军事星中的铷和石英频率标准的性能数据——在模拟太空环境中地检和实际轨道中所得数据的比较

航天计划中将增加原子频标的使用,以获得精确的时间和稳定的频率。GPS系统所具有的卓越的导航功能主要是由系统中采用的原子频标带来的。新一代的军事通信卫星(Milstar)载有多路复合铷原子频标以满足各种通讯和操作上的需要。第一颗军用通讯卫星,DFS-1使用了复合多路石英晶体振荡器,第二颗军用通讯卫星,1995年发射的DFS-2,是第一颗使用铷原子频标的军用通讯卫星。这以后发射的卫星都使用了铷原子频标。     

光学加工射频离子源的去除函数与稳定性研究

在研究了射频离子源的结构、工作原理和性能的基础上,进行了光学镜面抛光离子束的去除效率与稳定性测试。实验结果表明射频离子源去除函数的形状为回转高斯形,利用Φ15mm的栅网,在靶距为30mm、离子能量900eV时,去除函数的峰值去除率为194nm/min,体积去除率为19.2×10-3mm3/min,半峰全宽值为9.2mm;并且去除函数的峰值去除率与体积去除率的变化均在3%以内,半峰全宽值的变化在1.7%以内。因此,射频离子源具有光学镜面抛光加工所需的去除效率,而且射频离子源具有好的稳定性,具备光学加工的潜能。     

Navigation sensors and systems in GNSS degraded and denied environments

Position, velocity, and timing(PVT) signals from the Global Positioning System(GPS)are used throughout the world but the availability and reliability of these signals in all environments has become a subject of concern for both civilian and military applications. This presentation summarizes recent advances in navigation sensor technology, including GPS, inertial, and other navigation aids that address these concerns. Also addressed are developments in sensor integration technology with several examples described, including the Bluefin-21 system mechanization.     

倾转旋翼机设计特点及难点浅析

通过对国外倾转旋翼机的发展历程及具有代表性的V-22"鱼鹰"设计特点进行分析,总结了倾转旋翼类飞机的设计特点及技术难点,并对倾转旋翼机的发展前景进行了展望,为国内此类飞机的研制提供思路和参考。     

离子束加工中工件吸收热功率分析与建模研究

利用束流修正理论和蒙特卡罗模拟法对离子束加工中某一工艺参数下工件吸收的功率进行理论建模,然后采用测温实验对理论模型进行验证.设计实验时,利用有限元仿真确定了一种合理的轰击靶材铜,简化了实验并且方便了计算.     

设计测取精度信息的导弹飞行试验计划用的统计方法

决定导弹飞行试验计划测得精度能力的因素有:被试系统(即惯性制导系统、天文导航系统等)的误差模型;测量系统(即外测系统、遥测等)的误差模型;数据精度;飞行试验前得到的先验信息;弹道(或轨道)以及数据分析的方法。这些因素可以用数字计算机进行仿真,并且可以借助加权最小二乘回归法对具体的精度值求得定量的统计指标。在设计试验计划阶段,数字仿真和统计分析可用来进行综合研究,以便使弹道、测量系统和飞行前试验计划要求等试验条件达到最佳。通过正确的试验设计,常常可以把飞行试验计划测量精度的能力提高10-100倍。     

方腔流致振荡及噪声的数值研究

采用直接数值模拟方法,研究了低Reynolds数下L/D=2的方腔亚声速流致振荡现象及其诱导的噪声。结果表明,在所计算的参数范围内,振荡都是由Rossiter II模态主导;来流边界层变薄会导致低频成分的出现,其产生的直接原因是涡与后拐角撞击方式的切换,根源在于回流区与剪切层相互作用形式的不稳定。采用本征正交分解(POD)方法,分析了不同振荡形式所对应的本征模态涡结构及其与后拐角撞击方式的关系。计算得到并分析了声波的产生和传播过程,结果与已有实验结果和理论模型符合良好。     

Science Missions Using CubeSats

As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems, such as resource management, environmental problems, and disaster management, as well as space science questions, thanks to their lower cost and faster development process CubeSats can benefit humanity and therefore, young scientists and engineers have been motivated to research and develop new CubeSat missions. Not very long after their inception, CubeSats have evolved to become accepted platforms for scientific and commercial applications. The last couple of years showed that they are a feasible tool for conducting scientific experiments, not only in the Earth orbit but also in the interplanetary space. For many countries, a CubeSat mission could prompt the community and young teams around the world to build the national capacity to launch and operate national space missions. This paper presents an overview of the key scientific and engineering gateways opened up to the younger scientific community by the advent and adaptation of new technology into CubeSat missions. The role of cooperation and the opportunities for capacity-building and education are also explored. Thus, the present article also aims to provide useful recommendations to scientists, early-career researchers, engineers, students, and anyone who intends to explore the potential and opportunities offered by CubeSats and CubeSats-based missions.      

航天飞机指控中心Unix工作站中专家系统的实时数据获取

最具代表性的美国技术杰作之一可能是位于德克萨斯州休斯顿的约翰逊航天中心的航天指挥控制中心(MCC)。该中心各指挥室经历了美国技术史上许多重大事件,如首次登月、营救天空实验室以及首次发射航天飞机。60年代初MCC首次启用时,的确是技术杰作。然而该设施自阿波罗任务后只进行过不大的改进。直到最近,它仍然维持着以单主机的结构,