State and disturbance estimation for test masses of drag-free satellites based on self-recurrent wavelet neural network

In recent years, the drag-free satellites have been widely used for some fundamental physical experiments, such as checking short-range effects of general relativity, geopotential determination and the exploration of static ocean current. And the space-borne detector of gravitational waves is one of the important applications for drag-free satellites in the future. In this study, the estimation of relative motion state and disturbance for test masses of drag-free satellite after release are researched. Firstly, the relative motion model between the test masses is established based on corresponding reference frames. Secondly, a self-recurrent wavelet neural network estimator is designed to estimate the pure gravitational relative motion state and disturbance for the test masses, and the sliding mode controller is used to transfer the relative motion state to the ideal state. Finally, the proposed estimation methods are verified by the simulation results.     

航母编队防空作战预警纵深对警戒直升机前出距离的约束分析

航母编队在防空时,通常利用舰载警戒直升机机载警戒雷达探测距离远的优势实施对空预警,以提高编队防空作战能力。通过分析航母编队在舰载战斗机甲板待战情况下的防空作战过程,建立了警戒直升机前出距离的数学模型,仿真分析了模型中有关参数对警戒直升机前出距离的影响,为确定警戒直升机在航母编队防空作战中的前出距离提供了参考依据。     

Modeling spatial density in low earth orbits using wavelets and random search

The events that occurred after 2007 such as Chinese anti-satellite test, explosion of Briz-M upper stage, break up of cosmos-2421 and collision of cosmos-2251 with Iridium-33 satellites have completely changed the spatial density patterns in low earth orbits. This has increased the risk of collision between active satellites and debris created by them. Aftermath, the risk assessment of possible collisions called as conjunction analysis of working satellites from day to day has become more crucial. Spatial density models are useful in understanding the long-term likelihood of a collision in a particular region of space and helpful in pre-launch orbit planning. In this paper we present an algorithmic procedure for automatically estimating exact model parameters corresponding to the peak location and number of peaks using wavelets that will speed up the parameter estimation process for the models with peaks.     

方位-距离接收机电流漂移故障研究

研究了某型机载近程导航系统接收机的航向和下滑线信号因装备时间长引起电流漂移，从而导致引导飞机正常着陆的信号误差变大的具体原因，分析了着陆信号变换器的失效机理，给出了关键节点的理论推导过程和参考标准值，通过采取针对性的解决措施，从根本上提高飞机在着陆过程中的飞行安全性。     

FrFT-CSWSF:Estimating cross-range velocities of ground moving targets using multistatic synthetic aperture radar

Estimating cross-range velocity is a challenging task for space-borne synthetic aperture radar（SAR）, which is important for ground moving target indication（GMTI）. Because the velocity of a target is very small compared with that of the satellite, it is difficult to correctly estimate it using a conventional monostatic platform algorithm. To overcome this problem, a novel method employing multistatic SAR is presented in this letter. The proposed hybrid method, which is based on an extended space-time model（ESTIM） of the azimuth signal, has two steps： first, a set of finite impulse response（FIR） filter banks based on a fractional Fourier transform（FrFT） is used to separate multiple targets within a range gate; second, a cross-correlation spectrum weighted subspace fitting（CSWSF） algorithm is applied to each of the separated signals in order to estimate their respective parameters. As verified through computer simulation with the constellations of Cartwheel, Pendulum and Helix, this proposed time-frequency-subspace method effectively improves the estimation precision of the cross-range velocities of multiple targets.     

Model-based robust estimation and fault detection for MEMS-INS/GPS integrated navigation systems

In micro-electro-mechanical system based inertial navigation system（MEMS-INS）/global position system（GPS） integrated navigation systems, there exist unknown disturbances and abnormal measurements. In order to obtain high estimation accuracy and enhance detection sensitivity to faults in measurements, this paper deals with the problem of model-based robust estimation（RE） and fault detection（FD）. A filter gain matrix and a post-filter are designed to obtain a RE and FD algorithm with current measurements, which is different from most of the existing priori filters using measurements in one-step delay. With the designed filter gain matrix, the H-infinity norm of the transfer function from noise inputs to estimation error outputs is limited within a certain range; with the designed post-filter, the residual signal is robust to disturbances but sensitive to faults. Therefore, the algorithm can guarantee small estimation errors in the presence of disturbances and have high sensitivity to faults. The proposed method is evaluated in an integrated navigation system, and the simulation results show that it is more effective in position estimation and fault signal detection than priori RE and FD algorithms.     

装备研制费用参数估算方法研究

参数法是进行装备研制费用估算的有效方法之一.介绍了参数费用估算的历史和基本原理,分析了装备研制费用的主要驱动因素,将其作为估算参数,并给出了装备研制费用参数估算的基本流程.最后,基于国际先进的参数估算软件True Planning,对国外新一代直升机进行了参数估算的实例研究,显示了参数估算的有效性.     

基于倒谱的运动模糊图像参数估计方法

通过分析运动模糊图像点扩展函数的倒谱特性,提出了基于倒谱特性的运动模糊参数估计方法。仿真实验结果与理论分析一致,验证了理论分析的正确性。数值实验表明,该方法具有较高的准确性,且具有较强的鲁棒性。     

一种基于DFT的高精度载波频偏估计算法

针对无线数字通信中的载波频率同步问题,提出一种新的载波频偏估计算法。利用离散傅里叶变换（DFT）内插技术,在较大频偏范围内估计出载波频偏,并且在估计精度上相对于DFT法有了很大的提高。这种算法不需要增加DFT数据长度,适合突发通信方式。进行了Monte Carlo仿真实验,仿真结果表明新算法不仅具有宽的估计范围,还具有高的估计精度。     

基于Webservice的个别指导式远程学习软件及知识设计策略

建构个别指导式远程学习软件的系统模型,根据认知心理学领域,知识分为陈述性知识和程序性知识,主要讨论知识库模型中,针对不同的知识选择不同的设计策略,以增加软件的可读性,使学生能进行高效率地学习.