Basic performance of BeiDou-2 navigation satellite system used in LEO satellites precise orbit determination

The visibility for low earth orbit（LEO） satellites provided by the BeiDou-2 system is analyzed and compared with the global positioning system（GPS）. In addition, the spaceborne receivers＇ observations are simulated by the BeiDou satellites broadcast ephemeris and LEO satellites orbits. The precise orbit determination（POD） results show that the along-track component accuracy is much better over the service area than the non-service area, while the accuracy of the other two directions keeps at the same level over different areas. However, the 3-dimensional（3D） accuracy over the two areas shows almost no difference. Only taking into consideration the observation noise and navigation satellite ephemeris errors, the 3D accuracy of the POD is about30 cm. As for the precise relative orbit determination（PROD）, the 3D accuracy is much better over the eastern hemisphere than that of the western hemisphere. The baseline length accuracy is 3.4 mm over the service area, and it is still better than 1 cm over the non-service area. This paper demonstrates that the BeiDou regional constellation could provide global service to LEO satellites for the POD and the PROD. Finally, the benefit of geostationary earth orbit（GEO） satellites is illustrated for POD.     

Dynamics and operation optimization of partial space elevator with multiple climbers

This work studies the dynamics and optimal stabilization method of a partial space elevator (PSE) system with multiple climbers. All satellites and climbers are assumed as lumped masses that are connected by straight, massless, and inextensible tethers. A general dynamic model is derived for the PSE with multiple climbers. It is found different climber moving patterns of climbers have major influence of dynamic behavior of PSE. Optimal control is used to develop optimal operation modes to suppress the libration of PSE with multiple climbers. Moreover, a new operation mode is proposed to approach the desired mission objectives. It is found that all libration angles can be suppressed to zero by the end of the transfer period if two climbers can be kept at a constant speed. At the same time, the magnitudes of libration angles can be kept bounded by regulating the speed of the middle climber relative to other two climbers.     

The heart-shaped supernova remnant 3C 391 viewed in multi-bands

Using Chandra X-ray, Spitzer mid-IR, and 1.5 GHz radio data, we examine the spatial structure of SNR 3C 391. The X-ray surface brightness is generally anti-correlative with the IR and radio brightness. The multiband data clearly exhibit a heart-shaped morphology and show the multi-shell structure of the remnant. A previously unseen thin brace-like shell on the south detected at 24 μm is projected outside the radio border and confines the southern faint X-ray emission. The leading 24 μm knot on the SE boundary appears to be partly surrounded by soft X-ray emitting gas. The mid-IR emission is dominated by the contribution of the shocked dust grains, which may have been partly destroyed by sputtering.     

快速成形法及应用可能分析

简要介绍快速成形技术和一种典型快速成形机的工作原理，并阐述了此技术的主要用途、应用方法及应用可行性分析。     

Energy absorption features of 3-D braided rectangular composite under different strain rates compressive loading

There are huge potential applications of 3-D braided composite in aerospace engineering because of the non-delamination feature of the composite under impact loading. This paper presents the analysis of energy absorption features of 3-D braided composite under compression with different strain rates. The 3-D 4-step rectangular braided composite coupons were tested on a material tester MTS 810.23 and a split Hopkinson pressure bar (SHPB) apparatus to obtain out-of-plane and in-plane compression stress vs. strain curves at quasi-static and high strain rate state. The failure modes and energy absorption features of the 3-D braided composite under different strain rates were analyzed both in time domain and frequency domain. The energy absorbed by the 3-D braided composite increases with the strain rate. From fast Fourier transform (FFT) analysis of compression stress vs. time histories, the power of energy absorption of the 3-D braided composite increases with strain rate and mostly concentrate on the high frequency region. While for quasi-static compression, the power distributes in very narrow frequency region and also is less than that in high strain rates. This feature corresponds to the different damage and energy absorption mechanisms of the 3-D braided composite under quasi-static and high strain rate compression.     

