运载火箭末子级留轨应用平台研究综述

针对如何实现大量运载火箭末子级变废为宝的问题,本文对基于运载火箭末子级的留轨应用平台进行了综述。分别介绍了系统组成和工作模式、国内外研究现状等,总结了大惯量末子级精准钝化技术、轻质化末子级留轨应用平台总体技术、多约束下留轨应用平台合理布局技术、标准化载荷设计与试验技术等4项关键技术,并对留轨应用平台的未来发展进行了叙述。建议提升末子级留轨应用平台的搭载机会,逐步推动其在现役运载火箭上的广泛应用进行展望,按照能定姿、能调姿、能轨控的思路逐步提升其能力,促进留轨应用平台的规模化应用。

基于运载火箭末子级构建空间试验平台的有关思考

1概述。末子级是指运载火箭最后的一级,通常为第二级或第三级,主要用于将航天器送入目标轨道,并按照器箭接口约束完成航天器分离。当前大多数运载火箭末子级完成分离动作后即实施在轨钝化或有限离轨成为空间废弃物,在轨漂浮长达数年甚至数十年。由于航天器质量、尺寸不尽相同,相对固定的火箭运载能力,每次发射都会有少则几公斤、多则几十公斤的运载能力余量,为基于末子级留轨系统开展载荷在轨试验提供了宝贵机会。

火箭液体末子级精准钝化排放设计及飞行验证

火箭末子级搭载留轨应用系统是实现火箭末子级二次利用的重要手段,是空间资源利用的创新途径之一。为满足留轨应用系统在较小控制能力下具备快速在轨稳定应用的能力,本文围绕推进剂钝化排放机理开展仿真研究,设计了火箭末子级精准钝化排放飞行程序,改进了排放管路布局,从而降低留轨应用系统在自主控制前火箭的排放干扰,提供相对稳定的初始姿态条件。飞行试验结果表明:火箭末子级可为留轨应用系统俯仰、偏航、滚转通道提供0.4(°)/s以内的稳定姿态,优于留轨系统单轴1(°)/s的设计要求;排放程序设计合理、正确,排放管路改进有效,满足末子级钝化的要求。

运载火箭末子级推进剂钝化技术综述

运载火箭末子级推进剂钝化是指通过排空剩余推进剂,减小火箭末子级在轨解体的可能性。对运载火箭末子级推进剂进行钝化是减少空间碎片的重要措施。通过分析各种火箭末子级剩余推进剂排放方案的技术特点,总结提炼出剩余推进剂排放方案设计原则,能为后续新型运载火箭的研制提供技术参考。

末子级并联贮箱均衡输送对入轨精度影响研究

对液体运载火箭末子级并联贮箱推进剂输送不均衡量影响卫星入轨精度进行了研究。建立了均衡输送模型和星箭分离齿轮啮合模型,给出了质心横移计算公式。分析发现质心横移会因出现横向控制力矩而导致轨道倾角产生偏差,并对用弹簧分离实现的星箭分离形成干扰力矩而影响分离精度。以新一代运载火箭末子级为例,计算了不同膜片翻转压力偏差的输送不均衡量、质心横移量和卫星入轨精度偏差。结果发现:为满足卫星入轨精度,需控制金属膜片翻转压力偏差小于0.015MPa。翻转试验结果验证了此结论。

基于末子级应用的可重构通信载荷研究设想

随着对空间碎片、空间飞行器安全的关注及大范围海空实时监控态势感知需求的增强,有效利用在轨运载末子级及构建天基AIS/ADS-B通信系统已成为发展趋势。在此背景下,首次提出将二者结合优势互补的设想,分析了基于末子级留轨应用的AIS/ADS-B可重构通信载荷的民用及军用研究价值,比较了国内外研究现状,设计了总体方案,并对后续工作开展面临的技术难题等进行了阐述。该设想对该领域研究的深入开展具有借鉴意义。

