基于MHSS算法的ARAIM完好性和可用性预测

传统的接收机自主完好性监视只能提供非精密进近阶段的完好性监视,无法实现对完好性要求更加严格的飞行阶段的监视,而高级接收机自主完好性监视（AdvancedReceiverAutonomousIntegrityMonitoring,ARAIM）可以在精密进近阶段为飞机提供满足航向信标性能垂直引导（LocalizerPerformancewithVerticalguidance,LPV）的完好性监视服务。文章基于多假设分组解算法,根据目前的星座环境,结合民航不同飞行阶段的应用需求,对ARAIM算法进行仿真研究。针对水平保护级（HorizontalProtectionLevel,HPL）和垂直保护级（VerticalProtectionLevel,VPL）的指标,在不同星座组合环境下,选取南北半球不同经纬度的5个观测机场,分别仿真了HPL和VPL的变化情况,并对全球HPL和VPL平均分布趋势,以及以99%的概率满足LPV-200进近可用性指标时,ARAIM可用性的全球覆盖率进行了仿真预测分析。仿真结果表明,不论是全球定位系统和格洛纳斯双星座还是增加北斗卫星导航系统后的三星座,5个观测机场的HPL和VPL均能满足LPV-200进近对完好性指标的要求;但在全球范围内,双星座条件下,ARAIM并不能完全支持LPV-200进近对完好性监视的要求,而三星座则可大大提高ARAIM的可用性,为民航用户提供满足精密进近的所需导航服务性能。     

利用GNSS实现高轨卫星自主导航的新方案

针对GNSS应用于GEO卫星导航存在的导航信号弱、可见卫星少、定位几何差等突出问题,探讨了一种在GPS导航星冲天面安装导航天线并辐射导航信号的新方案,设计了冲天面天线和GEO接收天线的波束宽度和增益以及讨论了冲天天线所需发射功率,分析了新方案中GEO卫星对GPS卫星可见性、GDOP和定位精度。分析表明,新方案仅需从现有导航星引出一部天线,即可实现以小于10W的功率代价使得GEO卫星80%以上的时间里可以利用GPS系统定位,且定位精度约77m。通过仿真验证了本方案的可行性。     

X-ray pulsar navigation method for spacecraft with pulsar direction error

In order to reduce the impact of the pulsar direction error on the navigation system performance, a novel X-ray pulsar navigation technique is proposed. Through analyzing the system bias caused by the pulsar direction error, it can be seen that the system bias is slowly time-varying. Based on the analysis result, the augmented state unscented Kalman filter (ASUKF), in which the system bias is treated as the augmented state, is designed here to deal with the system bias and estimate spacecraft’s positions and velocities. The simulation results demonstrate the effectiveness and robustness of the proposed navigation method. The ASUKF-based navigation method for spacecraft is more accurate than the method based on unscented Kalman filter (UKF) in the presence of the pulsar direction error.     

Onboard orbit determination using GPS observations based on the unscented Kalman filter

Spaceborne GPS receivers are used for real-time navigation by most low Earth orbit (LEO) satellites. In general, the position and velocity accuracy of GPS navigation solutions without a dynamic filter are 25 m (1σ) and 0.5 m/s (1σ), respectively. However, GPS navigation solutions, which consist of position, velocity, and GPS receiver clock bias, have many abnormal excursions from the normal error range for space operation. These excursions lessen the accuracy of attitude control and onboard time synchronization. In this research, a new onboard orbit determination algorithm designed with the unscented Kalman filter (UKF) was developed to improve the performance. Because the UKF is able to obtain the posterior mean and covariance accurately by using the second-order Taylor series expansion through the sampled sigma points that are propagated by using the true nonlinear system, its performance can be better than that of the extended Kalman filter (EKF), which uses the linearized state transition matrix to predict the covariance. The dynamic models for orbit propagation applied perturbations due to the 40 × 40 geo-potential, the gravity of the Sun and Moon, solar radiation pressure, and atmospheric drag. The 7(8)th-order Runge–Kutta numerical integration was applied for orbit propagation. Two types of observations, navigation solutions and C/A code pseudorange, can be used at the user’s discretion. The performances of the onboard orbit determination were verified using real GPS data of the CHAMP and KOMPSAT-2 satellites. The results of the orbit determination were compared with the precision orbit ephemeris (POE) of the CHAMP and KOMPSAT-2 satellites.     

基于卫星监视几何精度因子的UDRE值估计方法

星基增强导航系统(SBAS,Satellite Based Augmentation System)通过向用户提供用户差分距离误差(UDRE,User Differential Range Error),来保证广播星历和星钟改正数的精度并增强用户的完好性性能.给出了一种用于主控站的UDRE计算方法,提出了卫星监视几何精度因子(SSDOP,Satellite Surveillance Dilution of Precision)的概念.基于UDRE和SS-DOP的表达式,通过数学推导发现UDRE受到SSDOP和限制因子的影响,而限制因子可以用其统计平均值0.7438来替代,建立了由SSDOP估计UDRE的表达式.仿真结果表明:利用SS-DOP估计出的UDRE值,其误差不超过0.8 m,能够反映出当前卫星UDRE的特性,可以作为用户在无法接收完好性信息时快速推算UDRE的一种可行手段.     

反TBM拦截弹杀伤增强器综合设计模型及其应用

针对反战术弹道式导弹(TBM)拦截弹杀伤增强器设计方法中存在的不足,提出了拦截平面内最优合成迎角数学模型,在此基础上建立了拦截弹杀伤增强器综合设计模型.该模型以杀伤增强器参数为输入量,可在设计拦截弹时对其进行可用过载估计与制导精度限制,并通过最优合成迎角控制来近一步增强拦截弹对TBM的杀伤性能.以PAC-3拦截弹及某典型TBM弹头为例进行仿真验证,结果表明采用综合设计模型后PAC-3杀伤概率平均高于原弹约7％,使用该模型对PAC-3杀伤增强器进行优化,优化结果明显提高了PAC-3拦截弹的作战性能.     

MTF对立体测绘高程精度影响研究

MTF（调制传递函数）是反映测绘相机性能的重要指标,研究MTF对测绘高程精度的影响可以对相机的设计指标提出要求,对提高测绘精度具有极其重要的意义。文章通过计算机仿真的方法进行研究,利用3DStudioMax软件构建三维模型与模拟成像、用Harris算子提取图像特征点,并用奇异值分解与最小二乘法进行特征点的匹配,通过前方...     

用于SiC超光滑表面加工的大气等离子体抛光系统设计

设计了一套基于射频电容耦合放电原理的大气等离子体抛光原型装置,电容耦合等离子体炬首次被应用到了抛光系统中。针对SiC反射镜的加工实验结果表明,系统工作正常,并可以实现亚纳米级的表面粗糙度。     

蓝宝石的纳米压痕试验与有限元仿真研究

在对蓝宝石进行纳米压痕试验的基础上,利用有限单元法建立了纳米压痕试验的数值模型,对蓝宝石的纳米压痕试验进行模拟、计算和分析,确定了蓝宝石表层的材料性能和力学特性.该模型可以研究在加工过程中,主要工艺参数对加工效果、加工效率、所导致的加工表面损伤层的影响,确定它们之间的相互关系,进而优化工艺参数,完善蓝宝石材料精密研磨加工的水平.