A multiple-rendezvous,sample-return mission to two near-Earth asteroids

We propose a dual-rendezvous mission, targeting near-Earth asteroids, including sample-return. The mission, Asteroid Sampling Mission (ASM), consists of two parts: (i) flyby and remote sensing of a Q-type asteroid, and (ii) sampling of a V-type asteroid. The targeted undifferentiated Q-type are found mainly in the near-Earth space, and to this date have not been the target of a space mission. We have chosen, for our sampling target, an asteroid from the basaltic class (V-type), as asteroids in this class exhibit spectral signatures that resemble those of the well-studied Howardite–Eucrite–Diogenite (HED) meteorite suite. With this mission, we expect to answer specific questions about the links between differentiated meteorites and asteroids, as well as gain further insight into the broader issues of early Solar System (SS) evolution and the formation of terrestrial planets. To achieve the mission, we designed a spacecraft with a dry mass of less than 3 tonnes that uses electric propulsion with a solar-electric power supply of 15 kW at 1 Astronomical Unit (AU). The mission includes a series of remote sensing instruments, envisages landing of the whole spacecraft on the sampling target, and employs an innovative sampling mechanism. Launch is foreseen to occur in 2018, as the designed timetable, and the mission would last about 10 years, bringing back a 150 g subsurface sample within a small re-entry capsule. This paper is a work presented at the 2008 Summer School Alpbach,“Sample return from the Moon, asteroids and comets” organized by the Aeronautics and Space Agency of the Austrian Research Promotion Agency. It is co-sponsored by ESA and the national space authorities of its Member and Co-operating States, with the support of the International Space Science Institute and Austrospace.     

大厚度复合材料制件(内埋金属)的超声检测分析

采用超声波无损检测及金相试验方法研究了内埋金属件的大厚度复合材料实心部位的微观结构,发现采取0o纤维在金属件周围进行缠绕铺层时容易引起超声波的衰减,分析了超声波衰减的机理,首先预浸料中夹杂微小气泡引起孔隙率较低,形成了复合材料内部的疏松缺陷;其次由固化过程时内应力引起的微裂纹,导致超声波信号发生衰减;另外,纤维屈曲或局部树脂分布不均匀对超声波也有一定影响。     

超声波智能料位遥测系统

介绍了无线遥控式超声波智能料位测量系统的工作原理。该系统具有测量精度高，速度快，重复误差小的特点，并有数据运算与记忆功能。     

超声波流量计的全数字式准确计时方法

本文详细讨论了超声波流量计的测量与计时原理,采用两组高频脉冲序列计数以提高计时电路的分辨率,并通过电路实验测定了两组脉冲频率分别为2.1MHz和1.93MHz时,计时电路分辨率的大小。实验结果与理论计算完全相符。最后提出了一种新型的功能性强的超声波流量计实施方案。     

螺栓轴向紧固力的超声测量

叙述了超声波与螺栓应力之间的理论关系及基实验证明。以此为基础制成的仪器可直接测出螺栓的轴向紧固力。在大量采用螺给作为紧固件的航天领域，该项技术可保障各类火箭及其他构件的工作可靠性。     

超声波喷嘴试验研究

对超声波喷嘴的工作原理及工作特性进行了理论分析和试验研究,利用计算机图象处理技术重点研究了压电器件材料物性参数d33、激励电压A、喷射压力p、喷孔直径d0、喷嘴腔纵向尺寸δ及激励频率f对射流液滴形成的影响。研究表明：较低的射流压力和较小的喷孔直径以及较大的d33压电器件都有利于液滴的形成和工作稳定性,而激励频率f和喷嘴腔纵向距离δ都存在着最佳值。这些结论可以指导喷印机超声波喷嘴的设计。     

基于超声波在污水流量测量中的应用研究

针对工业污水流量的测量问题,提出一种基于超声波的污水流量测量方法。通过对污水流量的测量原理的分析,设计出以单片机AT89C2051为核心的流量测量系统。实践表明,该测量系统具有高集成度、反应速度快,测量准确度高等特点。     

超声辅助等离子体中微细电火花加工技术研究

冷等离子体射流中微细电火花加工在一定程度上获得了比纯气体介质中更好的加工性能。然而由于放电脉冲能量小,造成放电间隙小,使得电蚀产物排出困难,短路、拉弧等不正常放电现象仍然频繁发生,严重影响了加工的质量和稳定性。为此,提出在工件上施加超声振动的方法以改善冷等离子体射流中微细电火花加工过程的稳定性,并探究其加工特性。针对电火花加工的击穿距离、材料去除率、表面粗糙度以及工具电极相对损耗率等工艺指标,进行了工艺试验。试验结果表明:工件施加超声振动以后,熔融的电蚀产物更容易从工件表面剥离;当以冷等离子体和压缩空气混合射流为加工介质时,超声辅助等离子体中微细电火花加工性能得以明显改善,材料去除率提高13%,表面粗糙度降低19%,电极相对损耗率降低13%。     

点焊接头超声C扫描图像分析及焊核直径测量

采用超声波扫描显微镜获取了点焊接头C扫描图像,分析点焊接头C扫描图像灰度值的分布特征,提出了一种对焊核边缘、焊核直径进行快速检测分析的方法;对不同焊接工艺参数下的不锈钢点焊接头进行表面检测,对比分析基于C扫描图像的焊点检测结果与实际测量值。结果表明,通过这种测量方法不但可以快速得到焊核边缘及焊核尺寸,而且避免了人为因素的影响;与实际测量结果相对比,两者之间相差较小,证实了该检测方法的可行性。