21世纪的航天(续)

航天事业在20世纪已取得显著进展和辉煌成就。21世纪即将来临。在21世纪,世界航天如何发展、将取得哪些重大成就,是人们关注的话题。为此,笔者根据有关材料汇编了这份材料,以供参考。共4讲,第一、二讲已刊登在本刊1998年第4期,下面为第三、四讲。     

着陆小行星的滑模变结构控制

针对由于目标小行星的各种物理参数和运动信息不能精确获取而导致着陆小行星的动力学方程中存在不确定项这一问题，设计了一种基于滑模变结构的软着陆小行星的制导控制方案。在考虑安全软着陆约束条件下规划了标称着陆轨迹；通过滑模变结构控制方法设计制导控制律，实现对理想标称轨迹的鲁棒跟踪，从而保证成功着陆小行星；最后通过计算机仿真验证了方案的可行性。     

Human exploration of near earth asteroids: Mission analysis for chemical and electric propulsion

This paper presents a mission analysis comparison of human missions to asteroids using two distinct architectures. The objective is to determine if either architecture can reduce launch mass with respect to the other, while not sacrificing other performance metrics such as mission duration. One architecture relies on chemical propulsion, the traditional workhorse of space exploration. The second combines chemical and electric propulsion into a hybrid architecture that attempts to utilize the strengths of each, namely the short flight times of chemical propulsion and the propellant efficiency of electric propulsion. The architectures are thoroughly detailed, and accessibility of the known asteroid population is determined for both. The most accessible asteroids are discussed in detail. Aspects such as mission abort scenarios and vehicle reusability are also discussed. Ultimately, it is determined that launch mass can be greatly reduced with the hybrid architecture, without a notable increase in mission duration. This demonstrates that significant performance improvements can be introduced to the next step of human space exploration with realistic electric propulsion system capabilities. This leads to immediate cost savings for human exploration and simultaneously opens a path of technology development that leads to technologies enabling access to even further destinations in the future.     

激光雷达对沉潜油探测的探索*

目前,人们对于海洋沉潜油的规律研究及控制水平较低,特别是探测30m深度以内的浅海地区的沉潜油分布信息,其主要原因是缺乏快速有效的探测手段。北京遥测技术研究所开发水下探测激光雷达样机,利用激光在海水中良好的透过特性,用于对水下沉潜油的探测以及对海底等目标的高精度探测。样机完成在水池中进行水下沉潜油的模拟探测试验,对沉潜油样本的典型激光回波信号进行采集分析,并测量模拟探测深度。试验结果基本符合设计预期,为进一步提升激光雷达沉潜油探测能力打下良好基础。     

动态数据录取系统在水下武器试验中的应用研究

介绍了在水下武器试验中动态数据录取系统的工作原理 ,并对录取过程中出现的异常值进行了深入的分析 ,提出了几种异常值合理剔除和取代的方法 ,最后通过试验中的应用来证明这些方法的有效性。     

数学教学中培养创造能力的探索

本文结合多年教学实践，对激发学生的创造意识，培养发散思维，运用创造技法等方面进行了探索。     

面向小行星微重力环境探测的自恢复直立弹跳机器人设计

针对小行星微重力环境,提出了一种具有蛋形外壳,利用弹簧蓄力的并联腿弹跳机器人。该机器人无论以何种姿态落地,均可在重力矩作用下恢复直立姿态。这一设计相对于需要额外主动装置恢复直立的先前方案,节省了恢复直立所需的能耗,在结构上更为简单可靠。文中阐述了完整的机构设计方案,及相应的结构参数优化计算方法。通过的样机实验,设计方法的有效性得到验证。     

我国太阳能应用的可行性分析

本文针对我国推广使用绿色环保能源太阳能的可行性进行了探讨，文章首先介绍了太阳能的产生机制，分析了我国太阳能资源的能量总量和分布情况，讨论了直接利用太阳能的二种途径：光热转换和光电转换，并具体讨论了光热转换和光电转换所涉及的实际技术，具体包括：用于采集太阳能并进行光热转换的集热器、辅助热动力系统、太阳能供暖、太阳能制冷、太阳能热力发电、太阳光发电，介绍了国内外使用太阳能的现状和发展趋势，并对我国地域广大且太阳能资源丰富的西部地区的太阳能开发利用的可行性进行了分析。     

