A set of these targets are scheduled for flight on the Mars Phoenix mission.     

火星信道衰落特性对通信链路预算的影响

对火星星体段的信道衰落特性进行研究.通过对近火段自然环境因素的分析,提取影响火星通信性能的因素,重点分析火星的大气、云雾、沙尘对通信信道的衰落作用机理;并以NASA实际火星探测任务为例,针对以上衰落因素对UHF,S,X和Ka频段下的通信链路影响情况进行仿真;结合实际探测数据对地球通信链路预算模型进行修正,提出一种适用于火星通信链路预算的模型;明确火星大气衰落、云雾衰落、沙尘衰落的取值范围.研究结果可作为火星及其他深空探测任务的通信系统设计与链路复核复算的参考.     

Effects of lunar and mars dust simulants on HaCaT keratinocytes and CHO-K1 fibroblasts

Exposure to lunar dust during Apollo missions resulted in occasional reports of ocular, respiratory and dermal irritations which showed that lunar dust has a risk potential for human health. This is caused by its high reactivity as well as its small size, leading to a wide distribution also inside habitats. Hence, detailed information regarding effects of extraterrestrial lunar dusts on human health is required to best support future missions to moon, mars or other destinations. In this study, we used several methods to assess the specific effects of extraterrestrial dusts onto mammalian skin by exposing HaCaT keratinocytes and CHO-K1 fibroblasts to dusts simulating lunar or mars soils. These particular cell types were chosen because the skin protects the human body from potentially harmful substances and because a well orchestrated program ensures proper wound healing. Keratinocytes and fibroblasts were exposed to the dusts for different durations of time and their effects on morphology and viability of the cells were determined. Cytotoxicity was measured using the MTT assay and by monitoring culture impedance, while phalloidin staining of the actin cytoskeleton was performed to address structural integrity of the cells which was also investigated by propidium iodide intake. It was found that the effects of the two types of dust simulants on the different features of both cell lines varied to a considerable extent. Moreover, proliferation of HaCaT keratinocytes, as analyzed by Ki67 labeling, was suppressed in sub-confluent cultures exposed to lunar dust simulant. Furthermore, experimental evidence is provided for a delay in regeneration of keratinocyte monolayers from scratch-wounding when exposed to lunar dust simulant. The obtained results will facilitate further investigations of dust exposure during wound healing and will ease risk assessment studies e.g., for lunar lander approaches. The investigations will help to determine safety measures to be taken during extraterrestrial expeditions in order to minimize risks to human health associated with exposure of human skin to dust contaminants.     

Search for organic molecules at the Mars surface: The “Martian Organic Material Irradiation and Evolution” (MOMIE) project

The life on Mars remains an open question because of the lack of proof of its past emergence and its current presence. The only indices of a potential Martian life were provided by the Viking Landers, and the study of the Martian meteorite ALH84001 discovered in the Antarctic. In the two case, the results of experiments could be explained either by the presence of life forms or by abiotic processes. The recent data of Mars Express orbiter and Mars Exploration Rovers show different proofs of a past environment favourable for life. Among the targets we seek, the organic molecules are primordial because they are necessary to the origin of life. A key question is to know if they are present, in which concentration and under which form. Within the framework of a search for organic, we are developing an experimental setup simulating as close as possible the environmental conditions of Mars surface in order to determine how organic species evolve. We present here the first step of the development of this experiment which focuses on the study of the impact of the solar UV radiations reaching the Mars surface on glycine. First results show that glycine does not resist if directly exposed to UV radiations.     

基于工程约束的火星着陆区选择

火星着陆区选择是火星着陆及巡视任务的重要工作之一,着陆区选择需要兼顾科学目标和工程约束,考虑高风险的任务特点,火星着陆任务的工程约束更为重要。工程约束涉及着陆区表面特征、任务轨道、大气等。表面特征包括地理高程、斜坡及地形起伏、岩石分布、尘土厚度、光照、热约束情况。这些因素将影响探测器进入、下降和着陆(EDL)过程的安全性和火星车移动能力。首先针对这些工程约束进行了排序与筛选;然后建立了基于模糊算法的分析模型,通过模糊推理得到各着陆区域的评价指标,从而进行着陆区选择;最后基于ExoMars2020任务的备选着陆区进行了方法验证。     

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.     