飞矛对空间运载火箭残骸的锚固捕获特性研究

随着在轨废弃航天器的不断增多,飞矛捕获成为一种清除大型空间碎片的新式方法。首先通过分析典型废弃航天器的特征属性,选定了运载火箭末子级作为飞矛捕获的在轨演示目标。接着提出了一种一体式多层级倒刺结构的飞矛,通过飞矛撞击末子级靶板的有限元动力学仿真,研究了不同初速下飞矛的锚固效果。最后为模拟空间捕获场景,赋予了捕获目标不同的自旋速度,研究了飞矛对运动末子集靶板的锚固特性。结果表明飞矛的撞击固定末子级靶板的最佳锚固初速为70 m/s,并且在此速度下运动状态下的末子级靶板仍可被飞矛锚固捕获。可见飞矛在空间中捕获运载火箭残骸的方案是可行的,并且揭示出飞矛捕获方式对目标运动状态的不敏感性。

Microstructure and mechanical properties of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy sintered at different SPS temperatures

TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.

宋晓波 Something Cold Something Warm

内心的冷暖07年的开始,对宋晓波来说,有喜亦有忧。喜的是接到了入行的第一部戏——《青蛙王子》。演的角色很贴近他的性格,家中的末子,温柔体贴。合演的都是好男儿的自家兄弟,也许有悄悄地私下竞争,但互相之间的熟悉,缓解了因为初次演戏带来的紧张不安。上海的冬天,风冷得刺骨,整整3个月的连轴拍摄,剧组的人几乎都患过感冒发过烧,晓波也很注意御寒,常常是贴好暖宝宝再加一件外套。恶劣的天气没有困扰他,到是吻戏让他深刻体会戏不好演,"

放学快回家别急坏爸妈

每天放学后,如果父母说要接你,一定不要急着自己走,安静(jing)地呆在学校等待父母;如果家长因故不能来,在独自上学、回家时。

江泽民主席强调没有科技创新只能受制于人

中共中央总书记、国家主席江泽民看望出席全国政协九届一次会议的科学家和科技工作者,并和他们一起座谈。江主席强调,创新是一个民族进步的灵魂,是一个国家兴旺发达的不竭动力。没有科技创新,总是步人后尘,经济就只能永远受制于人。

Microstructures and properties of Al-50%SiC composites for electronic packaging applications

Al？50%SiC （volume fraction） composites containing different sizesofSiC particles （average sizesof 23, 38 and 75 μm） were prepared by powder metallurgy. The influences of SiC particle sizes and annealing on the propertiesof the compositeswere investigated. The results show that SiC particles are distributed uniformly in the Al matrix. The coarse SiC particles result in higher coefficient of thermal expansion （CTE） and higher thermal conductivity （TC）, while fine SiC particles decrease CTE and improve flexural strength of the composites. The morphology and size of SiC particles in the composite are not influenced by the annealing treatment at 400℃for 6h. However, the CTE and the flexural strength of annealed composites are decreased slightly, and the TCis improved. The TC, CTE and flexural strength of the Al/SiC composite with averageSiC particlesize of75 μm are 156 W/（m·K）, 11.6×10^-6K^-1 and 229 MPa, respectively.

Microstructure and fracture toughness of a TiAl-Nb composite consolidated by spark plasma sintering

A TiAl-Nb composite was prepared by spark plasma sintering （SPS） at 1250 °C and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9：1 for improving the fracture toughness of TiAl alloy at room temperature. The microstructure, phase constitute, fracture surface and fracture toughness were determined by X-ray diffractometry, electron probe micro-analysis, scanning and transmission electron microscopy and mechanical testing. The results show that the sintered samples mainly consist of γ phase, O phase, niobium solid solution （Nbss） phase and B2 phase. The fracture toughness is as high as 28.7 MPa？m1/2 at room temperature. The ductile Nbss phase plays an important role in absorbing the fracture energy in front of the cracks. Moreover, B2 phase can branch the propagation of the cracks. The microhardness of each phase of the composite was also tested.

