高强阻尼铝合金的阻尼性能和组织稳定性

采用时效处理实验,研究了快速凝固/粉末冶金工艺制备的X7093/5(Zn-30Al)高强度阻尼铝合金的阻尼性能和组织稳定性.将阻尼铝合金分别在50℃,100℃,120℃保温10?h,50?h,100?h后空冷,采用动态力学热分析仪(DMTA)和透射电镜(TEM)分别测试其阻尼性能和观察微观组织的变化情况.研究结果表明: 阻尼铝合金在时效过程中,组织结构由最初细碎杂乱的晶态结构转变为具有规则晶界的大晶粒结构,晶界对合金阻尼性能的贡献增强.在室温至250℃的温度范围内,合金阻尼值由4×10^-3增至3.0×10^-2.阻尼铝合金在120℃以下、100?h以内的时效处理中,时效温度和时效时间的不同对合金阻尼性能的影响不显著,材料的阻尼性能稳定性良好.     

GPS和类GPS测距技术在双星编队星座状态确定中的联合应用

为提高状态确定的精度,借鉴AFF技术引入一种辅助手段——类似GPS的伪距和载波相位测距技术(简称类GPS测距技术)．它的伪码码元和载波相位波长比GPS的更短,因而可获得更高精度的相对测量信息．针对对地观测的双星编队星座的状态确定任务,建立了联合GPS和类GPS测距技术进行编队星座状态整体确定的数学模型,并快速同时解算出GPS星间单差模糊度和类GPS星内单差模糊度,最后进行了数学仿真．仿真结果表明,编队状态的精度有明显提高,其中相对位置精度为10~(-3)m,姿态角精度为10~(-4)rad．仿真证明该方法有效．     

微捷联姿态系统的一种扩展卡尔曼滤波方法

采用低精度的微惯性陀螺和加速度计作为微惯性捷联姿态确定系统元件,首先分析了捷联惯性姿态解算的非线性问题和误差累积的原因;根据姿态三角函数关系引入横滚、俯仰角的3个替换变量作为状态变量,并根据状态变量之间的约束方程和运动体前向速度测量,建立了捷联惯性姿态的一种扩展卡尔曼滤波模型;采用MTi微惯性捷联测量组合进行实验,将该扩展卡尔曼滤波方法解算载体姿态结果与捷联姿态解算结果相比较,验证了该方法抑制惯性姿态解算累积误差的能力.      

卫星初始轨道确定方法研究

卫星精密轨道确定过程实际上是通过求解轨道动力学微分方程组而对初始轨道不断改进的过程,因此,轨道确定的精度与速度不但依赖于求解微分方程组的具体算法,同样依赖于初始轨道的精度与准确性。针对多站测距/距离和数据,建立了一种轨道初值计算的几何方法,该方法集折射误差修正方法于一体,在进行观测数据折射误差修正的基础上,可以得到卫星在任意时刻的轨道初值。     

Accurate orbit predictions for debris orbit manoeuvre using ground-based lasers

Orbit manoeuvre of low Earth orbiting (LEO) debris using ground-based lasers has been proposed as a cost-effective means to avoid debris collisions. This requires the orbit of the debris object to be determined and predicted accurately so that the laser beam can be locked on the debris without the loss of valuable laser operation time. This paper presents the method and results of a short-term accurate LEO (<900 km in altitude) debris orbit prediction study using sparse laser ranging data collected by the EOS Space Debris Tracking System (SDTS). A main development is the estimation of the ballistic coefficients of the LEO objects from their archived long-term two line elements (TLE). When an object is laser tracked for two passes over about 24 h, orbit prediction (OP) accuracy of 10–20 arc seconds for the next 24–48 h can be achieved – the accuracy required for laser debris manoeuvre. The improvements in debris OP accuracy are significant in other applications such as debris conjunction analyses and the realisation of daytime debris laser tracking.     

