Dosimetric results on EURECA.

Detector packages were exposed on the European Retrievable Carrier (EURECA) as part of the Biostack experiment inside the Exobiology and Radiation Assembly (ERA) and at several locations around EURECA. The packages consist of different plastic nuclear track detectors, nuclear emulsions and thermoluminescence dosimeters (TLDs). Evaluation of these detectors yields data on absorbed dose and particle and linear energy transfer (LET) spectra. Behind a shielding thickness in front of the detectors of 0.09g cm-2 the doses range between 21.26 Gy and 0.87 Gy depending on the location of the dosimeter. Not all measurement can be explained by calculations.     

Development of in-situ Space Debris Detector

Due to high relative velocities, collisions of spacecraft in orbit with Space Debris (SD) or Micrometeoroids (MM) can lead to payload degradation, anomalies as well as failures in spacecraft operation, or even loss of mission. Flux models and impact risk assessment tools, such as MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) or ORDEM (Orbital Debris Engineering Model), and ESABASE2 or BUMPER II are used to analyse mission risk associated with these hazards. Validation of flux models is based on measured data. Currently, as most of the SD and MM objects are too small (millimeter down to micron sized) for ground-based observations (e.g. radar, optical), the only available data for model validation is based upon retrieved hardware investigations e.g. Long Duration Exposure Facility (LDEF), Hubble Space Telescope (HST), European Retrievable Carrier (EURECA). Since existing data sets are insufficient, further in-situ experimental investigation of the SD and MM populations are required. This paper provides an overview and assessment of existing and planned SD and MM impact detectors. The detection area of the described detectors is too small to adequately provide the missing data sets. Therefore an innovative detection concept is proposed that utilises existing spacecraft components for detection purposes. In general, solar panels of a spacecraft provide a large area that can be utilised for in-situ impact detection. By using this method on several spacecraft in different orbits the detection area can be increased significantly and allow the detection of SD and MM objects with diameters as low as 100 μm. The design of the detector is based on damage equations from HST and EURECA solar panels. An extensive investigation of those panels was performed by ESA and is summarized within this paper. Furthermore, an estimate of the expected sensitivity of the patented detector concept as well as examples for its implementation into large and small spacecraft are presented.     

Crystallisation of alpha-crustacyanin, the lobster carapace astaxanthin-protein: results from EURECA.

Crystallisation of alpha-crustacyanin, the lobster carapace astaxanthin-protein was attempted under microgravity conditions in EURECA satellite using liquid-liquid diffusion with polyethyleneglycol (PEG) as precipitant; in a second reaction chamber phenol and dioxan were used as additives to prevent composite crystal growth. Crystals of alpha-crustacyanin grown under microgravity from PEG were larger than those grown terrestrially in the same apparatus under otherwise identical conditions. On retrieval, the crystals from PEG were shown to be composite and gave a powder diffraction pattern. The second reaction chamber showed leakage on retrieval and had also been subjected to rapid temperature variation during flight. Crystal fragments were nevertheless recovered but showed a powder diffraction pattern. It is concluded, certainly for liquid-liquid diffusion using PEG alone, that, for crustacyanin, although microgravity conditions resulted in an increase in dimensions of crystals, a measurable improvement in molecular ordering was not achieved.     

Recent results of comparative radiobiological experiments with short and long term expositions of arabidopsis seed embryos

Comparison of experimental data obtained from short (SDEF) and long duration exposure flights (LDEF) recently led to results, which will contribute for the estimation of genetic risk for long and/or repeated stay of man in space. Under orbital conditions biological stress and damage are induced in test subjects by cosmic radiation, especially the high energetic, densely ionizing component of heavy ions. Plant seeds were successful model systems for a biotest in studying the physiological damages and mutagenic effects caused by ionizing radiation in particular stem cells. In this article we present an overview of our space experiments with Arabidopis thaliana seeds. We present first results of investigations on certain damage endpoints (seed germination, plant survival, mutation frequencies), caused by cosmic ionizing radiation in dry dormant plant seeds of Arabidopsis thaliana after different short term (e.g. IML-1 and D-2) and long term (e.g. EURECA and LDEF-1) space exposures. Total dose effects of heavy ions and the other components of the mixed radiation field on damage endpoints and survival after space exposure and gamma-ray preirradiation were obtained. A new method of total dose spectrometry by neutron activation has been applied.     

EURECA and SGF performances

The EURECA platform offers unique characteristics for microgravity research: a very low level micro-gravity spectrum and a long operation time for recoverable experiments.

