A NASA Engineer Explains How You Give Directions in Space How do you give directions in space? : originally appeared on Quora : The best answer to any question. Ask a question, get a great answer. Learn from experts and access insider knowledge. You can follow Quora on Twitter , Facebook , and Google+ . Navigation requires a reference frame. We need reference frames to tell us where we are with respect to other objects and we need reference frames to tell us how we are oriented with respect to other objects. There is no single universal frame that is used for all operations. Typically, the reference frame that most simplifies the mathematics and visualization is used for a particular objective. For example, just for the International Space Station (ISS), we use more than 15 reference frames. There is a reference frame that is helpful for pinpointing a location within the ISS. It is Cartesian and gives locations with respect to forward and aft, starboard and port, overhead and deck. Another frame is used for structural calculations and gives ISS hardware locations in terms of X, Y, and Z. But since that body frame is with respect to the center of mass of the ISS, it doesn't really help us understand the orientation of the vehicle, so we need an additional frame for that, one that can take that X, Y, Z body frame and describe it as rotations about the local vertical and local horizontal. And, although that frame (LVLH) is great for telling us the vehicle attitude, it isn't helpful for telling us the vehicle location. We need a frame for that, too. Most commonly we use a frame called J2000 to describe the location of the vehicle. J2000 has its origin at the center of the Earth. As the ISS moves forward in its orbit and as its altitude changes because of either decay or thruster burns, J2000 can provide a precise understanding of the ISS location with respect to the Earth, below. It gets a bit more complicated, though. Individual systems and sensors often use their own frames and then the software converts from one to another. For example, GPS provides the ISS location in the CTRS (Conventional Terrestrial Reference System) and the software converts that to J2000 for use by the vehicle GNC software and by the flight controllers. But, now we're getting to the heart of your question. What happens when a spacecraft is no longer in Earth orbit? How do we define its location, then? The answer is to identify the primary body that the vehicle is respondent to. For spacecraft traveling throughout the solar system, the ideal reference frame is one centered on the Sun. But, once the spacecraft is close to its destination (e.g. Saturn), it would make sense to also begin to report coordinates with respect to that body. And what about when we leave the solar system? Well, we haven't really done that yet. Although Voyager has technically left the solar system, it still makes sense to describe its location with respect to the Sun. As we move far beyond the Sun, we would need to look for a frame that optimizes the situation. It might make sense to use a frame that is centered on the center of our galaxy, because our Sun, the spacecraft, and whatever star we are going to visit will all be in orbit about the center of the galaxy. But, currently we care about how things are located with respect to our solar system. For that, a frame called ICRS (International Celestial Reference System) is commonly used. It is a quasi-inertial frame centered on the barycenter of our solar system. It is maintained by tracking the positions of almost three hundred sources outside our galaxy (e.g. quasars). While coordinates of a frame like J2000 are given in cartesian X, Y, Z, a frame like ICRS uses the spherical coordinate system of Right Ascension, Declination, and Distance.
Use DiskPart on Windows OS to recover unallocated space on SD card for Raspberry PI Press Windows-R and type DiskPart in the ‘Open’ box. Type:‘list disk’ and look for the disk that resembles your SD card. (For this tutorial, assume it’s disk 1) Type ‘select disk 1′ Type ‘clean’. This resets the disk. Type ‘create partition primary’ Type ‘exit’ to quit.
Description of the Research Plan Title: A novel situated social-personalized learning approach Keywords: e-learning, personalized learning, knowledge space construction, situatedknowledge representation, learning path analysis, cognitive learning process, ande-learning assistant agent Objectives: This research program is to develop an intelligent E-LearningAssistant (ELA) agent for personalized learning. A novel situated social-personalizedlearning approach is proposed in this proposal. This research plan covers threeaspects: The first one is to develop a situated knowledge representation andorganization (SKRO) model. The second is to research nonlinear personallearning path or behavior model. The third is to research social-personalizedlearning mechanism based on machine learning algorithms. The details of thesethree aspects are as follows: 1. Research on situated knowledge representation and organization model Knowledge representationand organization method is the fundamental element for building an e-learningsystem. Here, enlightened by the belief of cognitive learning and pedagogy, i.e.