A novel data association scheme for LEO space debris surveillance based on a double fence radar system

The increasing amount of space debris threatens to seriously deteriorate and damage space-based instruments in Low Earth Orbit (LEO) environments. Therefore, LEO space debris surveillance systems must be developed to provide situational awareness in space and issue warnings of collisions with LEO space debris. In this paper, a double fence radar system is proposed as an emerging paradigm for LEO space debris surveillance. This system exhibits several unique and promising characteristics compared with existing surveillance systems. In this paper, we also investigate the data association scheme for LEO space debris surveillance based on a double fence radar system. We also perform a theoretical analysis of the performance of our proposed scheme. The superiority and the effectiveness of our novel data association scheme is demonstrated by experimental results. The data used in our experiments is the LEO space debris catalog produced by the North American Air Defense Command (NORAD) up to 2009, especially for scenarios with high densities of LEO space debris, which were primarily produced by the collisions between Iridium 33 and Cosmos 2251. We hope that our work will stimulate and benefit future work on LEO space debris surveillance approaches and enable construction of the double fence radar system.     

对转双转子系统临界转速求解方法的改进与对比

为解决对转双转子航空发动机临界转速求解的难题,满足转子动力学设计需求,结合商业有限元软件,给出直接法和完全法两种临界转速求解方法,并结合算例详细论述了方法的理论基础和求解过程,最终以谐响应分析结果加以验证.研究结果表明:基于商业有限元软件特征值分析的完全法不需要任何振型信息,就可对正反进动曲线进行区分,极大简化了对转双...     

Improved robust Kalman filter for state model errors in GNSS-PPP/MEMS-IMU double state integrated navigation

The integration of Global Navigation Satellite System (GNSS) with Inertial Navigation Systems (INS) has been actively researched and widely applied as it can provide reliable positioning information continuously. In recent years, Micro Electro Mechanical Systems (MEMS) technology achieves rapid development and Micro Electro Mechanical Systems and Inertial Measurement Unit (MEMS-IMU) has aroused wide concern due to its excellent properties in some cases. However, the observations from MEMS-IMU are easy to be influenced by motion state and location environment because of its manufacturing process. It is not easy to judge whether gross errors are in the state model or the observation model by the widely adopted robust filter based on innovation. In this contribution, we present an improved robust filter with a double state model on the basis of the chi-square distribution of the square of the Mahalanobis distance. The vehicle motion model acts as the external constraint information and can be adopted to construct robust statistic with the results from INS mechanization. And then a robust factor was determined to adjust the observation noise covariance matrix. To evaluate the performance of this method, the simulation test and the field test based on locomotive platform of Nottingham Geospatial Institute (NGI) were carried out. According to the results, in the simulation test, the position improvements are 33%, 30% in the north and east directions; in the real test, the loosely and tightly coupled was adopted and the position accuracy can be improved by about 50–60% in the horizontal direction and the improvement of the pitch and the roll accuracy was lower than the azimuth accuracy due to poor observability and experimental scene which is of the characteristics of small elevation change. Therefore, the proposed robust filter could diminish the effect of the gross error from MEMS-IMU and enhance the integrated system.     

Shocklike soliton because of an impinge of protons and electrons solar particles with Venus ionosphere

This paper introduces an investigation of shocklike soliton or small amplitude Double Layers (DLs) in a collisionless plasma, consisting of positive and negative ions, nonthermal electrons, as well as solar wind streaming protons and electrons. Gardner equation is derived and its shocklike soliton solution is obtained. The model is employed to recognize a possible nonlinear wave at Venus ionosphere. The results indicate that the number densities and velocities of the streaming particles play crucial role to determine the polarity and characteristic features (amplitude and width) of the shocklike soliton waves. An electron streaming speed modifies a negative shocklike wave profile, while an ion streaming speed modulates a positive shocklike wave characteristic.     

