基于自适应滑模方法的航天器位置与姿态控制

为了解决存在参数不确定和外干扰的航天器位置与姿态控制问题,提出一种自适应滑模控制方法.该方法用于控制航天器的位置和姿态,确保航天器执行位置与大角度机动,完成捕获和移除大空间目标的任务.提出的控制算法无需不确定的界,比传统的滑模方法容易实现.Lapunov分析表明,设计的控制器保证了位置与姿态的渐近跟踪.最后,将该方法用于航天器的位置与姿态控制,仿真结果验证了方法的有效性.     

The influence of grain geometry and wear conditions on the material removal mechanism in silicon carbide grinding with single grain

High efficiency and precision grinding of brittle materials is challenging due to material physical and chemical properties. To understand the effect of grain geometry and wear conditions on the material removal mechanism in brittle material precision grinding, a single diamond grain grinding experiment was conducted on Silicon Carbide (SiC). The cutting edge radius and deflection angle were measured by confocal scanning. Under six different cutting edge radius and three maximum undeformed chip thickness, grinding force and ground surface were measured. Diamond grain wear was investigated by observing the grain morphology, wear rate, grinding force, and ground surface change over accumulative material removal volume. The result showed the existence of a critical cutting edge radius for improving SiC ground surface quality.. Normal grinding force increased with the cutting edge radius increase. Tangential grinding force increased with the cutting edge radius increase and reached the peak value at the critical cutting edge radius. Flank wear was the major wear mode in precision SiC grinding. The grain wear was associated with the grinding force and ground surface.     

532 nm nanosecond pulse laser triggered synthesis of ZnO2 nanoparticles via a fast ablation technique in liquid and their photocatalytic performance

Cubic phase zinc peroxide nanoparticles (ZnO₂ NPs) with an average diameter of ca. 9–15 nm have been synthesized via a fast nanosecond pulse laser ablation in liquid technique (PLAL), using H₂O₂ aqueous solution as the ablation media and a 532 nm pulsed laser as the irradiation source and low-cost zinc powder as the solid target. Both the laser energy and ablation time potentially have a substantial influence on the formation of ZnO₂ NPs. Due to its relatively high oxidation level as well as its hydrophilic wetting behavior, the as-synthesized ZnO₂ NPs exhibit efficient photocatalytic degradation ability of Rhodamine B (RB) whilst remaining stable to photodegradation. The possible mechanisms of the photocatalytic behavior have been discussed in what follows.     

基于激光雷达的航天器相对位姿测量技术

基于激光雷达的航天器相对位姿测量技术已成为故障航天器在轨捕获与维修、空间垃圾清除等空间操控活动开展必不可少的关键技术之一。针对这一技术,阐述了国内外研究现状;然后,描述了相对位姿测量技术原理,并重点介绍了点云配准方法;最后,进行了航天器模拟器的相对位姿测量精度仿真验证。结果表明:基于激光雷达的航天器相对位姿测量技术方法合理可行,测量精度高,可满足近距离操控中相对导航任务需求,对国内后续开展工程应具有较大参考价值。     

基于激光成像雷达的空间非合作目标相对导航技术

激光成像雷达具有工作距离长、工作频率高、波束窄,距离和角度测量精度高,受光照条件影响小等诸多优势,在空间应用上的需求越来越迫切。主要介绍了国内外激光成像雷达在轨应用现状,并介绍了基于激光成像雷达的空间非合作目标相对导航的主要关键技术,包括应用激光成像雷达的相对位姿测量技术和相对导航滤波技术,最后给出了应用激光成像雷达的相对位姿测量仿真结果。仿真实验结果表明:基于激光成像雷达的非合作目标相对导航技术具有受空间环境影响小、测量精度高的优势,方案合理可行,满足空间非合作目标相对导航任务需求,可应用于近距离空间目标的在轨维护与服务和空间操控,为我国后续开展相关工程应用提供技术参考。     

多环闭链可展机构尺寸调整方法

由于存在加工误差等因素,可展机构各连杆实际加工长度与理论计算长度往往不同,需要在装配时对其调整。多环闭链可展机构具有闭环多、环约束互相耦合、参数关系复杂等特点。为解决在尺寸调整时存在的高非线性、强耦合等问题,以均方根形式定义多环闭链机构的综合调整量,并以调整结构势能最小作为目标函数,推导出多环闭链可展机构尺寸调整的基本数学模型。根据实际调整方式,提出单向调整和双向调整两种计算模型。在此基础上,对多构态下多环闭链可展机构的尺寸调整方法进行研究。通过算例对上述方法和模型进行验证。结果表明,利用该方法得到的调整结果能满足可展机构多构态、多约束、多种调整方式的要求。研究成果有助于降低多环闭链可展机构的装配和加工难度。     

基于无监督域适应的仿真辅助SAR目标分类方法及模型可解释性分析

卷积神经网络(CNN)在光学图像分类领域中得到广泛应用,然而,合成孔径雷达(SAR)图像样本标注难度大、成本高,难以获取满足CNN训练所需的样本数量.随着SAR仿真技术的发展,生成大量带标签的仿真SAR图像并不困难.然而仿真SAR图像样本与真实样本间难免存在差异,往往难以直接支撑实际样本的分类任务.为此,该文提出了一种...     

Cryogenic Orbital Testbed (CRYOTE) development status

High-performance space travel is enabled with propellants having a high specific impulse, and the highest specific impulse can be produced with hydrogen. The Cryogenic Orbital Testbed (CRYOTE) provides an in-space environment where the unique properties and fluid flow of hydrogen can be demonstrated in micro- or zero-gravity. With partnerships across industry and NASA, CRYOTE has developed a detailed concept of an in-flight core system (that can accommodate a variety of experiments). Development has included launch vehicle interface development for transfer of residual Liquid Hydrogen (LH2) from the launch vehicle to a development tank and an in-depth thermal analysis considering the orbital thermal environment and heat loads imparted on the thermal system.This paper will describe the non-proprietary development to date, outline lessons learned in the development, and detail the plan moving forward with the CRYOTE project.     

Concept for on orbit liquid hydrogen test bed

There is growing interest in the utilization of cryogenic propellants for future space missions. The utilization of these propellants for long duration in space presents substantial challenges in fluid management in the low g environment. Lockheed Martin (LM) is developing the concept for a space borne system for demonstration of long term storage, various fluid management tests involving control of tank pressure, location and identification of vapor and liquid phases, venting in low g, mass gauging, and extension of life with cryocoolers and location of liquid for transfer. In addition the concept includes autonomous coupling and hydrogen transfer from tank to tank. The concept is based on a flight qualified flight proven hydrogen Dewar design from a previous program The concept for this system is described.     

真空多层绝热性能测试装置及初步实验验证

建立了一套低温用真空多层绝热材料性能测试装置,用于研究变密度多层绝热材料的特性规律。以内密外疏的层密度分布方式为例,在测试装置充注液氮之后,通过稳态量热法实验研究了真空条件下该布置方式绝热层内不同层位置的温度瞬态和稳态分布规律、单点的降温规律、以及单位面积漏热率情况。考察了稳态温度分布以及单位面积热流随热边界温度的变化特性,并将理论温度分布曲线与实验曲线进行了对比,从而验证层与层模型的准确性。