Five core facilities on board will perform an impressive number of experiments. The main purpose of the Solution Growth Facility (SGF) is growing crystals at low temperatures by using the double diffusion technique in three compartment reactors. The micro-gravity eliminates the convection in the liquid, while Marangoni convection is avoided by the absence of free surfaces. The thermal gradient in the buffer zone is better than 0.01°C/cm. Turbulence is eliminated by control of the valve rate and by a pressure compensation system. All surfaces are coated with Halar. The diffusion rate can be controlled by the use of filters. The SGF contains three independently controlled reactors.

A forth reactor contains an experiment aiming at measuring the Soret coefficient of twenty binary organic mixtures and aqueous electrolyte solutions.     

Biological responses to space: results of the experiment "Exobiological Unit" of ERA on EURECA I.

Spores of different strains of Bacillus subtilis and the Escherichia coli plasmid pUC19 were exposed to selected conditions of space (space vacuum and/or defined wavebands and intensities of solar ultraviolet radiation) in the experiment ER 161 "Exobiological Unit" of the Exobiology Radiation Assembly (ERA) on board of the European Retrievable Carrier (EURECA). After the approximately 11 months lasting mission, their responses were studied in terms of survival, mutagenesis in the his (B. subtilis) or lac locus (pUC19), induction of DNA strand breaks, efficiency of DNA repair systems, and the role of external protective agents. The data were compared with those of a simultaneously running ground control experiment. The survival of spores treated with the vacuum of space, however shielded against solar radiation, is substantially increased, if they are exposed in multilayers and/or in the presence of glucose as protective, whereas all spores in "artificial meteorites", i.e. embedded in clays or simulated Martian soil, are killed. Vacuum treatment leads to an increase of mutation frequency in spores, but not in plasmid DNA. Extraterrestrial solar ultraviolet radiation is mutagenic, induces strand breaks in the DNA and reduces survival substantially; however, even at the highest fluences, i.e. 3 x 10(8) J m-2, a small but significant fraction of spores survives the insolation. Action spectroscopy confirms results of previous space experiments of a synergistic action of space vacuum and solar UV radiation with DNA being the critical target.     

UV photobiochemistry under space conditions

The response of spores of Bacillus subtilis, cells of Deinococcus radiodurans and conidia of Aspergillus ochraceus to actual and simulated space conditions (UV in combination with long-term exposure to extremely dry conditions, including vacuum) has been studied: The following effects have been analyzed: decrease of viability, occurrence of DNA double strand breaks, formation of DNA-protein cross-links and DNA-DNA cross-links. All organisms show an increased sensitivity to UV light in extreme dryness (dry argon or vacuum) compared to an irradiation in aqueous suspension. The UV irradiation leads in all cases to a variety of DNA lesions. Very conspicuous is the occurrence of double strand breaks. Most of these double strand breaks are produced by incomplete repair of other lesions, especially base damages. The increase in DNA lesions can be correlated to the loss in viability. The specific response of the chromosomal DNA to UV irradiation in extreme dryness, however, varies from species to species and depends on the state of dehydration. The formation of DNA double strand breaks and DNA-protein cross-links prevails in the case of B. subtilis spores. In cells of Deinococcus radiodurans DNA-DNA cross-links often predominate, in conidia of Aspergillus ochraceus double strand breaks. The results obtained by direct exposure to space conditions (EURECA mission and D2 mission) largely agree with the laboratory data.     

Proposed lunar-based telescopes for NEO observations

The first lunar-based telescope for a test of NEO observations is discussed within a scenario of NASDA's sequence of lunar missions. There have been no real telescopes on the moon as yet, and therefore we have to step up from a primitive level of telescope to real NEO telescopes. The first telescope with an aperture of 30 cm is expected to be launched around 2005.     

The Geostationary Earth Radiation Budget Edition 1 data processing algorithms

The Geostationary Earth Radiation Budget (GERB) instrument is the first to measure the earth radiation budget from a geostationary orbit. This allows a full sampling of the diurnal cycle of radiation and clouds – which is important for climate studies, as well as detailed process studies, e.g. the lifecycle of clouds or particular aerosol events such as desert storms. GERB data is now for the first time released as Edition 1 data for public scientific use. In this paper we summarise the algorithms used for the Edition 1 GERB data processing and the main validation results. Based on the comparison with the independent CERES instrument, the Edition 1 GERB accuracy is 5% for the reflected solar radiances and 2% for the emitted thermal radiances.     