基于广义正则化最小二乘的天基测向初定轨

传统天基测向初定轨的不足,主要是由于观测数据存在系统误差和观测方程组的系数矩阵病态或不可逆。文章建立观测方程的半参数回归模型,提出基于补偿最小二乘估计和岭估计的广义正则化最小二乘估计,推导了估计公式,并证明了相关统计性质。引入选主列Givens-QR分解算法,提高观测方程求解效率和数值计算稳定性。仿真结果表明:该方法应用于天基测向初定轨可行,可以提高定轨精度和解算成功率。     

新的GPS单频单历元定姿算法

LAMBDA算法依赖于初始的模糊度浮点解,但仅用载波相位观测方程需要多个历元才能获得浮点解,将导致初始化时间过长.针对这一问题,对GPS(Global Positioning System)单历元的载波相位单差方程进行特殊变换,将未知的整周模糊度看成噪声,从而构造出新的观测方程,和原始的观测方程进行组合求解,克服了仅用载波相位双差观测方程因为亏秩而无法在单历元获得浮点解的缺点,解决了初始化时间的问题.通过深入研究浮点解和固定解之间的关系,提出一种将低精度浮点解映射到固定解的方法,降低了LAMBDA算法对高精度浮点解的依赖性,避免了用多个历元获取浮点解的高精度,从而实现了单频、单历元的整周模糊度估计.通过实际测试,该算法成功率高于97%,能够有效地用于实时动态姿态解算.      

Generating precise and homogeneous orbits for Jason-1 and Jason-2

Driven by the GMES (Global Monitoring for Environment and Security) and GGOS (Global Geodetic Observing System) initiatives the user community has a strong demand for high-quality altimetry products. In order to derive such high-quality altimetry products, precise orbits for the altimetry satellites are a necessity. With the launch of the TOPEX/Poseidon mission in 1992 a still on-going time series of high-accuracy altimetry measurements of ocean topography started, continued by the altimetry missions Jason-1 in 2001 and Jason-2/OSTM in 2008. This paper contributes to the on-going orbit reprocessing carried out by several groups and presents the efforts of the Navigation Support Office at ESA/ESOC using its NAPEOS software for the generation of precise and homogeneous orbits referring to the same reference frame for the altimetry satellites Jason-1 and Jason-2. Data of all three tracking instruments on-board the satellites (beside the altimeter), i.e. GPS, DORIS, and SLR measurements, were used in a combined data analysis. About 7 years of Jason-1 data and more than 1 year of Jason-2 data were processed. Our processing strategy is close to the GDR-C standards. However, we estimated slightly different scaling factors for the solar radiation pressure model of 0.96 and 0.98 for Jason-1 and Jason-2, respectively. We used 30 s sampled GPS data and introduced 30 s satellite clocks stemming from ESOC’s reprocessing of the combined GPS/GLONASS IGS solution. We present the orbit determination results, focusing on the benefits of adding GPS data to the solution. The fully combined solution was found to give the best orbit results. We reach a post-fit RMS of the GPS phase observation residuals of 6 mm for Jason-1 and 7 mm for Jason-2. The DORIS post-fit residuals clearly benefit from using GPS data in addition, as the DORIS data editing improves. The DORIS observation RMS for the fully combined solution is with 3.5 mm and 3.4 mm, respectively, 0.3 mm better than for the DORIS-SLR solution. Our orbit solution agrees well with external solutions from other analysis centers, as CNES, LCA, and JPL. The orbit differences between our fully combined orbits and the CNES GDR-C orbits are of about 0.8 cm for Jason-1 and at 0.9 cm for Jason-2 in the radial direction. In the cross-track component we observe a clear improvement when adding GPS data to the POD process. The 3D-RMS of the orbit differences reveals a good orbit consistency at 2.7 cm and 2.9 cm for Jason-1 and Jason-2. Our resulting orbit series for both Jason satellites refer to the ITRF2005 reference frame and are provided in sp3 file format on our ftp server.     

激光烧结快速控制系统的研究

介绍了基于PC平台开发的激光烧结快速成形计算机控制系统的总体结构,详述了该系统的硬件结构、软件结构、人机界面等．并讨论了该控制系统硬件结构及软件编制过程中的一些技术细节及特点。     

基于有限元法功能梯度材料零件自适应切片算法

 快速原型制造技术采用分层和材料逐点或逐线堆积加工零件,适合加工每层内或每层间材料有变化的非均质材料零件。分层切片是快速原型制造中非常重要的组成部分,尤其自适应切片是保证零件成型质量和提高快速原型制造效率的有效手段。综合考虑几何信息和材料分布信息,针对基于有限元法的功能梯度材料零件模型几何和材料表达特点,以零件表面外法线,材料变化梯度及材料分辨率为计算层片厚度的依据,对功能梯度材料零件快速原型制造中的自适应切片算法进行了研究。最后给出了分层实例,验证算法的正确性。