“knowledge is situated and learning is also situated”. A situated knowledgerepresentation and organization (SKRO) model is proposed for building asituated e-learning environment. The SKRO model not only can construct acontextual relationship of knowledge, but also can build a map of differentkinds of heterogeneous knowledge (e.g. text, audio, video, animation, imagesand others). The SKRO model is also a modeling foundation of personal learningprocess and how they learn. 2. Research on nonlinear personal learning path or behavior model With the SKRO model, the concept ofconstructive memory is proposed for storing learning content about thelearners’ situations, goals, and learned knowledge. More important, all theselearned knowledge will be recorded according to a time series and a specificsequence of learning activities. An individual learning path (actually shouldbe a map, not a path) is modeled here to record his learning process andcognitive process. At last, the personal learning space (PLS) is constructedwith personal learned knowledge and nonlinear learning path/behavior. 3. The social-personalized learning mechanism based on machine learningalgorithms The thirdresearch highlight is that we hold a belief that one’s learning process andcognitive process may be helpful to others. Therefore, a novelsocial-personalized learning mechanism based on machine learning algorithms isproposed for personalized learning. The social-personalized learning mechanismmeans that intelligent ELA agent can sense social learning processes (i.e. eachlearner’s sequence of learning activities in any order) to analyze therelevance of knowledge. After that, it constructs a situated knowledgerelevance model through employing statistic-based machine learning algorithms. Sucha model can tell one learner what others’ learning process are and how theylearn through analyzing personal and social learning path. At the same time, thesocial-personalized learning mechanism can also tell the learner what knowledgeI should learn now according to his situation and goals. The framework of intelligent E-Learning Assistant(ELA) agent is as following:
My girlfriend sent me an eBook, and I feel obligated to read it. Just now, I saw in the book: Have an ice weekend! I was puzzled: What? Then, I started to laugh. You, too
最近参加了几次有关人类载人航天的学术会议，在会上，大家提出，在空间弱磁场，特别是微重力的作用下，空间乘员发骨骼脱钙、肌肉萎缩、肌肉力量减弱、操作正确性降低、记忆力下降等现象，这些现象采用什么“概念”来描述？ 本博客在此 将上述现象称为： 空间退行性变 (Space degeneration)。 Space degeneration is defined as that any astronaut will suffers from decalcification, amyotrophy, decline in cardiac capability, operating accuracy and working memory and so on while s/he is going into space and taking a journey long enough with spacecraft. 需要补充的是，这是一种可逆性退行性变，即空间乘员从太空返回地面后，可以在一定时间后，获得恢复。 用“空间退行性变，Space degeneration”来描述上述载人航天时，空间乘员所发现的异常生命现象，不知国内外航天同行有什么看法？
If you need to write "8 o N-15 o N," please don't leave extra space everywhere, as in "8 o N - 15 o N." Noted? Another example is "5 o C." This space before " o C" should be removed, though you need a space before most units, such as in "5 cm/s."
Abstract This paper addresses the local displacement at ground stations of the world-wide Satellite Laser Ranging ( SLR ) network induced by atmospheric pressure variations. Since currently available modelling options do not satisfy the requirements for the target application (real-time availability, complete coverage of SLR network), a new representation is developed. In a first step, the 3-dimensional displacements are computed from a 6-hourly grid of 1°×1° global pressure data obtained from the ECMWF, for the period 1997–2002. After having been converted into pressure anomalies, this pressure grid is propagated into horizontal and vertical station displacements using Green’s functions and integrating contributions covering the entire globe; oceans are assumed to follow the inverted barometer (IB) approximation. In the next step, a linear regression model is developed for each station that approximates the time-series of the predicted vertical displacements as well as possible; this regression model relates the vertical displacement of a particular station to the local (and instantaneous) pressure anomaly. It is shown that such a simple model may represent the actual vertical displacements with an accuracy of better than 1mm; horizontal displacements are shown to be negligible. Finally, the regression model is tested on actual SLR data on the satellites LAGEOS-1 and LAGEOS-2, covering the period January 2002 until April 2003 (inclusive). Also, two model elements are shown to be potential risk factors: the global pressure field representation (for the convolution method) and the local reference pressure (for the regression method). The inclusion of the atmospheric pressure displacement model gives improvements on most of the elements of the computations, although the effects are smaller than expected since the nominal effect is absorbed by solved-for satellite parameters. Atmospheric pressure loading displacement of SLR stations D. Bock a , b , c , R. Noomen a , , and H.-G. Scherneck d aDepartment of Earth Observation and Space Systems, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands bRWTH Aachen, Aachen, Germany cUniversity of Stuttgart, Stuttgart, Germany dChalmers University of Technology, Onsala, Sweden Received 22 April 2004; revised 15 November 2004; accepted 19 November 2004. Available online 16 February 2005.