Cancer risk above 1 Gy and the impact for space radiation protection

Analyses of the epidemiological data on the Japanese A-bomb survivors, who were exposed to γ-rays and neutrons, provide most current information on the dose–response of radiation-induced cancer. Since the dose span of main interest is usually between 0 and 1 Gy, for radiation protection purposes, the analysis of the A-bomb survivors is often focused on this range. However, estimates of cancer risk for doses larger than 1 Gy are becoming more important for long-term manned space missions. Therefore in this work, emphasis is placed on doses larger than 1 Gy with respect to radiation-induced solid cancer and leukemia mortality. The present analysis of the A-bomb survivors data was extended by including two extra high-dose categories and applying organ-averaged dose instead of the colon-weighted dose. In addition, since there are some recent indications for a high neutron dose contribution, the data were fitted separately for three different values for the relative biological effectiveness (RBE) of the neutrons (10, 35 and 100) and a variable RBE as a function of dose. The data were fitted using a linear and a linear-exponential dose–response relationship using a dose and dose-rate effectiveness factor (DDREF) of both one and two. The work presented here implies that the use of organ-averaged dose, a dose-dependent neutron RBE and the bending-over of the dose–response relationship for radiation-induced cancer could result in a reduction of radiation risk by around 50% above 1 Gy. This could impact radiation risk estimates for space crews on long-term mission above 500 days who might be exposed to doses above 1 Gy. The consequence of using a DDREF of one instead of two increases cancer risk by about 40% and would therefore balance the risk decrease described above.     

Numerical simulations of the regional characteristics of dust transport on Mars

Using a Martian general circulation model (GCM), regions favorable for expansion of dust storms on Mars are identified. Dust transport simulations for the northern fall provide global maps of dust expansibility. These global maps show that dust injected from certain areas in the northern mid-latitudes tends to spread widely within a few days. The high expansibility of dust in such areas results from thermal tides, baroclinic waves, and quasi-stationary disturbances. Dust injected into the vast regions around Tharsis and the Sirenum–Aonia regions also tends to spread extensively. However, dust expansion around these two regions largely depends on the local time of dust injection. On the other hand, dust injected at high latitudes in either hemisphere does not spread extensively. Such global maps indicating regions favorable for dust storm expansion are a clue to understanding the expansion processes and climatology of great dust storms on Mars.     

Moon surface radiation environment analysis for February 1956 solar event conditions

The radiation environment on the surface of the Moon presents a new source of particles resulting from the interaction of incoming solar protons and galactic cosmic rays with the lunar regolith. Here we present a study of the fluence profile of primary and secondary particles on the top 1 m layer of lunar regolith for the spectrum of one of the hardest spectrum solar event, that of February 1956. Different regolith compositions and their influence in proton and neutron production and backscattering is considered, as well as the nature of the backscattered radiation. Simple geometry Monte Carlo simulations have been used also for calculating regolith shielding properties, and it is shown that a layer of at least 50 cm regolith is needed for significantly reducing the dose levels received by astronauts in a hypothetical lunar habitat.     

Experimental investigation on silica dust lofting due to charging within micro-cavities and surface electric field in the vacuum chamber

The charged dust particles can be mobilized electrostatically by the repulsion between the adjacent grains and the surface electric field due to the incoming electron current and the charge accumulation within the micro-cavities. In this study, the experimental results of the initial vertical launching velocities and the maximum dust heights are compared with the estimated values for the lofted spherical dust grains by the patch surface charging equations. Silica particles with the sizes between <6 and 45?µm in radius are loaded on a graphite plate, and they are exposed to the electron beam with 450?eV energy under 4?×?10^?3?Pa vacuum chamber pressure. During the first set of the experiments, the dust samples are tested without an initial compression process and an additional horizontal electric field. Second, the dust samples are compressed by two different weights in order to increase the packing density under approximately 780.7?Pa and 3780?Pa. Finally, the dust grains are placed between the two parallel aluminum plates to apply approximately 2000?V/m and 4800?V/m horizontal electric field. A high-speed camera is used to record the transportation of the dust grains together with a microscopic telescope, and the results point out that the patch surface dust-charging model estimations are in agreement with the first experiments. On the other hand, the dust particles from the compressed samples are lofted with higher velocities than the estimations, and the number of the dust lofting observations decreases significantly, which demonstrates the importance of the micro-cavities and the increased charging requirement to overcome the contact forces. When the horizontal electric field is present, the initial vertical launching velocities are measured to be lower than the other experiments, which can be attributed to the decreased charging requirement for the dust lofting as a result of inter-particle collisions and rolling motion. According to the experimental results, the electrostatic dust transportation can be controlled not only by the ambient plasma and the solar irradiation on the airless planetary bodies, but also by the surface properties such as the contact surfaces between the dust grains, the number of the micro-cavities related to the packing density, and the presence of the horizontal electric field contributing to the external forces by other particle motions.     

火星表面热环境对航天器热控影响分析

火星大气对太阳辐射产生吸收和散射作用,同时还将与火星表面航天器发生对流换热.热设计时难以直接评估对流、辐射和导热三种换热对航天器的影响,从而确定主要的控温途径.在调研火星表面辐射、大气等热环境的基础上,从线性化传热系数和对流辐射比的角度对比分析了辐射、对流和导热对航天器的影响.器表辐射传热系数随光学属性和温度的变化范围...     

