挠性充液航天器超近程逼近段动力学建模与控制

超近程逼近过程中,服务航天器为刚柔液耦合的复杂系统,单摆等液体晃动模型不再适用,对这种工况下的航天器进行了动力学建模与控制的研究。采用虚功率原理推导了一种新的适用于三轴推力作用下的液体晃动等效模型,通过引入相对位置导引矢量与相对位置误差矢量,建立了相对轨道误差动力学模型,结合相对姿态动力学模型,得到超近程逼近段的刚柔液耦合的相对轨道姿态动力学模型。针对模型存在的不确定性和未知干扰,设计了基于滑模估计器的相对姿轨耦合控制律。通过数学仿真验证了控制律的有效性,仿真中的晃动结果与Flow-3D结果能够吻合,验证了晃动模型的合理性。     

常值推力下面内轨道优化的一种改进间接法

针对常值推力下航天器面内轨道转移燃耗最省的轨道优化问题,利用极大值原理导出了最优轨迹下推力方向角应满足的控制方程,结合动力学方程建立了一种求解航天器面内最优转移轨道的改进间接法,及其在推力方向角调节能力受限条件下的应用方法。由于避免了协态变量微分方程组的求解,改进间接法相对于传统间接法降低了初值猜测的难度和计算量;与采用Gauss伪谱法求解相比,所建立的改进间接法求解结果精度更高,数值光滑性更好。仿真算例表明:推力方向角调节能力受限会改善推力方向角变化规律,降低推力方向角变化范围;就燃耗而言,推力越大燃耗越多,优化轨道节省燃耗更加显著。     

实际工程中混合模型的任务可靠性分配方法

随着可靠性工程在航空产业中的逐步开展,适合于实际工程中的可靠性分配方法变得日益重要,尤其对于实际工程中混合模型的任务可靠性指标分配来说,因其对应的可靠性模型一般为串、并联等混合的复杂模型,可靠性指标分配相当困难。本文将实际工程中常见的比例组合法和专家评分分配法有效地结合起来,为实际工程中混合模型的任务可靠性分配提供了一种简便易行的方法。     

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SOC的卫星姿轨控系统通用电模拟器设计

在某型卫星地面电联试过程中,对该卫星的姿态轨道控制系统进行接口分析及信号统计,针对其接口复杂性、信号多样性的特点,提出采用片上系统(Systemona Chip,SOC)芯片对所有部件模拟器进行通用化设计。文中给出了该型卫星通用型电模拟器硬件平台设计方案以及陀螺、反作用轮和通用接口模块的硬件配置说明,针对该型卫星姿态轨道控制系统电联试要求,对所有部件按真实接口配置成电模拟器,形成通用接口箱、敏感器电模拟器箱和执行机构电模拟器箱,并通过CAN(Controller Area Network)总线接入闭环仿真,对太阳捕获、地球捕获及正常模式进行了仿真测试,仿真结果表明通用电模拟器满足设计要求,对其他卫星的地面电联试有很好的参考价值。     

Erosion of a Polyimide Material Exposed to Simulated Atomic Oxygen Environment

Oxygen plasma source generated by thermal cathode filament discharge has been used to study the erosion process of polyimide (PI) materials in atomic oxygen (AO) environment, and their mass loss, surface morphology and surface chemical compositions have been examined by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) after exposure to incremental AO flux. The data indicate that the physical adsorption of AO at the samples' surface results in the increase of oxygen concentration when polyimide is exposed to AO flux. Then selective chemical reactions of groups of polyimide materials with AO yield volatile organic compounds, sample mass loss is on linear increase and carpet-like surface morphology forms. In the initial exposure to AO, the reaction occurs mainly between AO and carbon in specific location of aromatic ring, then the reaction rate of C=O groups gradually increases. After AO exposure, the oxygen concentration increases while nitrogen and carbon concentration decreases. Reaction rate of groups containing nitrogen is slower compared with carbon and oxygen.     

径向气体轴承-柔性转子耦合系统动力学研究

采用轨迹法对径向气体轴承(纯动压径向气体轴承、动静混合径向气体轴承)-柔性转子耦合系统的非线性动力学特性进行研究.建立柔性转子系统的多自由度模型,通过变方向隐式(ADI)方法实现瞬态气体润滑雷诺方程(含时间项)与转子动力学方程的耦合求解,通过数值仿真获得了系统在不同偏心质量作用下的非线性气膜力、轨迹图、相图、频谱图、能量谱图、分岔图、振型图及重力作用下轴承的平衡位置分布图.针对所采用的轨迹法的特点,研究了相应的非线性动力学参数获取方法.结果表明,轨迹法能够很好的描述径向气体轴承转子动力学特性及其气膜涡动现象,为径向气体轴承-柔性转子系统设计奠定基础.      

近地卫星编队构形保持方法

针对J2摄动和大气摄动导致低轨编队卫星构型破坏的情况,基于高斯摄动方程给出了以平均轨道根数为被控制量的脉冲控制模型。利用法向脉冲调整轨道倾角和升交点赤经偏差,在轨道上2个位置施加径向和切向脉冲调整其余轨道根数偏差从而修正卫星编队构形。最后通过数值仿真验证了算法的简单性、有效性。     

直接再入大气的月球返回轨道设计研究

直接再入大气的月球返回轨道是月球采样返回任务普遍采用的飞行方案。文章将月-地转移轨道设计与再入大气仿真相结合,通过两级修正策略和落点匹配使月球返回轨道既满足再入界面约束又满足再入点地理位置约束。两条分别采用弹道式和弹道-升力式再入的月球返回轨道的计算结果表明,此方法是有效的。     

嫦娥二号卫星轨道设计

嫦娥二号卫星的轨道设计是在充分继承嫦娥一号轨道设计的理论和方法的基础上进行的,并在此基础上做了适应性改进。轨道设计的主要内容包括参数选择、发射窗口、速度增量需求以及嫦娥二号卫星和嫦娥一号卫星不同点的对比,提出了整个飞行轨道的设计思想。