NASA的大气层照片显示大气的层次 蒋迅 老师《从航天器看地球大气层》 http://www.sciencenet.cn/m/user_content.aspx?id=354650 里第一张图片的大图，以及最后一张图。 下载 它们。 可是，从照片还可以清晰地看到大气层的不同层次是怎么看出来的？ 相关：Take a deep breath and then read this http://astrobob.areavoices.com/2010/06/16/take-a-deep-breath-and-then-read-this/ 以下图片无商业用途。 (1) Sunset from the ISS http://www.internet-d.com/?p=9581 Explanation: What are these strange color bands being seen from the International Space Station? The Sun setting through Earths atmosphere. Pictured above, a sunset captured last month by the ISSs Expedition 23 crew shows in vivid detail many layers of the Earths thin atmosphere. Part of the Earth experiencing night crosses the bottom of the image. Above that, appearing in deep orange and yellow, is the Earths troposphere, which contains 80 percent of the atmosphere by mass and almost all of the clouds in the sky. Above the troposphere, seen as a light blue band with white clouds, is the stratosphere, part of the Earths atmosphere where airplanes fly and some hardy bacteria float. Above the stratosphere, visible as a darker blue bands, are higher and thinner atmospheric levels that gradually fade away into the cold dark vacuum of outer space. Sunset is not an uncommon sight for occupants of the International Space Station, because it can be seen as many as 16 times a day. (2) Infographic: Earth's Atmosphere Top to Bottom (infographic by Telescopes for Beginners) http://www.ouramazingplanet.com/earth-atmosphere-layers-atmospheric-pressure-infographic-0326/
《 2001 太空奥德赛》中的生命进化 1968 年 A. C. 克拉克（ A. C. Clarke ）的 小说《 2001 太空奥德赛（ 2001: A Space Odyssey ）》里有关于生命进化的形态的描述。现摘录如下： 感谢 Clarke 和翻译者。以下文字和图片无商业用途。 五、银河系主宰 管它叫 “ 星门 ” 吧。 三百万年以来，它一直在围着土星转，等待着也可能永远不会到来的这一命运攸关的时刻。为了制造它。曾经劈碎一个卫星，至今那卫星的碎块还在轨道上运转。 现在，长久的等侯即将结束。在另一颗行星上，有智慧的生物已经成长起来，正在越出他们的行星摇篮。古老的实验就要达到高潮。 在他们探索的过程中，他们发现各种形式的生命，并且在数以千计的世界上观察到进化的过程。他们看到，在宇宙的黑暗时代，最初的智慧星火一瞬即逝是多么寻常的事。 在他们的调查飞船经过千年的旅程进人太阳系时，巨大的恐龙早已灭绝。飞船扫过冰冻的外圈行星，在正趋向死亡的火星的沙漠上空稍事停留之后，很快就属意于地球。 探索者们发现，在他们眼前展现出一个生命繁茂的世界。他们花了许多年进行研究、搜集和分类。他们把一切都学习到手以后，就开始改造工作。他们对陆地上和海洋中的许多种类都进行了实验。但是究竟哪些实验将会成功，至少要在一百万年之后才见分晓。 他们是耐心的，但他们还不是永生的。在宇宙间有那么多事要做，一千亿个星球都在向他们召唤。所以他们又返回深渊，知道他们再也不会重到这一带地方来了。 再来也没有必要。他们留下来奴仆将继续他们未竟的事业。 在地球上，一次次冰河期到来又复过去，而天上毫无变化的月球仍然保存着他们的秘密。在整个银河系里，文明的消长要比极冰的消失还慢得多。陌生的、美好的、可怕的帝国兴起又衰亡，经验代代相传。他们并没忘怀地球，但重返也没多大意义。 地球只不过是百万个沉默的世界之一，而在百万个里边真会说话的也不多。 他们在这种躯壳中漫游于星际之间。他们不再建造宇宙飞船。他们本身已是宇宙飞船。 但是 “ 机器实体 ” 的世纪很快又已告终。在他们不断的实验中，他们懂得怎样 把知识储存在空间本身的结构里，把思想永久凝聚成光格。他们可以变成辐射性的生物，最终摆脱掉物质的控制。 因此，他们不久又把自己转变成纯粹的能量；他们抛弃在成千个世界上的空壳，先是在失去头脑指挥的情况下抽搐地跳着死亡的舞蹈，随即又锈烂解体。 现在，他们已经成为银河系的主宰， 时间再也奈何不了他们。 他们可以随心所欲地漫游星际，象一层薄雾在空间浮沉。但他们虽已具有神仙般法力，他们并没完全忘记自己的起源，在早已消失的海洋底下的温暖粘土中。 而且，他们还在观察他们祖先很久前开始的那些实验。 37 - Experiment Call it the Star Crate. For three million years, it had circled Saturn, waiting for a moment of destiny that might never come. In its making, a moon had been shattered, and the debris of its creation orbited still. Now the long wait was ending. On yet another world, intelligence had been born and was escaping from its planetary cradle. An ancient experiment was about to reach its climax. Those who had begun that experiment, so long ago, had not been men - or even remotely human. But they were flesh and blood, and when they looked out across the deeps of space, they bad felt awe, and wonder, and loneliness. As soon as they possessed the power, they set forth for the stars. In their explorations, they encountered life in many forms, and watched the workings of evolution on a thousand worlds. They saw how often the first faint sparks of intelligence flickered and died in the cosmic night. And because, in all the galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped. And sometimes, dispassionately, they had to weed. The great dinosaurs had long since perished when the survey ship entered the Solar System after a voyage that had already lasted a thousand years. It swept past the frozen outer planets, paused briefly above the deserts of dying Mars, and presently looked down on Earth. Spread out beneath them, the