双太阳翼GEO卫星在轨角动量管控方法

地球同步轨道(GEO)卫星在轨的主要环境干扰力矩为太阳光压力矩和重力梯度力矩,干扰力矩的累积效应表现为飞轮转速的变化,需要通过外力矩进行角动量卸载避免飞轮饱和。由于GEO磁场极弱,卫星无法使用磁力矩卸载,只能通过喷气卸载,而喷气将对卫星轨道产生影响,因此需要尽可能延长卸载周期。针对配置双对称太阳电池阵GEO卫星的角动量管控需求,首先建立卫星在惯性空间中角动量积累模型,并映射到卫星本体系中,得到本体系中的角动量变化规律。通过飞轮在轨转速遥测数据,精确辨识获取环境干扰力矩特征参数,获得真实可靠的干扰模型。以角动量卸载周期最长为原则,基于在轨环境干扰模型制定角动量管控策略,并准确预估下次角动量卸载时间。经在轨数据处理与分析表明:提出的角动量管控策略,可有效将飞轮的角动量卸载周期提升为原来的2倍,有效提升卫星在轨应用效能,具有实际工程意义。     

基于距离像特征的复合速度估计算法研究

首先分析了步进频率宽带信号混频处理原理和目标速度对距离像的影响。在此基础上,提出了基于距离像熵和距离像对比度的速度估计算法,详细分析了这两种算法的数学原理、步骤、效果、适用条件等。最后,基于这两种算法又提出了复合速度估计算法,大大提高了速度估计精度。     

首颗自主地月转移微卫星“龙江二号”

本文对世界首颗独立完成地月转移、近月制动、环月飞行的微卫星“龙江二号”进行了介绍。首先阐述了龙江二号的任务目标和总体方案;然后重点分析了轨道设计与控制、复杂电磁干扰的标定与抑制、宽视场三维基线干涉测量等关键技术难点;接着回顾了任务的实施过程;最后详细介绍了低频射电探测仪、沙特光学相机和VHF/UHF通信模块与学生微型CMOS相机等有效载荷,并展示了上述载荷获取的初步成果。     

一种针对局部结构的有限元模型修正方法

针对实际结构有限元模型（FEM）的建模误差通常仅存在于局部区域,提出了一种对局部结构单独进行模型修正的方法。首先,根据频响函数（FRF）解耦理论得到由残余结构频响函数与包含待修正参数的局部结构动刚度所重构的整体结构频响函数的拟合值,然后通过迭代优化使其与测量值的残差最小化,从而得到参数的极大似然估计。在此基础上,将残差关于参数的灵敏度以局部结构动力学矩阵表示,建立了模型修正的基本方程,利用整体结构的测试数据即可直接对分离出来的局部结构进行模型修正。最后,对喷气式飞机和三角机翼飞机分别进行了数值模拟和实验研究,验证了所提方法的可行性和有效性。结果表明,所提方法可以成功地用于仅局部区域含有建模误差的实际结构有限元模型的修正,修正后的有限元模型的动态特性与实际结构有较好的一致性。     

高超声速滑翔目标自适应跟踪方法

针对机动模式复杂多变的高超声速滑翔目标跟踪问题,提出了一种机动频率自适应跟踪方法。采用介于常速度和常加速度模型之间的Singer模型来表征目标气动力加速度的变化,从而建立跟踪系统的状态方程。根据地基雷达量测量获得系统的量测方程,鉴于距离和角度信息的量级相差较大将其由球形量测量转换为位置量测量。为了适应高超声速滑翔目标灵活多样的机动模式,基于正交性原理和无迹卡尔曼滤波算法实现了Singer模型中机动频率参数的自适应。利用滤波信息计算得到能够反映状态模型误差大小的调整因子,用于放大Singer模型中的机动频率,进而调整状态方程的过程噪声以降低模型误差。通过对2种典型机动轨迹的跟踪仿真,并与交互式多模型等方法进行比较,结果表明所提方法的跟踪精度高、计算量小,能够较好地适应阶跃机动和连续幅值变化的机动。     

Using the radial basis function neural network to predict ionospheric critical frequency of F2 layer over Wuhan

Neural networks (NNs) have been applied to ionospheric predictions recently. This paper uses radial basis function neural network (RBF-NN) to forecast hourly values of the ionospheric F₂ layer critical frequency(f_oF₂), over Wuhan (30.5N, 114.3E), China. The false nearest neighbor method is used to determine the embedding dimension, and the principal component analysis (PCA) is used to reduce noise and dimension. The whole study is based on a sample of about 26,000 observations of f_oF₂ with 1-h time resolution, derived during the period from January 1981 to December 1983. The performance of RBF-NN is estimated by calculating the normalized root-mean-squared (NRMSE) error, and its results show that short-term predictions of f_oF₂ are improved.     

我国BPL时号的频率控制系统及结果分析

根据我国现行ＢＰＬ时号的频率控制系统,分析ＴＢＰＬ时号频率控制系统的缺陷,对目前ＢＰＬ时号的频率稳定性进行了评价,提出了一种新的频率控制方案。     

Ionospheric scintillations at Guilin detected by GPS ground-based and radio occultation observations

The occurrence of ionospheric scintillations with S4 ? 0.2 was studied using GPS measurements at Guilin, China (25.29°N, 110.33°E; geomagnetic: 15.04°N, 181.98°E), a station located near the northern crest of the equatorial anomaly. The results are presented for data collected from January 2009 to March 2010. The results show that nighttime amplitude scintillations only took place in February and March of the considered years, while daytime amplitude scintillations occurred in August and December of 2009. Nighttime amplitude scintillations, observed in the south of Guilin, always occurred with phase scintillations, TEC (Total Electron Content) depletions, and ROT (Rate Of change of TEC) fluctuations. However, TEC depletions and ROT fluctuations were weak during daytime amplitude scintillations, and daytime amplitude scintillations always took place simultaneously for most of the GPS satellites which appeared over Guilin in different azimuth directions. Ground-based GPS scintillation/TEC observations recorded at Guilin and signal-to-noise-ratio (SNR) measurements obtained from GPS-COSMIC radio occultation indicate that nighttime and daytime scintillations are very likely caused by ionospheric F region irregularities and sporadic E, respectively. Moreover, strong daytime amplitude scintillations may be associated with the plasma density enhancements in ionospheric E region caused by the Perseid and Geminid meteor shower activities.     

Very low frequency interferometry for the Chang’E-2 project

Very low frequency interferometry among two astronomical experiments has been proposed and accepted for further study for the second phase of China’s lunar exploration programme (the Chang’E Programme), which is envisaged to operate a lander and a rover on the surface of the moon. This experiment is an interferometer experiment in the very low frequency (VLF, f < 15 MHz) regime of radio frequencies with at least degree-level angular resolution. The goals include observing solar storm activities, Coronal Mass Ejections, Auroral Kilometric Radiation, and planetary radiation in the solar system, studying the origin of Cosmic Rays, spectral properties of pulsars, surveying ionized hydrogen in the Galaxy, and exploring coherent radio emissions.     

基于剪裁技术考虑的某冲击试验分析

利用环境工程剪裁技术对某冲击试验的结果进行分析,结果表明,按照引用标准评定为"超差"的试验,当考虑到试验件结构的特性并进行必要的数据转换后,试验结果是有效。首先分析造成超差的原因为天线组件的剩余响应,然后通过频域数字滤波进行数据转换。