Vascular endothelial growth factor attenuates hepatic sinusoidal capillarization in thioacetamide-induced cirrhotic rats

AIM: To investigate the effect of vascular endothelial growth factor (VEGF) transfection on hepatic sinusoidal capillarization. METHODS: Enhanced green fluorescent protein (EGFP)/ VEGF transfection was confirmed by immunofluorescence microscopy and immunohistoche-mistry both in primary hepatocytes and in normal liver. Cirrhotic rats were generated by thioacetamide (TAA) administration and then divided into a treatment group, which received injections of 400 μg of plasmid DNA encoding an EGFP- VEGF fusion protein, and a blank group, which received an equal amount of normal saline through the portal vein. The portal vein pressure was measured in the normal and cirrhotic state, in treated and blank groups. The average number of fenestrae per hepatic sinusoid was determined using transmission electron microscopy (TEM), while the relative abundance of VEGF transcripts was examined by Gene array. RESULTS: Green fluorescent protein was observed in the cytoplasms of liver cells under immunofluorescence microscopy 24 h after transfection with EGFP/VEGF plasmid in vitro. Staining with polyclonal antibodies against VEGF illustrated that hepatocytes expressedimmunodetectable VEGF both in vitro and in vitro. There were significant differences in the number of fenestrae and portal vein pressures between normal and cirrhotic rats (7.40 ± 1.71 vs 2.30 ± 1.16 and 9.32 ± 0.85 cmH2O vs 17.92 ± 0.90 cmH2O, P < 0.01), between cirrhotic and treated rats (2.30 ± 1.16 cmH2O vs 4.60 ± 1.65 and 17.92 ± 0.90 cmH2O vs 15.52 ± 0.93 cmH2O, P < 0.05) and between the treatment group and the blank group (4.60 ± 1.65 cmH2O vs 2.10 ± 1.10 cmH2O and 15.52 ± 0.93 cmH2O vs 17.26 ± 1.80 cmH2O, P < 0.05). Gene- array analysis revealed that the relative abundance of transcripts of VEGF family members decreased in the cirrhotic state and increased after transfection. CONCLUSION: Injection of a plasmid encoding VEGF through the portal vein is an effective method to induce the formation of fenestrae and decrease portal vein pressure in cirrhotic rats. Therefore, it may be a good choice for treating hepatic cirrhosis and portal hypertension.

Theoretical and experimental investigation of Ti alloy powder production using low-power plasma torches

This study was carried out to investigate the possibility of titanium alloy metal powder production using low-power plasma torches.An argon DC non-transferred arc plasma torch was designed,and numerical analysis was conducted to determine the plasma jet properties and wire temperature.The highest velocities inside the nozzle attachment were between 838 and 1178 m/s.The velocities of the jets at the apex were between 494 and 645 m/s for different gas flow rates.The studied plasma gas flow rates had no significant effect on the effective plasma jet length.It was shown that the plasma jet length can be estimated by numerical analysis using the temperature and velocity changes of the plasma jet over distance.It was observed that the powders produced were spherical without any satellites.As a result of this study,a plasma torch was developed and powder production was performed successfully by using relatively low torch power.

Molecular control of memory in nematode Caenorhabditis elegans

Model invertebrate organism Caenorhabditis elegans has become an ideal model to unravel the complex processes of memory. C. elegans has three simple forms of memory： memory for thermosensation, memory for chemosensation, and memory for mechanosensation. In the form of memory for mechanosensation, short-term memory, intermediate-term memory, and long-term memory have been extensively studied. The short-term memory and intermediate-term memory may occur in the presynaptic sensory neurons, whereas the long-term memory may occur in the postsynaptic interneurons. This review will discuss the recent progress on genetic and molecular regulation of memory in C. elegans.

