火箭发动机推力瞬变的测量

任何测力装置都能用一个质量弹簧系统来描述,最简单地说:即通过一个具有刚度 K 和质量 M 的简单弹簧来描述,其中它的阻尼为 c,位移为 x,于是有M(d~2x/dt~2) c(dx/dt) kx=T,这里 T 为外加力。而大多数系统只测量 kx 项,这对低频情况是足够的。为了精确地记录推力的变化,从而要提高装置的固有频率,使之相对于推力变化的频率来说足够高,有时这是不现实的。为克服这一困难有两种可采用的途径。第一种方法是把运动方程的所有项合并到远远超过装置的固有频率所给定外力上。第二种方法是一个质量块在沿轴向作用的轴承上被发动机自由加速,加速度计给出推力/时间曲线。通过使质量块停止所需要的力对所预定时间内的积分而得到总冲。     

碳/碳复合材料

引言近年来,欧洲动力公司(S.E.P.)对固体发动机喷管部件所用的碳材料,特别是碳/碳材料进行了研制。喷管材料具有耐烧蚀的特性,要经受3000℃以上的高温。由于喷管性能要求非常高,材料必须具有良好的耐烧蚀性能和较低的比重。考虑到在大多数喷管里,化学反应发生在还原介质中,我们认为所能使用的耐热材料中,碳是最可取的。在此文中,我们不评述构成喷管部件的碳结构材料,只简要地论述多晶石墨、热解石墨、碳增强酚醛复合材料和碳/碳材料,侧重介绍后两种,这是欧洲动力公司重点研制项目。     

论现有远地点发动机用于新航天飞行器的有关问题

为了使正进入鉴定阶段的远地点发动机(TE-M-616)用于广播试验卫星,本文介绍了该新航天飞行器对远地点发动机的各系统及分系统提出的要求。由于加拿大通讯技术卫星和广播试验卫星对远地点发动机在环境和性能要求上有所不同,为了解决此问题,必须使远地点发动机经受住最恶劣的环境。喷管设计以及远地点发动机与航天器的对接都利用现有设计结构。根据对远地点发动机分析的结果,已经表明,若保持安全系数不变,只需要对现在进行的试验计划做一些修改和补充。另一方面,对于航天器提出的技术条件必须进一步审核,以便使新航天飞行器设计有最大可能利用现有的远地点发动机。     

一种大变形多空间域连续体结构拓扑优化方法

针对大变形非线性结构拓扑优化问题,提出了基于混合细胞自动机(HCA, Hybrid Cellular Automata)多空间域连续体结构拓扑优化方法;采用密度法,建立了单元相对密度表示的材料弹-塑性模型;以单元相对密度和应变能作为细胞自动机(CA,Cellular Automata)的状态信息,利用CA局部控制规则,修改相对密度,迭代实现各设计空间域应变能均匀分布;设计了多空间域拓扑优化HCA算法,采取多个对象同时耦合优化迭代,各自收敛策略,解决了多空间域优化迭代算法收敛稳定性问题;最后,以汽车保险杆结构横梁和支撑等两个设计空间为例,施加大变形动态载荷作用,对提出的多空间结构优化算法进行了验证,优化后结构有效地降低了碰撞作用力峰值达54％,提高了结构安全性.     

DS/FH混合扩频快速捕获技术的研究

在DSFFH混合扩频通信系统中,快速捕获是一个非常关键的技术。通过采用快速扫描和等待式相结合的方法用来实现跳频信号的快速捕获,利用神经网络技术实现直扩信号的快速捕获,通过这2种方式,就可实现DSFFH混合扩频的快速捕获。     

The Dynamic Albedo of Neutrons (DAN) experiment for NASA's 2009 Mars Science Laboratory

We present a summary of the physical principles and design of the Dynamic Albedo of Neutrons (DAN) instrument onboard NASA's 2009 Mars Science Laboratory (MSL) mission. The DAN instrument will use the method of neutron-neutron activation analysis in a space application to study the abundance and depth distribution of water in the martian subsurface along the path of the MSL rover.     

Searching for life on Mars: selection of molecular targets for ESA's aurora ExoMars mission

The European Space Agency's ExoMars mission will seek evidence of organic compounds of biological and non-biological origin at the martian surface. One of the instruments in the Pasteur payload may be a Life Marker Chip that utilizes an immunoassay approach to detect specific organic molecules or classes of molecules. Therefore, it is necessary to define and prioritize specific molecular targets for antibody development. Target compounds have been selected to represent meteoritic input, fossil organic matter, extant (living, recently dead) organic matter, and contamination. Once organic molecules are detected on Mars, further information is likely to derive from the detailed distribution of compounds rather than from single molecular identification. This will include concentration gradients beneath the surface and gradients from generic to specific compounds. The choice of biomarkers is informed by terrestrial biology but is wide ranging, and nonterrestrial biology may be evident from unexpected molecular distributions. One of the most important requirements is to sample where irradiation and oxidation are minimized, either by drilling or by using naturally excavated exposures. Analyzing regolith samples will allow for the search of both extant and fossil biomarkers, but sequential extraction would be required to optimize the analysis of each of these in turn.     

Spectral properties of Lake Superior banded iron formation: application to Martian hematite deposits

Several locations have been identified on Mars that expose bulk, coarsely crystalline gray hematite. These deposits have been interpreted as being sedimentary and formed in aqueous environments. Lake Superior Type (LST) banded iron formation (BIF) was investigated as a spectral and possible process analog to these deposits. In northern Michigan, LST BIF formed in a sedimentary, continental shelf or shallow basin environment under stable tectonic conditions, and the oxide facies contains gray, crystalline hematite. These deposits are Proterozoic in age and contain microfossils associated with the early diversification of life on Earth. Samples of the hematite-bearing oxide facies, as well as the carbonate facies, were collected and analyzed for their spectral and geochemical characteristics. Sample spectra were measured in the visible, near-infrared, and thermal infrared for comparison with remote and in situ spectra obtained at Mars. Thin section analysis, as well as X-ray diffraction and scanning electron microscopy measurements, were performed to determine detailed geochemistry. There is no evidence for BIF at Opportunity's Meridiani landing site, and the results of this work will provide useful data for determining whether BIFs exist elsewhere on Mars and are, thus, relevant to current and future Mars exploration missions.     

The Physical Foundation of Forecasting Disturbances in the Geospace From Solar Disk Characteristics

The five main types of antisunward propagating energetic fluxes (particles and emission) may be thought of as well established to date, the effects of which lead to a particilar character of disturbance in the near-terrestrial environment (the Earth's magnetosphere, ionosphere and atmosphere). The strongest global restructuring of the magnetosphere and ionosphere is caused by fluxes of relatively dense n of 1-70 cm-3 at the Earth's orbit) Solar Wind (SW) quasi-neutral, low-energy (E ＜ 10 keV) plasma which cause magnetospheric and ionospheric storms lasting 24 hours or longer. For that reason, main attention is given to their study at the initial stage of research. The physical essence of the method of predicting disturbances in the near-terrestrial space environment, the amplitude of which can be expressed in, for example, the Kp index units, involves:(1) identifying all the most geo-effective SW streams of type, (2) determing their sources on the solar disk,and (3) quantifying the correlations between the characteristics of their solar sources with a maximum value of the Kp-index that is caused by the concerned type of SW stream. Semi-phenomenological relations have been obtained, which relate parameters of type SW stream sources to characteristics of geomagnetic storms:storm commencement, the time at which the storm intensity reaches its maximum values, the storm duration,as well as to the storm amplitude expressed in terms of geomagnetic indeces.