阿里安火箭将进行第64次发射

英国国防部将于１９９４年６月发射两颗小卫星，用于检验有关太阳能收集、耐辐射和星上计算方面的试验技术。这两颗卫星，每颗重约５０公斤，设计寿命为一年，它们将和Ｉｎｔｅ１ｓａｔ－７０２通信卫星一起由阿里安－４火箭发射进入地球同步转移轨道。Ｉｎｔｅ１ｓａｔ－７０２通信卫星是由位于加利福尼亚州的帕洛阿尔托的空间系统／Ｌｏｒａｌ公司制造的，该卫星最后进入位于赤道上空的地球同步轨道的定点位置。这两颗英国卫星将运行在穿过地球的范艾伦辐射带的大椭圆转移轨道上。阿里安空间公司的商业发射合伙人期望这次发射安排在１９９…     

日研制气象卫星用高性能红外CCD器件

日本三菱电机公司从宇宙开发事业团(NASDA)获得试制红外用电荷耦合器件(IRCCD)的基础技术,这是军对民的大型技术转移。该技术是NASDA和筑波大学共同研究的,它是一种能探测所需波长为10微米频带的高性能红外CCD器件。 1987年,NASDA首次将器件技术向私营企业转移,东芝、日本电     

地球同步轨道卫星混合推进转移轨道特性分析

以地球同步轨道卫星转移轨道设计为背景，针对全化学推进燃料消耗大和全电推进转移时间长的问题，开展了化学 电混合推进转移轨道优化设计与特性分析。首先，讨论了轨道倾角和近地点幅角变化对混合推进转移轨道的影响。研究表明，在混合推进优化设计中需要将轨道倾角作为优化变量之一。然后，以近地点半径、远地点半径、轨道倾角为优化变量生成搜索网格，得到过渡轨道集。针对每条过渡轨道，构建化学推进转移段和电推进转移段。其中化学推进段采用单圈兰伯特转移解算，电推进段采用混合法优化。最后，以燃料消耗和转移时间为指标，在搜索域内开展解算分析，研究了混合推进轨道在整个搜索域内的变化趋势。该方法可以提供具有不同燃料消耗和转移时间的混合推进转移解集，拓宽了解空间，可供轨道设计人员根据任务约束灵活选用。     

美国将发展编队监视卫星

美国空军和国防高级研究计划局将研究利用一组微型卫星来取代大卫星执行空间监视等任务。他们正在为“技术卫星-21”(TechSat-21)微型卫星计划的基础研究向工业界征求建议,以减少系统质量和成本。     

欧空局拟打造数据中继星座

为保持欧洲的独立性，并改善“欧洲静地导航重叠业务”这一“伽利略”的增强系统的可靠性和安全性，欧空局准备向其成员国建议兴建一个“欧洲数据中继卫星系统”（EDRSS）。该系统将是一个由3颗静地轨道卫星构成的星座，首颗卫星拟于2012年发射。日前升空的欧空局的“自动转移飞行器”（ATV）货运飞船将采用美国的“跟踪与数据中继卫星系统”（TDRSS），     

向月飞行轨道的若干特性研究

利用圆锥曲线拼接技术，研究从地球圆形停泊轨道飞向月球的轨道及月球卫星轨道的轨道特性，当地月转移轩道平面与月轨道平面共面时，月心轨道和地月转移轨道射入条件的关系可用一组代数方程描述，不共面时，可用一组超越方程迭代求解，数字仿真得到了有益结论。     

个人卫星通信受到蜂窝电话系统的威胁

蜂窝电话服务系统一旦进行为高规格商务个体的高额投入，它将迅速成为许多工业界，包括以陆地移动卫星通信系统为依托的用户的主要通信工具。今天，蜂窝电话系统在陆地上已迅速向跨国区域扩展，那是和蜂窝电话工业推出增强的蜂窝电话数据传输技术结合在一起的。它以蜂窝电话网络来进行数据包的传输，已极大地冲击了陆地移动卫星通信的服务市场。如不出现例外，蜂窝电话系统将与陆地移动卫星通信系统发生激烈的竞争。美国华盛顿特区从事卫星通信业务的马可公司（Ｍａｒｃｏｒ）经理马丁·罗斯伯拉塔说，马可公司在１９９１年在装备美国达拉斯…     

