Analysis and experiments for delay compensation in attitude control of flexible spacecraft

Space vehicles are often characterized by highly flexible appendages, with low natural frequencies which can generate coupling phenomena during orbital maneuvering. The stability and delay margins of the controlled system are deeply affected by the presence of bodies with different elastic properties, assembled to form a complex multibody system. As a consequence, unstable behavior can arise. In this paper the problem is first faced from a numerical point of view, developing accurate multibody mathematical models, as well as relevant navigation and control algorithms. One of the main causes of instability is identified with the unavoidable presence of time delays in the GNC loop. A strategy to compensate for these delays is elaborated and tested using the simulation tool, and finally validated by means of a free floating platform, replicating the flexible spacecraft attitude dynamics (single axis rotation). The platform is equipped with thrusters commanded according to the on–off modulation of the Linear Quadratic Regulator (LQR) control law. The LQR is based on the estimate of the full state vector, i.e. including both rigid – attitude – and elastic variables, that is possible thanks to the on line measurement of the flexible displacements, realized by processing the images acquired by a dedicated camera. The accurate mathematical model of the system and the rigid and elastic measurements enable a prediction of the state, so that the control is evaluated taking the predicted state relevant to a delayed time into account. Both the simulations and the experimental campaign demonstrate that by compensating in this way the time delay, the instability is eliminated, and the maneuver is performed accurately.     

螺纹滚压对1240MPa级高强钛合金高锁螺栓性能的影响

针对1240MPa级高强钛合金高锁螺栓进行螺纹滚压强化工艺试验研究,结果表明:冷滚压螺纹时,高强钛合金高锁螺栓的螺纹牙顶出现超过0.12mm的折叠,温滚螺纹则没有超标缺陷.1240MPa级高强钛合金高锁螺栓温滚螺纹后的平均抗拉强度比冷滚螺纹的平均抗拉强度低约0.5kN,但高于标准要求20％.冷滚压的螺纹各部位显微硬度稍高于温滚压后的螺纹各部位的显微硬度,冷滚和温滚均使材料得到硬化,适用于高强钛合金高锁螺栓的螺纹滚压工艺为温滚螺纹.     

复合材料结构用紧固件及机械连接技术

先进树脂基复合材料具有的较多优点使其在先进飞机上的使用量越来越大,但是由于材料本身结构特性的原因,使得复合材料结构在连接、装配、使用中易产生一系列问题,针对复合材料的特点及连接和使用中存在的问题,系统地阐述了复合材料结构使用的紧固件用的材料、各种结构用先进紧固件类型以及连接中需解决的具体技术问题。     

复合材料圆筒结构脱层损伤识别研究

针对复合材料圆筒结构,讨论了基于模态柔度曲率矩阵的无损检测方法。通过模态分析获得脱层复合材料圆筒的各阶固有频率及节点振型,计算得到轴向和周向柔度曲率矩阵来判断损伤。研究表明:轴向和周向柔度曲率矩阵两种方法均可达到精确识别脱层位置及大小的效果,且越靠近外筒壁,柔度曲率矩阵图突变越大,越易检测。相对而言,轴向柔度曲率Fc在脱层位置突变远大于周向柔度曲率Fd,更易判断损伤。但当损伤发生在沿轴线固定端边界时,轴向柔度曲率Fc本身就有较小突变,应用周向柔度曲率Fd识别防止误判。     

飞机数字化装配自动钻铆技术及其发展

简述了国外自动钻铆技术发展历程,介绍了我国自动钻铆技术的发展现状,简要分析了自动钻铆技术工艺过程,指出自动钻铆技术在保证飞机制造寿命、提高装配效率等方面的意义;对自动钻铆关键技术组成,如柔性工艺装备技术等进行了概述分析.针对国内飞机自动化装配尚处于起步阶段的现状和大飞机研制生产的需求,提出了我国自动钻铆技术向数字化、柔性化方向集成发展的建议.     

一类完整性控制系统的设计及其在挠性航天器中的应用

本文利用变形Riccati方程的性质,提出一种多变量控制系统设计法。所设计的系统动态特性好,具有最优性,且在执行器失效时具有完整性。文中就挠性航天器动力学控制问题进行了应用研究。     

柔性空间机械臂动力学模型

本文叙述三种柔性空间机械臂的动力学模型,它们的差异在于用不同的方法描述机械臂的弹性变形,即用有限元法、集中参数法和解析法。     

盐雾环境下部段对接紧固件耐腐蚀性研究

海洋盐雾大气环境下,结构直接暴露在大气环境中,可能会遭遇高温、高湿及雨淋等环境条件。通过真实环境浸泡试验和暴露试验,验证在不同防水措施下的不同材料/表面处理的紧固件耐腐蚀性能,并对试验中钛合金螺栓承载力偏低现象进行了分析。     

航空航天用GH2132系列楔形螺纹托板螺母紧固件防松性能研究

针对GH2132材料托板螺母不同规格产品开展楔形螺纹的应用研究,研究了楔形螺纹结构对产品最小安装力矩、反复拆装振动、高低温交变处理环境相容性以及轴向载荷拉脱等性能的影响,找出了楔形螺纹产品安装力矩、预紧力、扭拉系数和振动松脱的关系。研究表明,GH2132材料托板螺母采用楔形螺纹结构的锁紧性能极高,耐反复拆装50次,在温度-196℃~100℃交变环境下松脱力矩不减,抗振动6万次,拉脱力值达到常规自锁产品的1.5倍。     

An analysis of the flexibility modeling of a net for space debris removal

Operational spacecraft are facing a risk of collision with space debris objects. The net capturing method has been proposed to mitigate this risk on spacecraft. The mass-spring model is usually applied for net modeling by discretizing a cable into one or several mass-spring-damper elements in simulation. The absolute nodal coordinates formulation (ANCF) has also been applied to model the net, and this model is able to describe the flexibility of a net using less elements. However, the influence on the net behavior in simulation by the flexibility modeling of a net is not well understood and barely discussed. In this paper, flexibility models of a net are established based on the mass-spring model and the ANCF model,respectively. The influence on the net behavior by the flexibility modeling is, for the first time, analyzed via simulations. Two case studies of capturing a ball and a cube shaped targets are performed. It is found that the flexibility modeling has little influence on the net dynamics in simulation. Finally, the characteristics and benefits of the ANCF model are described and analyzed. A drawback of the ANCF model was found to be its inferior computational performance.