椭圆轨道卫星编队飞行的最优控制研究

研究了椭圆轨道卫星编队飞行的队形保持问题,设计了李雅普诺夫(Lyapunov)控制律,并用遗传算法对控制律进行了优化。为克服遗传算法局部寻优能力差的缺点,对遗传算法进行了改进,设计了自适应模拟退火遗传算法。仿真结果表明,采用Lyapunov方法进行队形保持能提高位置保持的精度,且在经过遗传算法优化后,所消耗的燃料基本与线性二次型(LQR)方法一致;同时,减少了计算时间,有利于星上计算机的实现。     

基于多传感器的卫星自主导航信息融合算法

通常卫星上装有较多的自主导航传感器,如何将其信息有效的组织并充分利用,是卫星自主导航的关键问题。采用信息融合技术把两种或多种导航系统组合起来,应用最优估计理论,形成最优组合导航系统,有利于充分运用各导航系统的信息进行信息互补和信息合作,已逐渐成为了导航定位技术的发展方向。文章针对星敏感器、红外地平仪、雷达高度计、紫外敏感器组成的卫星自主导航系统的特点,提出了一种基于联邦卡尔曼滤波技术进行轨道确定的信息融合算法。仿真结果表明,该方案能够获得较高的定轨精度,有效抑制滤波发散,整个系统的运算速度和收敛速度也有所提高。     

相干干扰对基于特征空间分解算法性能的影响

分析干扰信号的互相关性和方向矢量正交性对接收信号自相关矩阵的特征值和特征向量分布的影响。干扰相关时,会有信号特征矢量发散到噪声空间,采用基于特征空间分解的自适应算法,只有在相干干扰的来向相同时才能实现干扰抑制,否则不能抑制此相干干扰;干扰不相关时,如果干扰来向相同,只能检测到一个干扰,但此时基于特征空间分解的自适应算法可实现干扰抑制。对MUSIC(multiple signal classification)和最小范数算法的仿真结果,与理论推导一致。     

基于双观测器的卫星姿控系统敏感器故障隔离

卫星的姿态测量部件通常包括光学敏感器和惯性敏感器,这两类敏感器的故障隔离是卫星闭环姿控系统故障诊断的难点之一。利用双观测器方法实现两类敏感器的故障隔离,由卫星姿态运动学方程可知,这两类敏感器的输出存在解析冗余,可建立一个"虚拟"系统。对这个系统设计两个不同的观测器,其中一个是Kalman滤波器,能检测两类敏感器的故障;另一个是隔离观测器,能检测光学敏感器的故障,通过比较这两个观测器的输出残差,达到故障隔离的目的。将该方法应用于包含太阳敏感器、红外地球敏感器和陀螺的卫星姿控系统的故障诊断,数学仿真结果验证了这种方法的有效性。     

反作用轮不完全数据故障诊断新算法

针对卫星反作用轮遥测数据存在不完备情况,提出一种基于核模糊均值聚类（KernelFuzzy C-Means,KFCM）的数据修复诊断算法KFCM-Imputation(KFCM-I)。该算法通过KFCM聚类实现已知故障样本的聚类中心和聚类半径,通过相似度计算查找与不完备数据最相似的数据点,将该数据点填充于不完备数据点位置,保证数据的完备性,并通过数据的相似度进行故障诊断。考虑所有故障特征同步缺失数据和各故障特征随机缺失数据两种工况,对比工程上直接删除缺失数据的方法,在数据缺失量小于总数据量的13%时,KFCM-I诊断精度能达90%以上;当数据缺失量占总数据量13%～20%时,诊断精度仍能达到80%。KFCM-I算法故障诊断精度高、计算简单,对工程应用有较好的参考价值。     

GEO SAR长合成孔径时间弯曲轨迹成像试验

地球同步轨道合成孔径雷达（GEO SAR）具有重访周期短,观测范围广等优点,在军事及民用领域具有重要的应用价值。针对GEO SAR长合成孔径时间弯曲轨迹复杂成像特性,首次提出一种地面演示验证方法,对长合成孔径时间弯曲轨迹下成像可行性进行验证。给出长合成孔径时间弯曲轨迹定量分析过程,提出具体试验方案,最后角反射器成像品质评估结果表明可实现长合成孔径时间弯曲轨迹下目标点成像。     

基于卫星在轨温度预示热控涂层性能退化的方法

介绍了一种利用卫星在轨温度数据预示热控涂层在轨性能退化情况的方法,建立并推导了适用于研究热控涂层随整数年变化规律的数学模型,该模型利用卫星设备的温度曲线通过反演计算得到设备表面热控涂层的退化数据。为检验本文数学模型的计算效果,构造了一组数值试验,结果表明本文数学模型的计算数据与真实值非常接近,说明本文建立的数学模型能够很好地根据卫星在轨温度计算出热控涂层在轨退化数据。     