Development of a pentaethylenehexamine-modified solid support adsorbent for CO_2 capture from model flue gas

A novel solid support adsorbent for CO2capture was developed by loading pentaethylenehexamine(PEHA)on commercially available mesoporous molecular sieve MCM-41 using wet impregnation method.MCM-41 samples before and after PEHA loading were characterized by X-ray powder diffraction,N2adsorption/desorption,thermal gravimetric analysis and scanning electron microscope to investigate the textural and thermo-physical properties.CO2adsorption performance was evaluated in a fixed bed adsorption system.Results indicated that the structure of MCM-41 was preserved after loading PEHA.Surface area and total pore volume of PEHA loaded MCM-41 decreased with the increase of loading.The working adsorption capacity of CO2could be significantly improved at 60%of PEHA loading and 75°C.The effect of the height of adsorbent bed was investigated and the best working adsorption capacity for MCM-41-PEHA-60 reached 165 mg·(g adsorbent)-1at 75°C.Adsorption/desorption circle showed that the CO2working adsorption capacity of MCM-41-PEHA kept stable.

A Methodology for Producing Uniform Distribution of UO2 in a Tungsten Matrix

We report a method to produce a uniform mixture of uranium dioxide spherical particles in a tungsten matrix. This method involves mixing 0.5 weight percent of high density polyethylene binder with 60 volume percent uranium dioxide spheres and 40 volume percent tungsten powders. Initially, hafnium oxide spheres were used as a surrogate for uranium dioxide spheres. The HfO2/W/PE powders were thoroughly mixed in a Turbula, then mixed on a hot plate above the drop point of the binder. These powders were then densified using spark plasma sintering. Microstructure was evaluated using scanning electron microscopy, density was measured and hardness measurements were made. Initial carbon content of the powders were measured and carbon content of the sintered materials was measured. Subsequently, W/UO2/Binder powders were mixed using the same methodology to ensure the process could be used for this system. These powders were sintered using hot isostatic pressing and microstructures evaluated. The resultant microstructures contained uniform distribution of HfO2 and UO2 particles in the tungsten matrix with very low carbon content.

Fabrication and Mechanical Properties of 2024 Aluminum Alloy Reinforced by FeNiCrCoAl_3 High Entropy Particles

This article mainly discussed bulk material lHvl^ared by powder metallurgy, and the commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy powder （both produced by argon gas atomization process） were ball-milled for different hours. The prepared powder was consolidated by hot extrusion method. The microstruetures of the milled powder and bulk alloy were examined by X - Ray Diffraction （XRD）, Scanning Electron Microscopy （SEM） and Transmission Electron Microscopy （TEM）. The thermal stability was tested by differential scanning calorimetry （DSC）. Mechanical properties of the extruded alloy were examined by Vickers hardness tester and mechanical testing machine. The results show that after milling, the mixed particle sizes and microstructures of the alloy powder change obviously. The compressive strength of the extruded alloy has reached 580 MPa under certain conditions of milling time and composition.

Microstructure and compressive deformation of hypereutectic Al-Si-Fe based P/M alloys fabricated by spark plasma sintering

Al-Si-Fe based alloys are attractive light-weight structural materials for automotive engine components because of their high wear resistance, low density and low thermal expansion. Al-17Si 5Fe-2Cu-lMg-lNi-lZr alloys were produced in compact form by a spark plasma sintering （SPS） technique using gas atomized powders. The mean grain size of the compact was 530 nm, and fine equiaxed grains and uniformly distributed precipitates were observed in the compact. The compressive deformation behavior of the SPSed materials was examined at various temperatures and strain rates. All the true stress-true strain curves showed steady state flow after reaching peak stress. The peak stress decreased with increasing test temperature and decreasing strain rate. In the deformed specimens, the equiaxed grain morphology and the dislocation microstructure within the equiaxed grains were observed. These facts strongly indicated the occurrence of dynamic recrystallization during high temperature deformation of the present alloy.