谈“神舟”号飞船的着陆方式

[题目]"神舟"号飞船返回前飞行在距地面高度h=340 km的圆形轨道上.飞船装有52台发动机,用于姿态控制、变轨机动以及脱轨返回时提供所需要的冲量,为了便于研究,将52台发动机等效为P1、P2、P3、P4四台发动机,如图1所示.开始时,飞船以恒定速度vo=7.7 km/s向x轴正方向运动,要使飞船降低高度返回地面,应当启动哪台发动机?     

"神舟"五号的空间环境保障

空间环境安全保障是载人航天器飞行安全和航天员生命安全保障的一个重要部分．文章从高层大气、高能辐射环境、流星体空间碎片和重大空间环境扰动事件等四个方面空间环境要素对载人航天的影响，介绍了空间环境预报中心为“神舟”五号载人飞行任务所作的空间环境保障工作．     

浅析“神州八号”飞船运行的周期和离心率

利用普通物理学和数学知识,分析“神舟八号”飞船运行的周期,并计算“神舟八号”飞船在预定轨道上运行的离心率．     

“神舟”五号载人飞船的专题课设计

 专题课是物理教学中的一个重要环节,其内容要具备综合性、针对性和新颖性的特点。本文是关于“神舟”五号载人飞船的专题课设计,引导学生利用已学过的牛顿运动定律、圆周运动、能量、动量、光学等基本知识,研究“神舟”五号从发射到着陆整个过程中涉及的有关问题,通过探讨回答这些问题,使学生学会把已有知识再认识、再整合,掌握研究相关或类似问题的思想和方法。录像学习使学生通过多媒体观看“神舟”五号载人飞船发射升空、轨道运行、定点回收的过程,同时阅读“神舟”五号的有关资料,使学生对载人飞船有一定的感性和理性认识。讨论让学生提出与载人飞船有关的物理问题,只需提问,不需回答。     

“神舟”四号中的空间环境研究

空间环境 ,特别是日地空间环境是人类航天活动关系极为密切的环境 .文章以“神舟”四号为背景 ,概要介绍了为“神舟”四号飞船所作的空间环境安全保障服务 ,包括在“神舟”四号飞船上进行的空间环境探测、空间环境分布及变化规律的研究、空间环境对人类航天活动及“神舟”飞船的影响 (空间环境效应 ) ,以及为保障“神舟”飞船发射安全、正常运行、顺利返回所作的空间环境预报等 .此外 ,概要评述了国内外上述研究领域的研究现状与进展     

以"神舟"三号为背景设计的一组跨学科综合试题

1背景材料 我国继1999年11月20日和2001年1月10日成功发射和返回自行研制的"神舟"一号、二号无人试验飞船后,于2002年3月25日22时15分在酒泉卫星发射中心,利用自行设计的"长征二号F"捆绑式大推力运载火箭又成功发射了"神舟"三号无人航天试验飞船,飞船顺利升空,在环绕地球飞行了108圈后,于2002年4月1日下午4时51分,成功着陆在内蒙古中部预定地区.     

“神舟”四号中的微波遥感

多模态微波遥感器是我国第一次进入太空的微波遥感器 ,是一部集高度计、散射计和辐射计为一体 ,具有综合观测能力的微波遥感器 .经过“神舟”四号飞船的在轨运行实验 ,取得了大量的有效科学数据 ,在轨实验获得成功 .文章介绍了多模态微波遥感器的基本工作原理、系统组成和运行控制模式 ,给出了主要技术和应用指标 ,总结了多模态微波遥感器在轨运行情况 ,给出了初步实验结论     

微重力科学进展

微重力科学是研究重力极大地减小的一种极端环境中的流体科学，材料科学，生物科学和技术，以及物理学若干基础问题的新兴学科，近年来，由于地面研究的加强，空间实验的增加以及实验定量化水平的提高，微重力研究取得了很好的进展。     

Length measurement in accelerated systems

We investigate the limitations of length measurements by accelerated observers in Minkowski spacetime brought about via the hypothesis of locality, namely, the assumption that an accelerated observer at each instant is equivalent to an otherwise identical momentarily comoving inertial observer. We find that consistency can be achieved only in a rather limited neighborhood around the observer with linear dimensions that are negligibly small compared to the characteristic acceleration length of the observer.     

富燃料丙烷/空气预混火焰特性的微重力实验研究

地面常重力(1g)条件下,丙烷/空气预混火焰向上传播的富燃极限为9.2%C_3H_8,而向下传播时的富燃极限仅为6.3%C_3H_8,二者之间存在明显差距。利用微重力条件下的实验,对燃料浓度从6.5%到8.6%(微重力实验中测定的可燃极限)范围内的丙烷/空气预混火焰特性进行了研究。实验发现,重力对近极限丙烷/空气火焰的传播有显著影响,影响程度随着当量比的增加而增大。微重力下丙烷/空气的富燃极限为8.6%C_3H_8(φ=2.24),明显高于1g条件下向下传播火焰的可燃极限,略低于向上传播火焰的可燃极限。随着当量比的增大,根据压力变化曲线计算的火焰层流燃烧速度从8.5cm/s逐渐减小到2.7 cm/s,可燃极限处的层流燃烧速度与前人实验数据一致。     

Collective Phenomena in Strongly Coupled Dissipative Systems of Charged Dust: from Ground to Microgravity Experiments