在轨服务飞行器自动寻的段的接近策略分析

在轨服务飞行器在自主式在轨服务系统中发挥重要作用,实现在轨服务飞行器与目标服务对象间的交会是在轨服务任务过程的必要阶段。为优化交会过程自动寻的段的接近策略,对基于Hill方程的双冲量机动策略进行了分析,讨论了在轨服务飞行器的初始轨道参数和机动时间选择对接近过程的影响。运用典型算例,得出两航天器的轨迹、速度和机动消耗在不同坐标系的变化规律,指出了算例中机动消耗随在轨服务飞行器初始参数变化的特点。     

双补燃室固冲凝聚相颗粒分布对比试验研究

针对固冲发动机燃烧效率较低以及凝相粒子分布规律不清楚的现状,本文建立了一套评价固冲发动机燃烧效率的双补燃室试验装置和研究凝相颗粒分布的取样装置。对比研究了结构相同的补燃室内的参数,其误差小于0.5%,说明该装置可以用于精确对比不同补燃室的燃烧效率。然后应用该装置完成了补燃室长度分别为600mm、800mm、1000mm,进气角度分别为30°、45°、60°的对比试验,分析了粒子的粒度分布规律和化学成分变化规律,该规律与数值分析的规律相同。试验结果表明：在进气角度不变情况下,补燃室长度增加有利于提高燃烧效率,燃烧室压强提高,凝相粒子直径明显减小,B粒子燃烧更充分;在补燃室长度为1000mm的情况下,进气角度增加有利于燃烧效率增加,燃烧室压强提高,粒子直径减小,B粒子燃烧更充分。双补燃室发动机是评价补燃室燃烧效率的有效装置,粒度分布和燃烧产物的化学成分有助于补燃室结构设计。     

导航卫星系统总体研究及星座改进方案仿真

我国的双星导航定位系统是我国第一代卫星导航定位系统,采用“有源 应答”的定位机制,用于中、低动态用户的区域导航定位,与国外卫星导航定位系 统相比有自己的长处和不足。为满足对高速运动的精确制导武器导航定位的需 要,本文提出了一种星座改进方案,并进行了仿真研究。仿真结果显示此方案可 以满足在我国及周边地区导航定位的精度要求。     

三种钻头钻削CFRP的制孔损伤对比

采用二刃双锋角钻头、三刃双锋角钻头和圆弧形钻头在不同加工参数下钻削CFRP,对比分析了孔入出口质量(入口损伤、毛刺和出口撕裂),并采用毛刺存在角度来衡量毛刺的多少。结果表明:随着进给量的增大毛刺存在的角度(范围)α先减小后增大;综合考虑孔入口和出口质量(毛刺和撕裂因子),三刃双锋角钻头最适合钻CFRP。     

固体推进剂火箭发动机贮存性能规律研究

依据固体推进剂火箭发动机大量试验数据的统计规律，提出了估算固体推进剂火箭发动机主要参量随贮存年限、温度变化而改变的数学关系式：R^1=KRR0(1 a)^△t-1，并通过了反算、验证试验和实际中的应用。     

双陶瓷层热障涂层3.5％Y2O3-La2(Zr0.7Ce0.3)2O7/YSZ研究

采用EB-PVD沉积了3.5％Y2O3-La2(Zr0.7Ce0.3)2O7(3.5Y-LZ7C3)/YSZ双陶瓷热障涂层,分析了涂层的成分、相结构、组织形貌和热循环氧化性能.研究表明:La2(Zr0.7Ce0.3)2O7(LZ7C3)材料中掺杂Y2O3能有效地降低涂层中La2O3/ZrO2/CeO2的成分偏差;双陶瓷涂层在1050℃下氧化增重动力学为M=0.1219t1/3,相比抛物线型YSZ涂层的氧化增重曲线,较大减缓了氧化速度;沉积态双陶瓷涂层表面结构(即3.5Y-LZ7C3涂层结构)为烧绿石结构,经过热循环后逐渐分解,出现了萤石结构以及La2O3的衍射峰;在1050℃双陶瓷层热循环氧化寿命达768h.