低轨天基信息定向分发区域分割编码控制方法

为提高低轨指向性信息分发链路的频谱利用效率，从天基分发平台与地面用户的相对位置关系入手，建立了分发指向、编码增益与信道传输容量的量化关系。在此基础上，提出一种低轨天基信息定向分发区域分割编码控制方法，该方法针对不同信息分发区域，采用最小均方误差(MMSE)作为区域分割准则选择编码方式，既提升了信道传输效率也便于工程实现。最后，本文通过仿真分析了方法的效能和性能影响因素，并与现有自适应编码方法进行了对比，验证了本方法的有效性和可靠性。     

An empirical solar radiation pressure model for satellites moving in the orbit-normal mode

We present a family of empirical solar radiation pressure (SRP) models suited for satellites orbiting the Earth in the orbit normal (ON) mode. The proposed ECOM-TB model describes the SRP accelerations in the so-called terminator coordinate system. The choice of the coordinate system and the SRP parametrization is based on theoretical assumptions and on simulation results with a QZS-1-like box-wing model, where the SRP accelerations acting on the solar panels and on the box are assessed separately. The new SRP model takes into account that in ON-mode the incident angle of the solar radiation on the solar panels is not constant like in the yaw-steering (YS) attitude mode. It depends on the elevation angle of the Sun above the satellite’s orbital plane. The resulting SRP vector acts, therefore, not only in the Sun-satellite direction, but has also a component normal to it. Both components are changing as a function of the incident angle. ECOM-TB has been used for precise orbit determination (POD) for QZS-1 and BeiDou2 (BDS2) satellites in medium (MEO) and inclined geosynchronous Earth orbits (IGSO) based on IGS MGEX data from 2014 and 2015. The resulting orbits have been validated with SLR, long-arc orbit fits, orbit misclosures, and by the satellite clock corrections based on the orbits. The validation results confirm that—compared to ECOM2—ECOM-TB significantly (factor 3–4) improves the POD of QZS-1 in ON-mode for orbits with different arc lengths (one, three, and five days). Moderate orbit improvements are achieved for BDS2 MEO satellites—especially if ECOM-TB is supported by pseudo-stochastic pulses (the model is then called ECOM-TBP). For BDS2 IGSOs, ECOM-TB with its 9 SRP parameters appears to be over-parameterized. For use with BDS2 IGSO spacecraft we therefore developed a minimized model version called ECOM-TBMP, which is based on the same axis decomposition as ECOM-TB, but has only 2 SRP parameters and is supported by pseudo-stochastic parameters, as well. This model shows a similar performance as ECOM-TB with short arcs, but an improved performance with (3-day) long-arcs. The new SRP models have been activated in CODE’s IGS MGEX solution in Summer 2018. Like the other ECOM models the ECOM-TB derivatives might be used together with an a priori model.     

北斗空间信号误差统计特征及描述方法研究

通过对比北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)广播星历与事后精密星历,提取了轨道和卫星时钟误差。基于北斗轨道误差及北斗卫星时钟误差统计特征分析,构建区别于全球定位系统(Global Positioning System,GPS)的BDS空间信号用户测距误差(Signal-In-Space User Range Error,SISRE)描述方法,对BDS广播星历中用户测距精度(User Range Accuracy,URA)进行了验证。6个月的北斗数据测试结果表明,北斗GEO、IGSO和MEO卫星的URA分别为3.0m、1.9m和1.6m。     

《思想道德修养与法律基础》课多媒体教学设计的探索

《思想道德修养与法律基础》课多媒体教学设计要坚持教材体系向教学体系转化等原则,将书本内容形象化,抽象理论直观化;基本知识情景化,教学环境轻松化;媒体素材选择化,各种资源主题化;学习空间无限化,学习方式交互化。从而使现代教育思想、多媒体技术和传统教学模式有机地结合起来,通过教学资源平台和网络平台等多媒体技术,创设利于教学的学习环境,完成对道德与法律知识的建构和对学生行为的指导。     

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.     

基于激光反射层析法的换能器声场测量技术及仿真研究

换能器的辐射声场分布能够直接反映出换能器声学性能的好坏，若不能精确测量出换能器的辐射声场，则会对换能器的诊断和评估造成严重影响。从理论仿真的角度出发，推导了运用激光反射层析法重建换能器辐射声场的理论公式，着重利用推导出的理论公式对激光反射层析法进行了仿真计算。结果表明激光反射层析法能够精确地重建出换能器的辐射声场分布及声场中的声压量值，这为换能器的声场重建及声压测量提供了一种可行的方法。     

Spatial transformation of general sampling-aliasing frequency region for rotating-blade parameter identification with emphasis on single-probe blade tip-timing measurement

Blade-health monitoring is intensely required for turbomachinery because of the high failure risk of rotating blades. Blade-Tip Timing (BTT) is considered as the most promising technique for operational blade-vibration monitoring, which obtains the parameters that characterize the blade condition from recorded signals. However, its application is hindered by severe undersampling and stringent probe layouts. An inappropriate probe layout can make most of the existing methods invalid or inaccurate. Additionally, a general conflict arises between the allowed and required layouts because of arrangement restrictions. For the sake of economy and safety, parameter identification based on fewer probes has been preferred by users. In this work, a spatial-transformation-based method for parameter identification is proposed based on a single-probe BTT measurement. To present the general Sampling-Aliasing Frequency (SAFE) map definition, the traditional time–frequency analysis methods are extended to a time-sampling frequency. Then, a SAFE map is projected onto a parameter space using spatial transformation to extract the slope and intercept parameters, which can be physically interpreted as an engine order and a natural frequency using coordinate transformation. Finally, the effectiveness and robustness of the proposed method are verified by simulations and experiments under uniformly and nonuniformly variable speed conditions.     

四度时空坐标变换的图像及其应用

对四度时空坐标的几何图像给以量化的描述,将洛伦兹变换与坐标的旋转对应起来。并利用此图像中不变量对坐标的投影说明不同惯性参照系之间所表现出的相对论时空特性。     

空间坐标转换技术的分析与研究(一)

系统分析了空间坐标转换的不同形式及其相互关系,运用旋转矩阵理论作了较为深入的探讨,指出了使用中应注意的问题。提出了齐次矩阵,微分算子及雅可比阵矩等有用概念,作为例子,讨论了这些概念在机器人学中的应用。     

用两颗GPS卫星确定低轨卫星轨道的初值方法

研究了用两颗全球定位系统（ＧＰＳ）卫星粗略确定低轨卫星轨道的问题,并着重讨论了其中的初值问题,给出了一种有效的初值方法。实验结果证明：这种方法能给出一个确定的、实用的初值,大大减少了初轨计算的计算量,并使得算法收敛更加有保障。在工程实用方面比传统的猜测方法具有较大的优势。