Numerical orbit integration based on Lie series with use of parallel computing techniques

This article outlines necessary steps to perform numerical orbit integrations based on a Lie series approach. Its implementation requires an efficient evaluation of resulting series coefficients. As an example we treat the classical main problem in satellite orbit calculation (_J2$J_2$ only) and the case of a 4×4$4\times 4$-gravity field. All calculations were performed in very high precision with up to 100 significant digits. In comparison to independent third party computations this approach led to superior results referring to the verifiable constancy of various integrals of motion. To achieve a performance similar to classical numerical integrations in terms of acceptable computing time, at least for non-Keplerian motion problems, we exploited parallel computing capabilities. For our examples, run times were improved by several orders of magnitude, depending on the actual chosen precision level (up to a factor of 50,000 in case of double precision). Here we present the mathematical framework of the proposed orbital integration scheme as well as the work flow for its application in a multi-core, parallel computing environment.     

Severe disruption of the cytoskeleton and immunologically relevant surface molecules in a human macrophageal cell line in microgravity—Results of an in vitro experiment on board of the Shenzhou-8 space mission

During spaceflight the immune system is one of the most affected systems of the human body. During the SIMBOX (Science in Microgravity Box) mission on Shenzhou-8, we investigated microgravity-associated long-term alterations in macrophageal cells, the most important effector cells of the immune system. We analyzed the effect of long-term microgravity on the cytoskeleton and immunologically relevant surface molecules. Human U937 cells were differentiated into a macrophageal phenotype and exposed to microgravity or 1g on a reference centrifuge on-orbit for 5 days. After on-orbit fixation, the samples were analyzed with immunocytochemical staining and confocal microscopy after landing. The unmanned Shenzhou-8 spacecraft was launched on board a Long March 2F (CZ-2F) rocket from the Jiuquan Satellite Launch Center (JSLC) and landed after a 17-day-mission. We found a severely disturbed actin cytoskeleton, disorganized tubulin and distinctly reduced expression of CD18, CD36 and MHC-II after the 5 days in microgravity. The disturbed cytoskeleton, the loss of surface receptors for bacteria recognition, the activation of T lymphocytes, the loss of an important scavenger receptor and of antigen-presenting molecules could represent a dysfunctional macrophage phenotype. This phenotype in microgravity would be not capable of migrating or recognizing and attacking pathogens, and it would no longer activate the specific immune system, which could be investigated in functional assays. Obviously, the results have to be interpreted with caution as the model system has some limitations and due to numerous technical and biological restrictions (e.g. 23 °C and no CO₂ supply during in-flight incubation). All parameter were carefully pre-tested on ground. Therefore, the experiment could be adapted to the experimental conditions available on Shenzhou-8.     

Optimal H∞ robust output feedback control for satellite formation in arbitrary elliptical reference orbits

A two degree-of-freedom signal-based optimal H_∞ robust output feedback controller is designed for satellite formation in an arbitrary elliptical reference orbit. Based on high-fidelity linearized dynamics of relative motion, uncertainties introduced by non-zero eccentricity and gravitational J2 perturbation are separated to construct a robust control model. Furthermore, a distributed robust control model is derived by modifying the perturbed robust control model of each satellite with the eigenvalues of the Laplacian matrix of the communication graph, which represent uncertainty in the communication topology. A signal-based optimal H_∞ robust controller is then designed primarily. Considering that the uncertainties involved in the distributed robust control model have a completely diagonal structure, the corresponding analyses are made through structured singular value theory to reduce the conservativeness. Based on simulation results, further designs including increasing the degrees of freedom of the controller, modifying the performance and control weighted functions, adding a post high-pass filter according to the dynamic characteristics, and reducing the control model are made to improve the control performance. Nonlinear simulations demonstrate that the resultant optimal H_∞ robust output feedback controller satisfies the robust performance requirements under uncertainties caused by non-zero eccentricity, J2 perturbation, and varying communication topology, and that 5 m accuracy in terms of stable desired formation configuration can be achieved by the presented optimal H_∞ robust controller. In addition to considering the widely discussed uncertainties caused by the orbit of each satellite in a formation, the optimal H_∞ robust output feedback control model presented in the current work considers the uncertainties caused by varying communication topology in the satellite formation that works in a cooperative way. Other new improvements include adopting a new method to more accurately describe and analyze the effects of the higher-order J2 perturbation, combining all the uncertainties into a diagonal structure, and utilizing a structured singular value to synthesize and analyze the controller.