Initial results from COMPTEL onboard GRO

COMPTEL is the first imaging telescope to explore the MeV gamma-ray range (0.7 to 30 MeV). At present, it is performing a complete sky survey. In later phases of the mission selected celestial objects will be studied in more detail. The data from the first year of the mission have demonstrated that COMPTEL performs very well. First sky maps of the inner part of the Galaxy clearly identify the plane as a bright MeV-source (probably due to discrete sources as well as diffuse radiation). The Crab and Vela pulsar lightcurves have been measured with unprecedented accuracy. The quasars 3C273 and 3C279 have been seen for the first time at MeV energies. Both quasars show a break in their energy spectra in the COMPTEL energy range. The 1.8 MeV line from radioactive ²⁶A1 has been detected from the central region of the Galaxy and a first sky map of the inner part of the Galaxy has been obtained in the light of this line. Upper limits to gamma-ray line emission at 847 keV and 1.238 MeV from SN 1991T have been derived. Upper limits to the interstellar gamma-ray emissivity have been determined at MeV-energies. Several cosmic gamma-ray bursts within the field-of-view have been located with an accuracy of about 1°. On 1991 June 9, 11 and 15, COMPTEL observed gamma-ray emission (continuum and line) from three solar flares. Also neutrons were detected from the June 9 and June 15 flares.     

Design and construction of the ROSAT 5 arcsec mirror assembly

The ROSAT mission, which is currently being prepared in W.-Germany, will perform the first soft X-ray all-sky survey by means of a large imaging X-ray telescope. Detailed calculations under the cost, volume and mass constraint of the satellite being a Shuttle payload have led to a design of the imaging optics with optimized geometry. The mirror system is of the Wolter type I configuration and includes four nested shells with a maximum aperture of 835 mm and a focal length of 2400 mm. The on-axis angular resolution of the mirror assembly has been specified to 5 arcsec with a scattering level as low as 3% for single reflection at 1.5 keV photon energy. Construction and technology studies have been completed by now and manufacturing of the first mirror shell has begun.     

The evolution of the central component in SN 1986J

The unusual core-collapse supernova 1986J, in the nearby spiral NGC 891, is the first modern supernova in which evidence of a compact remnant of the supernova has been seen. This evidence comes from recent VLBI images, which show the emergence of a new radio component in the center of the expanding radio shell. The new component shows an inverted radio spectrum contrasting with that of the shell. The new component is likely radio emission associated with the black-hole or neutron star compact remnant of the explosion, which would mark the first direct observational link between a modern supernova and such a compact remnant. We report here on our recent VLBI images at 22 and 5 GHz, as well as on our monitoring of the integrated radio spectrum of SN 1986J. In the 22 GHz image, the central component is marginally resolved.     

钛合金冲击性能与动态压缩性能间的定量关系

为认识钛合金的冲击性能与冷镦成品率的关系,运用组织定量统计分析的方法研究了Ti-3Al-5Mo-4.5V钛合金显微组织参数对冲击性能的影响规律,结合动态压缩后的剪切带宽度变化规律,探讨了裂纹形成功、裂纹扩展功以及冲击功与剪切带宽度之间的关系.结果表明:随着退火温度的上升,α片长宽比先增加后减小,裂纹形成功也是先上升后下降,而裂纹扩展功却是先减小后增加,冲击总功持续上升;冲击功指标与材料的动态压缩性能未发现必然联系,裂纹形成功与动态压缩后的剪切带宽度成反比例关系,而裂纹扩展功与剪切带宽度线性正相关.      

钇、钡、铜氧化物超导体在微重力条件下的热处理试验研究

论述利用我国返回式卫星,在其搭载的晶体加工炉中,首次完成的钇、钡、铜氧化物超导体样品的空间热处理试验。     

敏捷性飞机飞行控制系统设计方法研究

对敏捷性飞机飞行控制系统的设计方法进行了研究,研究表明当飞机进行大迎角机动时,飞机可以获得敏捷性机动能力,在这种情况下,飞机的动力学特性呈现非线性的特征,此时飞行控制系统的设计是一类非线性控制系统的设计问题,设计可采用非线性动态逆的方法进行,为简化控制律和工程因素,重点研究了利用一阶动态作为系统的反馈线性控制,以得到线性化的系统,在此基础设计跟踪控制器,以满足大迎角非线性机动时的性能要求,最后以Ｆ     