Modeling the meteoric dust effect on the equatorial electrojet

Dust particles of meteoric origin in the lower E-region can affect the conductivity parameters by varying the effective collision frequency and by causing electron bite outs through the capture of ambient electrons. In magnetized plasma, neutral dust particles can alter the effective collision frequency parameters and thus affect the Pedersen and Hall conductivities in the electrojet region. The Cowling conductivity profile is determined by the height profiles of the Hall and Pedersen conductivities. The collision parameters altered by the neutral dust particles can be considerably different from those estimated from atmospheric models, in the lower E-region heights where dust particles of meteoric origin are known to exist in large numbers. A significant fraction of these dust particles may capture free electrons from the ambient medium and get charged negatively. This can result in reduction in the number density of free electrons especially below the electrojet peak where the dust particles can be present in large numbers, at least on days of large meteor showers. This, in turn, can once again alter the vertical profile of the east–west Hall current driven by the vertical Hall polarization field and under favorable conditions, can even account for the reversal of the electrojet currents below the current peak. Assuming a realistic model for the distribution of neutral dust particles, the conductivity parameters are estimated here. Conditions under which the dust particles can cause partial reversals in the electrojet currents are critically examined here.     

Development of a micro-balance system for dust and water vapour detection in the Mars atmosphere

Quartz crystal piezoelectric sensors are suitable for deposition analyses that need very high sensitivity. Due to the wide working ranges and high performances, micro-balances can measure the mass settling in average Mars conditions during a period of months before saturation is reached. This ensures a proper use for short and long term water and dust deposition monitoring. Micro-balances have been studied, calibrated and used for the GIADA (grain impact analyser and dust accumulator) experiment for the ESA-Rosetta space mission. Experience on micro-balance performance study by dust deposition has been acquired and water vapour deposition studies are in progress in a Martian atmosphere simulation chamber. Preliminary results show that micro-balances are capable to detect up to partial pressure values corresponding to parts per billion of the typical Martian atmosphere.     

摄动因素对火星环绕段轨道长期影响研究

针对未来火星探测需要,研究了摄动因素对火星环绕段轨道的长期影响。对各种摄动因子的数量级进行了估计,根据估计结果,对比选取了起主导作用的摄动因子;建立了主要摄动因子的数学模型;通过数值仿真验证,对比分析了火星和地球的相应摄动因素对各自环绕段轨道半长轴和偏心率的影响。仿真结果表明:非球形摄动对火星环绕段轨道的影响具有明显的长周期特征,而相应的地球环绕段短周期效应较明显,这主要是由于质量分布不同造成火星非球形引力位中田谐项的系数基本都比地球的相应值大一个量级,因此在实际轨道设计中应该重点考虑高阶项特别是高阶田谐项对环绕段轨道造成的影响。     

The effect of the space flight environment on mucin production in the mouse uterine tube

Numerous studies have indicated that the microgravity environment of space has harmful effects on several tissues throughout the body. Although this phenomenon is well documented, research in this area is still in its relative infancy. This study investigates the effects of space flight on mucin production of the uterine tubes of mice. This study examined the epithelium of the uterine tubes from female mice that were flown on the space shuttle Endeavour for 13 days in August, 2007 and their concomitant controls. The tissue was qualitatively analyzed for the type of mucin produced, i.e., acidic, neutral, acidic/neutral mixture. Further, the tissue was quantitatively analyzed for the amounts of mucins produced by measuring the thickness of the mucin layer for each region of the uterine tube: isthmus, ampulla, and infundibulum. One way ANOVA tests were used to compare mucin thickness between all three sets of animals. Results indicate similar but not identical results between the three regions of the uterine tube. The Baseline tissue had the thickest mucin layer regardless of treatment group. In the ampulla the mucin layer was the thinnest in the Flight tissue, followed by the Ground Control, with the Baseline being the thickest. Analysis of the mucin layer of the infundibulum of the three treatment groups indicated no difference in its thickness between the three regions of the uterine tube. These results indicate a trend toward thinning of the mucin layer of the uterine tube in space flight, but also indicate an influence by the housing environment.     

月球受光面上月尘静电浮扬特性分析

基于单粒子轨道理论及空间尘埃等离子体充电方程,建立了月球受光面上尘埃微粒的静态荷电模型.基于光电子能量Maxiwellian分布假设,确定了月面垂直空间电场强度和光电子鞘层内带电粒子密度的函数表达式.利用牛顿运动定律和静电场力表达式,构建了月球受光面上尘埃微粒的静电浮扬动力学模型,并进行月尘静态浮扬特性的数值计算.研究结果显示:太阳高度角与颗粒粒径是控制月尘静电浮扬发生及动力学特性的两个基本参量;月尘静电浮扬发生在月球的黎明和黄昏;随着粒径的减少,月尘颗粒的最大浮扬高度不断增加.