不同温度下DSM11镍基高温合金热腐蚀试验

为了研究DSM11镍基高温合金的抗热腐蚀性能，对该合金在650、750、850℃条件下涂覆5%NaCl+95%Na 2 SO 4 混合盐膜 进行腐蚀试验。利用金相显微镜（OM）、扫描电子显微镜（SEM）、能谱仪（EDS）和X射线衍射仪（XRD）等手段，对合金被腐蚀200 h 后的表面形貌、物相组成、元素和腐蚀层的分布情况以及腐蚀机理进行分析。结果表明：随着试验温度的升高，合金表面腐蚀程度 逐渐加重、腐蚀产物组成逐渐复杂、失重加大、腐蚀产物层厚度增大；合金的腐蚀产物层均可分为3层，最外层和中间层主要为氧 化物，内层由颗粒状氧化物和硫化物组成，O和S的侵入现象表明合金发生了较明显的内氧化与内硫化现象；在3种温度下，合金 表面生成连续稳定的Al 2 O 3 保护层，抑制了热腐蚀反应的进行，对基体存在有效的保护作用，表明合金具有一定的抗热腐蚀性能。     

基于多特征点参数权值优化的蒙皮点云去噪研究

点云去噪的效果对三维扫描过程后续的曲面拟合与造型设计至关重要，如何快速准确提取特征点已成为研究热点，然而点云去噪的关键之处在于奇异值与离群值的检测。提出耦合多特征点参数的去噪模型，分别讨论每个特征点参数对去噪模型的影响程度；采用群智能算法求解出一组最优参数权重，以此确定点云去噪模型，从而达到三维散乱点云最优去噪效果；通过对Bunny 模型进行去噪仿真以及某一型号的蒙皮进行去噪实验，对去噪模型进行验证。结果表明：本文提出的点云去噪模型相较于半径滤波器、统计滤波器、改进体素滤波结合高斯滤波模型，迭代更快、耗时更少，具有更好的去噪效果。     

Initial virtual flight test for a dynamically similar aircraft model with control augmentation system

To satisfy the validation requirements of flight control law for advanced aircraft,a wind tunnel based virtual flight testing has been implemented in a low speed wind tunnel.A 3-degree-offreedom gimbal,ventrally installed in the model,was used in conjunction with an actively controlled dynamically similar model of aircraft,which was equipped with the inertial measurement unit,attitude and heading reference system,embedded computer and servo-actuators.The model,which could be rotated around its center of gravity freely by the aerodynamic moments,together with the flow field,operator and real time control system made up the closed-loop testing circuit.The model is statically unstable in longitudinal direction,and it can fly stably in wind tunnel with the function of control augmentation of the flight control laws.The experimental results indicate that the model responds well to the operator's instructions.The response of the model in the tests shows reasonable agreement with the simulation results.The difference of response of angle of attack is less than 0.5°.The effect of stability augmentation and attitude control law was validated in the test,meanwhile the feasibility of virtual flight test technique treated as preliminary evaluation tool for advanced flight vehicle configuration research was also verified.     

三维工序模型的演进式构建方法

为实现以三维工序模型为核心的三维工艺构建,基于从毛坯模型到最终产品模型的演进过程,对三维工序模型的生成方法进行研究.在制造特征信息模型的基础上,结合基准信息建立了面向工序模型生成的工序信息模型.提出制造特征信息在工序模型中的映射机制,解决该模式下工序模型信息缺失的问题.以工序信息模型为模板,首先定义加工特征基元,然后通过实例化实现工序模型的变换.最后,通过集成工艺决策系统,构建三维工序模型生成系统,为后续工艺尺寸标注和工艺展示提供模型支持.     

多用酸洗缓蚀剂DSCH-1的研究

由含氮的脂肪胺、芳香胺等多种常用的有机缓蚀剂复配制成的ＤＳＣＨ－１ 缓蚀剂，在硝酸中对２０＃ 锅炉钢和紫铜的缓蚀效率达９９．７％ ，在盐酸中对２０＃ 锅炉的钢的缓蚀效率达９８．５％ ，对紫铜的缓蚀效率也较高。Ｆｅ３＋ 离子浓度对ＤＳＣＨ－１ 缓蚀性能有较大的影响