Solar radio emissions

In this paper, we present a tutorial review which was presented at the first Advanced School on Space Environment (ASSE 2004). We first describe the basics of radioastronomy definitions, and discuss radiation processes relevant to solar radio emissions like plasma emission, free–free bremsstrählung and gyromagnetic emissions. We illustrate these fundamentals by describing recent solar radio observations and the constraints they bring on different solar physical parameters. We focus on solar radio emissions from the quiet sun, active regions and during explosive events known as solar flares, and how the latter can bring quantitative informations on the particles responsible for the emission. Finally, particular attention is paid to new radio diagnostics obtained at very high frequencies in the millimeter/submillimeter range, as well as to radio emissions relevant to Space Weather studies.     

空间相机桁架支撑结构满应力优化设计与试验

针对空间相机桁架式支撑结构在设计过程中难以同时保证重量轻且刚度高的问题, 提出了采用满应力方法对桁架杆截面进行优化设计的思想. 以桁架杆重量最低为优化目标, 桁架杆自重变形和桁架的一阶固有频率为约束条件, 桁架杆截面的内外径为优化变量, 建立了基于满应力准则的优化模型. 经过优化, 桁架杆截面的外径为50mm, 内径40mm, 质量6.1kg, 一阶固有频率121Hz. 采用有限元法对优化结果进行模态校核和重力变形校核, 同时为检验碳纤维复合材料的热稳定性, 对桁架组件进行了热变形分析, 得到次镜的偏心和偏转均满足光学设计要求. 对优化设计出的桁架组件进行了0.2g扫频试验以及尺寸稳定性试验. 试验结果表明, 桁架组件一阶固有频率119Hz 与理论分析结果基本吻合; 在45N外力载荷和15°C均匀温升载荷的作用下, 桁架稳定性能良好, 次镜的偏心和偏转均小于5", 满足光学设计要求. 优化设计出的桁架支撑结构具有刚度高、尺寸稳定等特点, 这为实现空间相机向大口径、长焦距、轻型化方向发展奠定了研究基础.      

Impact of geomagnetic storm of September 7–8, 2017 on ionosphere and HF propagation: A multi-instrument study

The present study reveals the features of ionospheric parameters variations during the geomagnetic storm of September 7–8, 2017. In particular, parameters of vertical (foF2, foEs) and oblique ionospheric sounding (MOF, modes), absorption level, Total Electron Content (TEC) and particle fluxes at high altitudes were under analysis. The storm was characterized by two Dst-index mimima and can be considered as a sequence of two storms: first - with Dstmin?=??142?nT at 02 UT on September 8th and second - with Dstmin?=??122?nT and at 15 UT on September 8th. It was found that these two storms had different impacts on the ionosphere and HF propagation at mid- and high-latitudes of Northern Hemisphere. The signals of vertical and oblique ionospheric sounding were present in all ionograms before the first storm. Further, at the maximum of the first storm these signals were totally absorbed. Then, before the second storm and during its maximum the signals were detected again in the ionograms due to the low absorption. GOES satellite data showed the significant burst of electrons and protons only during the first storm and small particle fluxes - during the second storm. This feature was also confirmed with GPS data: TEC increased during the first storm and decreased during the second storm.     

机群环境中基于信度模型的作业调度算法

提出了一种新的机群环境下的作业调度算法,该算法基于信度模型.在信度模型 中,每一个计算节点是一个信度实体,系统根据信度实体的物理能力、当前状态、历史作业完成情况,对节点进行信度评价,赋予其相应的信度值,调度算法根据信度实体信度值为作业分配合适的资源运行作业.同时,调度系统还对机群系统的整体信度进行评价,并根据估计的作业运行时间和完成期限对作业做信度要求折算,调度系统根据机群系统的整体信度情况和作业信度要求来决定是否接受该作业请求.在OpenPBS机群调度系统上实现了该算法,并通过GridSim工具包与先入先出FIFO(First Input First Output) 算法和Libra调度算法进行了模拟对比试验.试验结果表明,该算法是有效的.      

采用DSG技术实现零件模型分解

针对回转体和箱体类零件模型,应用分解性实体几何技术实现零件设计模型到制造模型的有序分解,介绍了基于特征树模型的两个关键算法:宽度优先和深度优先搜索,以完成面向特征加工过程的空间和时间域内的制造过程规划.最后用一个详细的算例进一步陈述零件模型分解技术.