降落伞充气环境对充气性能的影响

在降落伞轴向和径向动量方程的基础上进行一些合理的简化,并结合其他经验公式基本描述了降落伞整个充气阶段的运动过程。运用简化的模型初步分析了在不同大气密度、初始开伞速度下的充气环境对降落伞充气时间、充气距离,伞绳最大拉力的影响。得到的结论对火星降落伞设计及降落伞充气试验的环境模拟有一定参考意义。     

无陀螺下基于修正罗德里格参数的星体姿态确定

介绍了修正罗德里格参数(MRP),分析比较了姿态表示参数修正罗德里格参数和四元数的算法特点。通过仿真计算,比较了当卫星受一阶马尔柯夫干扰力矩作用和CCD星敏感器为唯一星载角运动传感器时,分别用修正罗德里格参数和四元数作为姿态表示参数,采用UKF(Unscented Kalman Filter)估计卫星航向、姿态及相应角速率的滤波效果。结果表明,用修正罗德里格参数法的姿态解算精度比用四元数法的姿态解算精度高,且计算效率明显优于四元数算法,计算量仅相当于四元数算法的一半,这是由于四元数的规范化条件(即模值为1),在姿态确定中会导致误差协方差阵奇异,而修正罗德里格参数虽然不是全局非奇异的,但是可以通过切换方法解决奇异性问题。     

风场对舱-伞系统着陆姿态影响的仿真研究

风场对舱-伞系统的落点及姿态稳定性存在不可忽略的影响。文章对某型号飞船在几种不同风场条件下的回收过程进行了仿真研究,着重分析了风对返回舱各项参数的影响,所得结论对回收系统设计具有重要的参考价值。     

双欧法在克服伞-弹系统欧拉方程奇异性中的应用

文章针对伞弹系统欧拉方程奇异性 ,利用正、反欧拉方程精华区、奇异区呈倒挂的原理 ,建立了一套与飞机不同的反欧拉系统。将这套双欧系统应用在克服伞 -弹系统欧拉方程奇异性中 ,取得了满意的结果。同时对双欧法与四元数法计算结果进行了对比验证 ,从而更加清楚地看到了四元数法的方法缺陷和不足 ,为进一步能将双欧法应用于伞 -弹系统六自由度弹道实时仿真进行了有益的尝试     

单片宽带频谱分析芯片设计

文章介绍了单片宽带实时频谱分析芯片的设计原理和方法,并在FPGA上进行了原型验证。设计中采用了基于多相滤波器组的下变频方案,并对下变频后每一路数据进行重叠加窗处理。为了减小芯片面积,对后端的FFT分析模块进行了优化设计,提出了将两条蝶形运算级合并为一条流水线的新型FFT设计构架。该设计可以不间断地处理数据,从而实现信号的无缝捕获。     

伞舱系统在火星环境中的运动特性分析

建立了火星大气环境模型和伞舱系统多体动力学模型,通过仿真分析了火星环境下伞舱系统中进入舱的运动特性,并对其在火星环境和地球环境的运动稳定性进行仿真比较分析,得出的相关结论可为探测器火星登陆技术提供参考。     

裂纹间距及铺层角度对复合材料分层的影响

分层问题是复合材料层合板最常见问题,据统计约60%的层合板失效都与分层相关.通过基于虚裂纹闭合技术(VCCT)的重合网格法(S-FEM),分析了不同铺层角度及裂纹间距对应变能释放率的影响.由分析结果可看出,应变能释放率随铺层角度增加而减小;在裂纹尖端距离相对较小时,距离对能量释放率的影响要远大于锗层角度变化的影响.     

Switching and performance variations of on-orbit BDS satellite clocks

The information of the satellite clock switching and performance variations on-orbit of Chinese BeiDou-2 Navigation System (BDS) is not available for the public. In order to detect the BDS satellite clock switching and performances variation, we analyzed the precise clock offset products with a total duration of 5?years every BDS satellite equipped four atomic clocks from four different manufactures from January 2013 to October 2017. Three important contributions are concluded as follows. (1) It is found that the average time of on-orbit operation for BDS satellite clocks is about 1–2?years. There have been 22 times of clock switching for BDS satellites, of which the C05 and C08 satellites have been switched to the fourth (last) atomic clock. (2) There are frequent phase adjustments for BDS on-orbit satellite clocks, and the frequency series is relatively stable. Furthermore, there are semi-annual sinusoid cycles in the frequency drift series of C06 and C09 satellites. (3) The performances of MEO satellite clocks perform better than the IGSO and GEO satellite clocks. The average ten-thousand frequency stability of BDS satellite clocks is about 1E-13, which is worse than that of GPS and Galileo but better than that of GLONASS.     

Inferring Nighttime Ionospheric Parameters with the Far Ultraviolet Imager Onboard the Ionospheric Connection Explorer

The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.6 nm photons in the ionosphere including the mutual neutralization contribution as well as the effect of resonant scattering by atomic oxygen and pure absorption by oxygen molecules. This forward model is then used in conjunction with a constrained optimization algorithm to invert the anticipated ICON FUV line-of-sight integrated measurements. In this paper, we describe the connection between ICON FUV measurements and the nighttime ionosphere, along with the approach to inverting the measured emission profiles to derive the associated O⁺ profiles from 150–450 km in the nighttime ionosphere that directly reflect the electron density in the F-region of the ionosphere.     

Layer-oriented Element Integration Algorithm of Conformal Perfectly Matched Layer

As an efficient artificial truncating boundary condition, conformal perfectly matched layer (CPML) is a kind of multilayer anisotropic absorbing media. To reduce computing effort of CPML, this article proposes a layer-oriented element integration algorithm. In this algorithm, the relative dielectric constant and permeability are considered as constants for each the very thin monolayer of CPML, and the element integration of multilayer along the normal direction is substituted by the element integration of monolayer. The CPML is divided into multilayer elements, whose element matrixes are evaluated by monolayer integration. Numerical examples show that the layer-oriented element integration algorithm is reliable and the CPML formed with this algorithm possesses high-efficient absorbing performance.