PICA-X的制备及其炭化前后性能研究

采用不同浓度热塑性酚醛树脂溶液浸渍莫来石纤维毡,经过溶胶-凝胶反应和常压干燥后,制备出酚醛浸渍陶瓷烧蚀体(PICA-X,0.45~0.50 g/cm~3),后研究了其炭化前后微观形貌、力学、隔热及抗氧化性能。结果表明:PICA-X具有莫来石纤维增强酚醛气凝胶复合结构,其弯曲强度为26.7~34.0 MPa,热导率为36~40 m W/(m·K)。经过1 000℃炭化后,C-PICA-X的弯曲强度为13.9~14.5 MPa,热导率为41~45m W/(m·K);PICA-X炭化前后均表现出较好的抗氧化性能。     

粒子侵蚀模型及粒子侵蚀下绝热材料烧蚀数值计算

从粒子动力学参数出发,分析了粒子与炭化层相互作用机制,导出计算粒子对炭化层作用力,再根据强度理论,推导出粒子对炭化层的侵蚀模型。应用该模型,对实验发动机中粒子侵蚀下的绝热材料烧蚀进行了数值计算,计算中采用了燃气流动与烧蚀耦合计算方法,计算结果与实验结果基本一致,表明所建立的粒子侵蚀可用于固体火箭发动机中粒子侵蚀下绝热材料烧蚀的预估。     

周期性变速扫描机构驱动控制方法研究

针对存在周期性变速运动的微波遥感器机械扫描驱动系统，根据其扫描运动的速度、位置控制要求，采用步进电机做为执行元件研制开发了一套驱动控制系统。该系统不仅能完成运动轨迹的控制，而且速度精度和扫描周期的误差等指标满足给定的要求。描述了该系统的组成，转速、转矩等参数的特性匹配设计过程以及控制实现方法，并对系统的速度精度、扫描周期误差等主要性能测试进行了简单介绍。     

有机阻燃剂对UPR包覆材料耐烧蚀性能的影响及分析

选取有机磷系阻燃剂A、氮系阻燃剂B和三聚氰胺C、卤系阻燃荆十溴联苯醚D,利用田口方法的望小特征系统研究了有机阻燃剂对UPR包覆材料耐烧蚀性能的影响,得到最佳配比为A:B:C:D=8:24:24:24,其中阻燃剂D对UPR线烧蚀率的影响最为显著.通过对烧蚀成炭层进行形貌分析,探讨了有机阻燃剂改性UPR包覆层的耐烧蚀特征;并结合阻燃剂/UPR复合材料的TG-DTG分析,探索了不同阻燃荆对改性UPR包覆材料耐烧蚀性能的作用机理.结果表明,磷系阻燃剂能促进UPR材料成炭,氮系阻燃剂通过气化作用保护UPR基体,卤系阻燃剂具有一定的气相阻燃和固相促进成炭作用.     

Reloading partly recovers bone mineral density and mechanical properties in hind limb unloaded rats

Skeletal unloading results in decreased bone formation and bone mass. During long-term space flight, the decreased bone mass is impossible to fully recover. Therefore, it is necessary to develop the effective countermeasures to prevent spaceflight-induced bone loss. Hindlimb Unloading (HLU) simulates effects of weightlessness and is utilized extensively to examine the response of musculoskeletal systems to certain aspects of space flight. The purpose of this study is to investigate the effects of a 4-week HLU in rats and subsequent reloading on the bone mineral density (BMD) and mechanical properties of load-bearing bones.     

高过载条件下固体火箭发动机绝热层失效研究

根据化学反应／两相流耦合,建立了铝粒子燃烧模型,通过化学反应速率模型的模化湍流燃烧,对含铝推进剂固体火箭发动机在高过载条件下的内流场进行数值研究。结果表明,过载条件下燃烧室局部异常铝滴积聚及剧烈的化学放热反应是导致绝热层异常烧蚀的主要原因。     

Microstructural evolution and mechanical properties of brazed IN718 ultrathin-walled capillary structure using different particulate reinforced filler alloy

The development of hypersonic precooled combined cycle engine provides a reliable power system for the future intercontinental navigation and reusable space orbital transportation.The compact heat exchanger precooler is the key component of the cooling cycle system, which provides efficient heat management for the hypersonic engine. This investigation mainly focused on the manufacturing process of precooler, and the typical structure of the precooler, ultrathin-walled capillary structure, was fa...     

星载可展开天线波束指向测试方法研究

综合天线方向图测量和光学测量方法研究了天线远场测量和近场测量光学测试系统, 进而利用光学仪器测试了星载天线波束指向的两种测试方法. 望远镜结合天线远场测试系统能较准确地测试出天线波束指向. 同时, 提出了采用准直仪及波罗棱镜在天线平面近场测试系统测试波束指向的方法. 海洋二号卫星载荷校正辐射计观测天线波束指向的测试表明, 该方法是有效性和准确性的, 其可以推广至一般高增益天线测试.      

原子氧对航天材料的影响与防护

文章综述了低地球轨道（LEO）中原子氧（AO）环境对航天材料影响的研究现状。首先介绍AO对材料的危害及作用机制等。然后重点阐述了国内外学者关于AO与Al、Ag、Cu、Ni等金属材料以及半导体材料作用的研究成果。最后总结了AO的防护方法,及其对不同材料抗AO侵蚀能力的改善结果。     

空间原子氧对低地球轨道航天器用粘结剂的腐蚀效应影响

原子氧是低地球轨道(leo)-种重要的空间环境因素,地面模拟试验是用于开展leo航天器备选材料原子氧环境评价的主要手段.利用北京卫星环境研究所的原子氧设备,对牌号为e-32的环氧树脂和牌号为gs414的硅橡胶两种粘结剂进行了评价试验.依据轨道参数与航天器两年的设计寿命,选定试验中原子氧的等效积分通量为1.4×1021atom/cm2.试验结果表明,环氧树脂样品出现了较大的质量损失,而硅橡胶样品的质量损失则相对较小.根据质量损失计算环氧树脂样品的原子氧反应率处于3.2×10-24～3.8×10-24cm3/atom之间.试验后的环氧树脂样品表面颜色变浅,硅橡胶样品的表面则呈现了玻璃化.对两种材料都进行了表面形貌分析,试验前后测试结果的对比分析表明原子氧的氧化作用使材料表面发生了较大的变化. abstract： atomic oxygen (ao) is prevalent in low earth orbit (leo). ground-based testing on ao exposure was performed to investigate the effects of atomic oxygen on materials to be used in leo spacecraft. two types of adhesive materials, e-32 epoxy and gs414 silicone, were tested in the atomic oxygen testing facility at beijing institute of spacecraft environment engineering (bisee). the equivalent atomic oxygen fluence in test was approximately 1.4×1021 atom/cm2 as determined based on two years' exposure on leo. significant mass losses of the epoxy adhesive samples were observed after the exposure to atomic oxygen, but relatively small mass changes were found in the silicone samples. the erosion yields of epoxy samples range from 3.2×10-24 cm3/atom to 3.8×10-24 cm3/atom. bleaching by atomic oxygen was found in the epoxy samples. the surface on the silicone sample was glossed after ao exposure. the external appearance of both kinds of materials was analyzed using scanning electron microscope (sem) and x-ray photoelectron spectroscopy (xps). a comparison between unexposed and exposed samples shows noticeable changes on the s