基于SAR子孔径图像的浅海水下地形探测

沿海地区水下地形的精确测量是人类开展海洋活动的关键,合成孔径雷达（SAR）为浅海地形的探测提供了一种新的手段,其中TerraSAR-X 的聚束模式以较长的积分时间得到高分辨率的 SAR 数据,从而能较为精确地反演浅海的海底地形。传统 SAR 图像水下地形探测基于波周期不变的假设,这不仅需要已知初始水深求解波周期,还给探测结果带来一定误差。本文提出一种基于子孔径图像的水下地形探测方法,将一景SAR图像分解成多景时间间隔固定的子孔径图像,利用子孔径图像间的时间间隔,求解不断变化的波周期,从而获得更加精确的水下地形。使用在海南蜈支洲岛的 TerraSAR-X 数据验证了此方法的可行性,将此方法反演得到的结果与GEBCO数据进行比较,发现两者吻合较好（MAE为2.8 m,MRE为23.91%）,证明了此方法在浅海反演水深的巨大潜力。     

Contributions of the International Space Station towards future exploration missions

When the idea of a large space station in Low Earth Orbit (LEO) was conceived in the 1980s, it was primarily planned as an orbiting laboratory for microgravity research. Some even thought of it as an industrial plant in space. Whereas the latter did not materialize because of various reasons, the former is absolutely true when you talk about the International Space Station (ISS). Since the transition to a six astronaut crew in 2009 and the completion of its assembly in 2011, it has been intensively used as laboratory in a wide field of scientific topics. Experiments conducted on ISS have yielded first class results in biology, physiology, material science, basic physics, and many more. While its role as a laboratory in space is widely recognized, the awareness for its potential for preparing future exploration missions beyond LEO is just increasing. This paper provides information on how the ISS programme contributes to future exploration efforts, both manned and unmanned. It highlights the work that has been done or is currently underway in the fields of technology, operations, and science. Further potentials and future projects for exploration preparation are also shown. A special focus lies on experiments and projects primarily funded by the German Aerospace Center (DLR) or with strong German participation in the science team.     

水下航行体减阻技术综述

空/水跨介质飞行器经空中飞抵目标水域后高速入水,对目标实施快速打击,具有隐蔽性好、突防能力强等特点。但在水下航行中,固/液界面阻力及绕流流场变化等问题严重影响了航行速度与稳定性。减小航行体表面阻力干扰、流场优化是保障水下高速稳定航行的关键。旨在探讨适用于水下高速航行体的表面减阻与流场优化方法,对表面微结构减阻、超疏水表面减阻、超空泡减阻和微气泡减阻4种最具代表性的固/液界面减阻技术进行论述,分析各种减阻技术的机理与应用可行性,探讨适用于水下高速航行体的减阻技术发展方向。     

不同喷气结构对航行体高速入水冲击的影响研究

开展了不同头部喷气结构对高速入水航行体降载作用影响的数值模拟研究。结果表明,对于不同等直径喷嘴,相同喷气量下航行体入水空泡形态及压力分布发展过程接近,降载效果基本相同。与无喷气时相比,最大入水最大冲击力和压力可分别降低92%和98%。收缩型喷嘴形成的附体空泡保护层明显小于等直径方案,降载效果削弱。喷嘴扩张较小时头部喷气降载和减阻效果略低于等直径方案,随喷嘴出口扩张比增大,其效果降低。     

Fostering links between environmental and space exploration: the Earth and Space Foundation

The links between Earth and space exploration occur across a broad spectrum, from the use of satellite technology to support environmental monitoring and habitat protection to the study of extreme environments on Earth to prepare for the exploration of other planets. Taking the view that Earth and space exploration are part of a mutually beneficial continuum is in contrast to the more traditionally segregated view of these areas of activity. In its most polarized manifestation, space exploration is regarded as a waste of money, distracting from solving problems here at home, while environmental research is seen to be introspective, distracting from expansive visions of exploring the frontier of space. The Earth and Space Foundation was established in 1994 to help further mutually beneficial links by funding innovative field projects around the world that work at the broad interface between environmental and space sciences, thus encouraging the two communities to work together to solve the challenges facing society. This paper describes the work of the foundation and the philosophy behind its programmes.