气动力辅助椭圆轨道转移技术研究

研究了两种共面椭圆轨道最优转移方法--基于单纯推力的双脉冲对称转移和基于气动力辅助变轨技术的协同机动方法。推导了双脉冲对称转移问题中转移椭圆轨道的求解公式,采用遗传算法求解最优变轨点位置,给出了变轨脉冲的计算方法。将气动力辅助对称转移过程分为3段：真空飞行段、大气飞行段、真空飞行段。以能量最小为性能指标,将大气飞行段轨迹优化问题转化为标准最优控制问题模型,并利用Gauss伪谱法进行求解,得到“巡航+滑行+巡航+滑行”的大气最优飞行轨迹。最后对两种转移方法进行详细比较,指出初始椭圆轨道近地点越接近大气层,气动力辅助对称转移方法比双脉冲对称转移方法越节省能量。     

美国集中力量发展GPS系统

美国联邦航空局（ＦＡＡ）已终止进一步研制微波着陆系统（ＭＬＳ），以便集中力量发展ＧＰＳ着陆系统。ＦＡＡ终止ＭＬＳ的研制是因为其价格昂贵，而且ＧＰＳ技术发展迅速。当前，ＩＬＳ精密进场系统仍将继续使用，在基于ＧＰＳ的着陆系统投入使用之前，美国将不会放弃ＩＬＳ。ＦＡＡ已通知国际民航组织（ＩＣＡＯ），将取消从１９９８年１月开始在国际机场安装ＭＬＳ的承诺。ＦＡＡ已开始进行Ⅲ类ＧＰＳ着陆的可行性研究，这些研究将于１９９５年２月完成。ＦＡＡ在ＧＰＳ着陆的研究方面在世界上领先。尽管ＧＰＳ着陆的适用性还有待证明，…     

美科学家呼吁停止为部署拦截弹拨款

22位美国顶尖科学家4月7日呼吁国会别再为部署地基导弹防御系统的拦截弹拨款，称该系统无法实现对真实攻击的防御。他们在一封信中说，在该系统能通过模拟真实条件的试验来证明其能力之前，拨款应被取消。他们认为，在缺乏真实而成功的试验的情况下就宣布将其投入使用并进一步部署是没有技术依据的。这些科学家中有9位诺贝尔物理学奖得主，     

Scaling analysis and model estimation of solar corona index

A monthly average solar green coronal index time series for the period from January 1939 to December 2008 collected from NOAA (The National Oceanic and Atmospheric Administration) has been analysed in this paper in perspective of scaling analysis and modelling. Smoothed and de-noising have been done using suitable mother wavelet as a pre-requisite. The Finite Variance Scaling Method (FVSM), Higuchi method, rescaled range (R/S) and a generalized method have been applied to calculate the scaling exponents and fractal dimensions of the time series. Autocorrelation function (ACF) is used to find autoregressive (AR) process and Partial autocorrelation function (PACF) has been used to get the order of AR model. Finally a best fit model has been proposed using Yule-Walker Method with supporting results of goodness of fit and wavelet spectrum. The results reveal an anti-persistent, Short Range Dependent (SRD), self-similar property with signatures of non-causality, non-stationarity and nonlinearity in the data series. The model shows the best fit to the data under observation.     

Stochastic particle acceleration by the forced interaction of relativistic current sheets

We address the problem of interacting relativistic current sheets in self-consistent kinetic plasma simulations within the framework of the Particle-In-Cell model. The interaction is enforced in head-on collisions of up to 10 current sheets at relativistic bulk speeds. The simulations are motivated by the general problem of Poynting flux dissipation in ‘striped wind’ configurations presumably governing the relativistic outflows pervasive in pulsar winds and gamma-ray bursts. We identify the generation of non-thermal particles and formation of a stable power-law shape in the particle energy distributions f(γ) dγ ∝ γ^−s dγ. In 1D, a spectral index s ∼ 2 is observed and attributed to a stochastic Fermi-type acceleration mechanism. In 2D, the generic index of s ∼ 3–4 is retained as in previous simulations of individual current sheets. Whereas in 2D the high energy cut-off is constrained by the limited dissipation of magnetic energy, in 1D the process converts the bulk motion of current sheets towards directed particle momentum of an exclusive class of non-thermal particles.     

