速度增益制导在远程交会任务中的应用

利用冲量假设解决远程交会问题在工程上很难实施,制导精度无法控制。本文针对两冲量交会问题,设计出两次机动的制导方案。第一次机动利用速度增益制导,第二次机动采用按时间关机制导。理论和仿真结果显示该方案可靠性高,制导精度满足远程交会的技术要求,同时也保证了向近程制导转换的精度。     

间接SLS制造金属零件初坯尺寸精度研究

本文选取还原铁粉与环氧树脂的混和粉粉末作为间接SLS成型材料,采用正交试验的方法研究了间接SLS成型金属零件初坯的尺寸精度,并探讨了影响尺寸精度因素。结果表明:粘结剂体积随温度变化特性和其随激光能量密度变化分解程度是引起初坯尺寸变化的最主要因素;激光扫描间距的选取也会影响初坯X,Y方向的精度;当切片层厚为0.12 mm,扫描间距为0.13,扫描速度为1 900-1 950 mm/s,激光功率为12 W时,初坯的尺寸维持较好。     

一类基于非等距单元平均重构的高效差分格式

构造了一维非线性双曲型守恒律的一类基于非等距单元平均值的点值重构的高精度高分辨率守恒型差分格式。其构造思想是:首先,将计算区间划分为若干个互不重叠的小区间,再根据格式精度的要求利用Gauss-Lobatto点和Gauss-Chebyshev点划分小区间,通过各非等距细小区间上的单元平均值,重构各细小区间交界面上的点值,并加以校正;其次,利用近似Riemann解计算细小区间交界面上的数值通量,并结合高阶Runge-Kutta TVD时间离散方法,得到了高精度的全离散方法。证明了该格式的无振荡特性。然后,将格式推广到一维双曲型守恒方程组情形。最后,给出了几个标准数值算例,验证了格式的高效性。     

A multi-objective optimization framework of constellation design for emergency observation

To meet the urgent needs of emergency observation missions, a well-designed constellation is key to ensuring system performance. This paper presents a multi-objective optimization framework which is well suited for constellation designers to identify key trade-offs and make decisions. Firstly, this work investigates the metrics of responsiveness and coverage simultaneously to approximate to the actual conditions of emergencies, and a multi-objective mathematical model is constructed to explore solutions to enhance the overall system performance. Then, according to the characteristics of emergency missions, a hierarchical chromosome encoding method is proposed in the framework to encode a solution that explores different sized constellations without constraining its specific geometry. Finally, we propose the use of radial axes plots to help constellation designers to gain pragmatic insights for informed decision making. The simulation of disaster management verifies that the proposed chromosome encoding method effectively promotes the convergence of the algorithm, and the multi-objective optimization framework helps to generate a rapid and adequate observation satellite constellation to provide maximum coverage performance while ensuring timeliness.     

Simulation of the land surface temperature from moon-based Earth observations

The land surface temperature (LST) is a key parameter for the Earth’s energy balance. As a natural satellite of the Earth, the orbital of the moon differs from that of current Earth observation satellites. It is a new way to measure the land surface temperature from the moon and has many advantages compared with artificial satellites. In this paper, we present a new method for simulating the LST measured by moon-based Earth observations. Firstly, a modified land-surface diurnal temperature cycle (DTC) method is applied to obtain the global LST at the same coordinated universal time (UTC) using the Moderate Resolution Imaging Spectroradiometer (MODIS) LST products. The lunar elevation angles calculated using the ephemeris data (DE405) from the Jet Propulsion Laboratory (JPL) were then applied to simulate the Earth coverage observed from the moon. At the same time, the modified DTC model was validated using in situ data, MODIS LST products, and the FengYun-2F (FY-2F) LST, respectively. The results show that the fitting accuracy (root-mean-square error, RMSE) of the modified DTC model is not greater than 0.72?°C for eight in situ stations with different land cover types, and the maximum fitting RMSE of the modified model is smaller than that of current DTC models. By the comparison of the simulated LST with MODIS and FY-2F LST products, the errors of the results were feasible and accredited, and the simulated global LST has a reasonable spatiotemporal distribution and change trend. The simulated LST data can therefore be used as base datasets to simulate the thermal infrared imagery from moon-based Earth observations in future research.     

临近空间高超声速飞行器天文导航系统综述

临近空间是航天与航空业务领域的结合部，具有重要的战略价值。高超声速飞行器是临近空间力量部署的重要载体，已逐渐进入应用部署阶段。临近空间高超声速飞行器的飞行环境和任务条件对导航系统提出了新的更高要求。在总结临近空间高超声速飞行器的导航技术研究进展的基础上，对天文导航技术的应用环境和条件进行了系统的分析和探讨，提出了5个重点研究方向，包括：星图采集效能、光学误差模型、视场观测机理、姿态更新速率、小型化模块化工程化等。研究结果可为临近空间高超声速飞行器天文导航系统的设计提供参考。     

CFD中统计误差的数值精度分析

在计算流体力学（CFD）的算法研究中经常会对离散误差进行数值精度分析，通常以统计误差的各范数为研究对象，最常用的统计误差范数为L₁范数、L₂范数和L_∞范数，一般认为各范数在数值精度上具有等价性。实际上，由于流场局部存在间断、网格局部不连续或者是在极值点附近采用非线性加权插值等可能使数值方法存在局部降阶问题，导致统计误差各范数所表达的数值精度并不一致。通过详细的理论分析，揭示了统计误差各范数所表达的数值精度之间的关系，并通过相应的数值试验予以验证。研究结果不仅能够指导CFD算法的数值精度验证工作，而且也可为更为复杂流动模拟的数值精度判定提供理论依据。     

A novel range-Doppler imaging algorithm with OFDM radar

Traditional pulse Doppler radar estimates the Doppler frequency by taking advantage of Doppler modulation over different pulses and usually it requires a few pulses to estimate the Doppler frequency. In this paper, a novel range-Doppler imaging algorithm based on single pulse with orthogonal frequency division multiplexing(OFDM) radar is proposed, where the OFDM pulse is composed of phase coded symbols. The Doppler frequency is estimated using one single pulse by utilizing Doppler modulation over different symbols, which remarkably increases the data update rate. Besides, it is shown that the range and Doppler estimations are completely independent and the well-known range-Doppler coupling effect does not exist. The effects of target movement on the performances of the proposed algorithm are also discussed and the results show that the algorithm is not sensitive to velocity. Performances of the proposed algorithm as well as comparisons with other range-Doppler algorithms are demonstrated via simulation experiments.     

机载空空导弹武器系统精度评估方法

研究了用系留飞行数据计算、分析和评价武器系统精度的详细方法,并给出了典型分析实例,通过在机载空空导弹武器系统研制和载机加挂先进空空导弹项目的应用,验证了其正确性和实用性.     

基于光电延时法的激光测距精度测试系统

介绍了一种激光测距精度测试系统,系统采用了光电延时模拟距离的原理,实现了对激光测距机测距范围（500～20 000）m内测距精度的测量。测试系统具有高测量精度、高分辨力、易操作、实用性强的特点。