In present work the formation of dusty plasma structures in cryogenic glow dc discharge was investigated. The ordered structures from large number (～10⁴) of charged diamagnetic dust particles in a cusp magnetic trap have been also studied in microgravity conditions. The super high charging (up to 5·10⁷e) of dust macroparticles under direct stimulation by an electron beam is experimentally performed and investigated. The results of the investigation of Brownian motion for strongly coupled dust particles in plasma are presented. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microgravity droplet combustion: effect of tethering fiber on burning rate and flame structure

Droplets tethering on fibers has become a well established technique for conducting droplet combustion experiments in microgravity conditions. The effects of these supporting fibers are frequently assumed to be negligible and are not considered in the experimental analysis or in numerical simulations. In this work, the effect of supporting fibers on the characteristics of microgravity droplet combustion has been investigated numerically; a priori predictions have then been compared with published experimental data. The simulations were conducted using a transient one-dimensional spherosymmetric droplet combustion model, where the effect of the supporting fiber was implicitly taken into account. The model applied staggered convective flux finite volume method combined with high-order implicit time integration. Thermal radiation was evaluated using a statistical narrow band radiation model. Chemical kinetics and thermophysical properties were represented in rigorous detail. Tether fiber diameter, droplet diameter, ambient pressure and oxygen concentration were varied over a range for n-decane droplets in the simulations. The results of the simulations were compared to previously published experiments conducted in the Japan Microgravity Center (JAMIC) 10 second drop tower and the NASA Glenn Research Center (GRC) 5.2 second drop tower. The model reproduces closely nearly all aspects of tethered n-decane droplet burning phenomena, which included droplet burning history, transient and average burning rate, and flame standoff ratio. The predictions show that the presence of the tethering fiber significantly influences the observed burning rate, standoff ratio, and extinction.     

Entropy Generation Analysis of the Flow Boiling in Microgravity Field

Entropy generation analysis of the flow boiling in microgravity field is conducted in this paper. A new entropy generation model based on the flow pattern and the phase change process is developed in this study. The velocity ranges from 1 m/s to 4 m/s, and the heat flux ranges from 10,000 W/m² to 50,000 W/m², so as to investigate their influence on irreversibility during flow boiling in the tunnel. A phase–change model verified by the Stefan problem is employed in this paper to simulate the phase–change process in boiling. The numerical simulations are carried out on ANSYS-FLUENT. The entropy generation produced by the heat transfer, viscous dissipation, turbulent dissipation, and phase change are observed at different working conditions. Moreover, the Be number and a new evaluation number, E_P, are introduced in this paper to investigate the performance of the boiling phenomenon. The following conclusions are obtained: (1) a high local entropy generation will be obtained when only heat conduction in vapor occurs near the hot wall, whereas a low local entropy generation will be obtained when heat conduction in water or evaporation occurs near the hot wall; (2) the entropy generation and the Be number are positively correlated with the heat flux, which indicates that the heat transfer entropy generation becomes the major contributor of the total entropy generation with the increase of the heat flux; (3) the transition of the boiling status shows different trends at different velocities, which affects the irreversibility in the tunnel; (4) the critical heat flux (CHF) is the optimal choice under the comprehensive consideration of the first law and the second law of the thermodynamics.     

落体法测量刚体转动惯量实验中引起测量值偏离的因素分析

测量并分析了落体法测量刚体转动惯量实验中拉绳与转轴的不垂直对刚体转动惯量测量值偏离的影响,得出了转动体系在阻力矩作用下的角加速度与转速的关系.该值偏离的测量与分析可作为刚体转动惯量实验的拓展性、创新性实验内容,有利于启发学生实验思维和培养学生实验创新意识.     

微重力下光滑表面上FC-72的池沸腾实验研究

本文利用小尺度光滑芯片(10 mmxl0 mmx0.5 mm),通过控制加热电流方法,在北京落塔进行了持续3.6 s有效微重力时间的过冷池沸腾实验研究.在低热流和中等热流区,微重力条件下可以观察到稳态或准稳态池沸腾现象,传热特性基本维持不变;在中等热流区域,气泡的横向合并会引起合并后的大气泡表面剧烈震荡,进而引发合并大...     

微重力下微结构表面强化沸腾换热研究

为了提高航天器中电子器件的冷却效率,本文利用干式腐蚀方法形成方柱微结构,通过控制加热电流方法,在北京落塔进行了持续3.6 s有效微重力时间的过冷FC-72池沸腾强化换热实验研究。研究结果表明:相比光滑表面,方柱微结构表面利用其独立于重力水平的毛细作用力,显著地强化了微重力沸腾换热。     

Computations of Dendrites in 3-D and Comparison with Microgravity Experiments

The phase field model is used to compute numerically the temporal evolution of the interface for solidification of a single needle crystal of succinonitrile (SCN) in a three dimensional cylindrical domain with conditions satisfying microgravity experiments. The numerical results for the tip velocity are (i) consistent with the experiments, (ii) compatible with the experimental conclusion that tip velocity does not increase for larger anisotropy (e.g., for pivalic acid), (iii) different for 3D versus 2D by a factor of approximately 1.76, (iv) strongly dependent on physical value of the kinetic coefficient in the model. Also, as indicated by theory and the laboratory experiments, the results obtained for single needle crystal show that the growth velocity approaches a constant value in large time.