Development of a gas chromatography compatible Sample Processing System (SPS) for the in-situ analysis of refractory organic matter in martian soil: preliminary results

In the frame of the 2009 Mars Science Laboratory (MSL) mission a new sample preparation system (SPS) compatible with gas chromatography–mass spectrometry (GC–MS) has been developed for the in situ analysis of complex organic molecules in the Martian soil. The goal is to detect, if they exist, some of the key compounds that play an important role in life on Earth including carboxylic acids, amino acids and nucleobases.     

Concept options for the aerial survey of Titan

Various aerial platforms intended for long endurance survey of the Titan surface are presented. A few novel concepts are introduced, including a heated methane balloon and a balloon with a tethered wind turbine. All the concept options are predicted to have lower scientific payload fractions than the Huygens probe. It is concluded that the selection of the best aerial platform option depends on more accurate mass estimates and a clear decision on whether, or not, in situ surface composition measurements are required in conjunction with aerial remote sensing.     

Heterogeneous solid/gas chemistry of organic compounds related to comets,meteorites, Titan,and Mars: Laboratory and in lower Earth orbit experiments

To understand the evolution of organic molecules involved in extraterrestrial environments and with exobiological implications, many experimental programs in the laboratory are devoted to photochemical studies in the gaseous phase as well as in the solid state. The validity of such studies and their applications to extraterrestrial environments can be questioned as long as experiments conducted in space conditions, with the full solar spectrum, especially in the short wavelength domain, have not been implemented. The experiments that are described here will be carried out on a FOTON capsule, using the BIOPAN facility, and on the International Space Station, using the EXPOSE facility. Vented and sealed exposition cells will be used, which will allow us to study the chemical evolution in the gaseous phase as well as heterogeneous processes, such as the degradation of solid compounds and the release of gaseous fragments.     

基于LuGre模型的电液加载系统摩擦补偿

为了提高电液加载系统控制精度,针对摩擦问题提出了基于LuGre摩擦模型的前馈补偿方法.建立了用于摩擦仿真分析和补偿器设计的电液加载系统数学模型;通过实验获取并分析了相关的摩擦数据;基于实验数据进行LuGre模型参数辨识,把LuGre模型和辨识结果引入电液加载系统数学模型,并进行仿真结果与实际摩擦数据的对照,证明了LuGre摩擦模型的准确性.设计前馈补偿器,进行了实验对比,实验结果表明前馈补偿器可将摩擦产生的控制误差有效地降至未补偿时的30%左右.      

CoRoT and Kepler results: Solar-like oscillators

The space-borne observatories CoRoT (Convection Rotation and planetary Transits) and Kepler have provided photometric time series data of unprecedented precision for large numbers of stars. These data have revolutionized the fields of transiting exoplanets and asteroseismology. In this review some important asteroseismic results obtained using data from the CoRoT and Kepler space missions concerning stars that show solar-like oscillations are discussed. These results comprise, among others, measurements of the location of the base of the convection zone and helium second-ionization zone in main-sequence stars, the presence (or not) of core-helium burning in red-giant stars, as well as differential rotation in these stars.     

The ESA scientific programme

The ESA scientific programme has, so far, provided several significant astrophysics experiments and further important missions are scheduled for execution during the next decade. These missions are briefly summarised together with several astrophysics investigations presently under study.     

Return to Europa: Overview of the Jupiter Europa orbiter mission

Missions to explore Europa have been imagined ever since the Voyager mission first suggested that Europa was geologically very young. Subsequently, the Galileo spacecraft supplied fascinating new insights into this satellite of Jupiter. Now, an international team is proposing a return to the Jupiter system and Europa with the Europa Jupiter System Mission (EJSM). Currently, NASA and ESA are designing two orbiters that would explore the Jovian system and then each would settle into orbit around one of Jupiter’s icy satellites, Europa and Ganymede. In addition, the Japanese Aerospace eXploration Agency (JAXA) is considering a Jupiter magnetospheric orbiter and the Russian Space Agency is investigating a Europa lander.     

HELIO: The Heliophysics Integrated Observatory

Heliophysics is a new research field that explores the Sun–Solar System Connection; it requires the joint exploitation of solar, heliospheric, magnetospheric and ionospheric observations.