Orbit determination and prediction of GEO satellite of BeiDou during repositioning maneuver

In order to establish a continuous GEO satellite orbit during repositioning maneuvers, a suitable maneuver force model has been established associated with an optimal orbit determination method and strategy. A continuous increasing acceleration is established by constructing a constant force that is equivalent to the pulse force, with the mass of the satellite decreasing throughout maneuver. This acceleration can be added to other accelerations, such as solar radiation, to obtain the continuous acceleration of the satellite. The orbit determination method and strategy are illuminated, with subsequent assessment of the orbit being determined and predicted accordingly. The orbit of the GEO satellite during repositioning maneuver can be determined and predicted by using C-Band pseudo-range observations of the BeiDou GEO satellite with COSPAR ID 2010-001A in 2011 and 2012. The results indicate that observations before maneuver do affect orbit determination and prediction, and should therefore be selected appropriately. A more precise orbit and prediction can be obtained compared to common short arc methods when observations starting 1 day prior the maneuver and 2 h after the maneuver are adopted in POD (Precise Orbit Determination). The achieved URE (User Range Error) under non-consideration of satellite clock errors is better than 2 m within the first 2 h after maneuver, and less than 3 m for further 2 h of orbit prediction.     

Characterization of ionospheric amplitude scintillations using wavelet entropy detrended GNSS data

The extensive monitoring networks of Global Navigation Satellite System (GNSS) ionospheric scintillation have been established to continuously log observation data. Further, the amplitude scintillation index and the phase scintillation index, which are derived from scintillation observations, are anticipated to accommodate the accuracy requirement of both the user level and the monitoring station level. However, raw scintillation observations essentially measure superposed waveform impairments of GNSS signals propagating through ionosphere and troposphere. It implies that fluctuations of raw scintillation observations are caused by multiple factors from the entire radio propagation environment. Hence, it is crucial to characterize ionospheric scintillations from GNSS observation data. And the characterization is implemented through extracting fluctuations of raw observations merely induced by ionospheric scintillations. Designed to address this problem by means of Fourier filtering detrending, the present work investigates the influence of varying detrending cutoff frequencies on wavelet statistical energy and wavelet entropy distributions of scintillation data. It consequently derives criteria on the optimum detrending cutoff frequency for three types of raw amplitude scintillation data, which are classified by their wavelet energy distributions. Results of the present work verify that detrending with specific optimum cutoff frequencies rather than the fixed and universally applicable one renders the validity and credibility of characterizing ionospheric scintillations as the part of GNSS observation fluctuations purely induced by ionosphere electron density irregularities whose scale sizes are comparable with or smaller than the Fresnel scale.     

含能材料低温松驰WLF方程的两种求值法

通过玻璃化转变温度和表同活化能以及由ＶＦＴ方程导得ＷＬＦ方程粘弹系数的两种新方法,用该方法分别计算１０个体系的粘弹系数,结果表明,用ＤＳＣ技术可以获得ＷＬＦ方程,３种计算方法获得的粘弹系数符合较好。     

大型星载可展开天线的展开动力学问题

针对大型星载可展开天线所具有的尺寸大、刚性小、展开机构复杂,所处环境恶劣等特点,结合天线的构形特征,着重从可展开天线展开动力学的建模角度,综述了可展开天线的展开动力学问题。对解决途径及办法提出了一些看法。     

氢在超音速气流中的燃烧过程

氢燃料超音速燃烧冲压发动机(简称超燃冲压)为主体的吸气式组合动力装置,已被证明是空天飞机推进器的最佳方案[1]。因而研究氢在超音速气流中的燃烧过程是一个重要的课题。国外近年来进行了大量的有关理论与实验研究工作[2、3],但大多数的研究停留在氢处于静止与等压状态下的反应过程。在超燃燃烧室中的实际燃烧过程,由于不同的燃烧室进口气流状态,大体有以下三种基本类型:扩散型燃烧、扩散动力型燃烧、动力型燃烧。      

关于低RCS目标外形优化中目标函数的确定

在分析了低RCS目标外形优化中现有的两种目标函数的局限性的基础上,根据雷达检测概率与目标RCS分布之间的关系,提出了一种新的目标函数,即目标在威胁区域内其RCS大于规定的临界RCS的概率。算例表明本文所提出的目标函数比现有的目标函数更为有效,适用范围更广。为低RCS目标外形优化设计以及气动与隐身一体化设计提供了一个合理而有效的目标函数。     

某型飞机断裂谱的低载截除

研究了截除低载对全机结构各部位裂纹扩展寿命的影响,导出寿命误差与裂纹扩展比的关系,并指出寿命误差主要取决于开裂结构的材料参数,而开裂部位的影响则可忽略不计。     

一种多晶石墨的拉伸蠕变行为

对一种多晶石墨材料进行了拉伸蠕变试验后,用ＲＡＭＡＮＯＲＵ１０００拉曼光谱仪对蠕变前后的试样作了分析,并用扫描电镜观察了蠕变前后试样纵向剖面的孔隙变化。结果表明：在１７００℃,０．７ＭＰａ的应力作用下多晶石墨材料不发生明显蠕变。蠕变初期可用ε－ε０＝Ａｔｎ进行描述,在不同温度和应力下ｎ值从０．４８５～０．８之间变化。在同一应力条件下,随温度提高,ｎ值增大。激光拉曼光谱仪和扫描电镜分析表明,多晶石墨蠕变后石墨化程度增加、孔隙增多、变大。     

型号研制的矩阵管理与两师系统

讨论了卫星型号研制中组织机构体制的深化改革问题;介绍了多型号通常采用的矩阵管理体制;论述了两师系统在矩阵管理中的作用;提出了加强两师系统的措施。     

Al-4.5％Cu合金的过冷及凝固组织特征

对Ａｌ－４．５％Ｃｕ合金在纯石黑坩埚中用卤盐熔剂净化后的过冷度及其在金属锭模中的凝固组织特征进行了研究。实验结果发现：粘度较大的半固态熔剂对合金的净化作用较强,可使合金在金属锭模中得到６２℃的形核过冷度;金属熔体净化得到的热力学过冷度对合金形核及最终宏观组织的影响明显不同于激冷得到的动力学过冷度对其所产生的影响,在一定过冷度下,晶粒尺寸随热力学过冷度的增大而增大