explorers saw a world swarming with life. For years they studied, collected, catalogued. When they had learned all that they could, they began to modify. They tinkered with the destiny of many species, on land and in the ocean. But which of their experiments would succeed they could not know for at least a million years. They were patient, but they were not yet immortal. There was so much to do in this universe of a hundred billion suns, and other worlds were calling. So they set out once more into the abyss, knowing that they would never come this way again. Nor was there any need. The servants they had left behind would do the rest. On Earth, the glaciers came and went, while above them the changeless Moon still carried its secret. With a yet slower rhythm than the polar ice, the tides of civilization ebbed and flowed across the galaxy. Strange and beautiful and terrible empires rose and fell, and passed on their knowledge to their successors. Earth was not forgotten, but another visit would serve little purpose. It was one of a million silent worlds, few of which would ever speak. And now, out among the stars, evolution was driving toward new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and of plastic. In these, they roamed among the stars. They no longer built spaceships. They were spaceships. But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light. They could become creatures of radiation, free at last from the tyranny of matter. Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds, the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into rusty Now they were lords of the galaxy, and beyond the reach of time. They could rove at will among the stars, and sink like a subtle mist through the very interstices of space. But despite their godlike powers, they had not wholly forgotten their origin, in the warm slime of a vanished sea. And they still watched over the experiments their ancestors had started, so long ago. 请发表您的看法！
Japan always impresses me, a short-term visitor. We know that Japan is small, compared to US or China. Space is clearly an issue. Many Japanese use public transportation routinely. When my girlfriend came to the Narita Airport to pick me up many years ago, I immediately noticed how empty the expressway was and learned why: It is NOT FREEway, as most US expressways are called. Ever since then, I insist on taking a shuttle bus to their home, which is rather convenient. During a recent visit, I snapped this photo for our AOAO: how to use a security chain at an entrance (below). The chain is controlled by a remote controller that each car owner carries in the car. Note also how the 5-car garage system is designed. Showing in the photo is the two levels above the ground; there is another level underground. The middle ground allows only one car to park, and the other side (left or right depending on how the other four cars are used) is to let other four cars out (one at a time). The parking system at this complex is actually more complicated: The cost of parking is determined by the size of a car (width, height, length, etc.) So, do you want to drive a hummer in Japan? It will COST you more just to park!
空间电荷效应space charge effect; 1、所谓的空间电荷效应是指由于电子的分布导致空间存在一个电势的分布.在激光脉冲内这些出射的电子通过逆轫致辐射在激光场中得到能量一方面与气体作用形成气体等离子体 2、 形成了空间电荷层,其电势低于灯丝的电势,称为空间电荷效应.此空间电场会把带负电荷的电子拉回去,抑制电子发射,致使能达到阳极P的电子很小 夫兰克 赫兹实验仪 温度计（ 250 ℃ ） 本世纪初，人类对原子光谱的研究逐步深入，人们发现卢瑟福于 1911 年提出的原子核结构模型与经典电磁理论存在深刻的矛盾。按照经典理论，原子应当是一个不稳定的系统，原子光谱应为连续光谱。但事实上，原子是稳定的，原子光谱是具有一定规律性的分离谱线。为了解决这一矛盾，丹麦物理学家玻尔（ N.Bohr ）根据光谱学研究的成就和普朗克、爱因斯坦的量子论思想，在卢瑟福核式模型基础上，把量子概念应用于原子系统，提出了半经典的氢原子理论，指出原子中存在能级。该模型的预言在氢光谱的观察中取得了显著成功。根据玻尔理论，原子光谱中的每条谱线表示原子从一个能级跃迁到另一个较低能级时产生的辐射。为此， 1922 年玻尔获诺贝尔物理奖。 为了证明原子中电子的运动存在一系列稳定状态 能级， 1914 年，德国物理学家夫兰克 (J.Franck) 和赫兹 (G.Hertz) 巧妙地改进了勒纳用来测量电离电位的实验装置。他们同样采用慢电子（几到几十电子伏）与单原子气体碰撞后电子状态的变化（勒纳观察的是离子）。他们用此装置测定了汞原子的第一激发电位，后又改进电路测出了汞原子的较高激发电位及至电离电位，得到了与原子光谱测量一致的结果，从实验上证实了原子内部能量的分立、不连续性，验证了玻尔理论，为量子理论的创立奠定了实验基础。这两位物理学家于 1925 年获诺贝尔物理奖。 实验原理： 根据玻尔理论的基本假设，原子只能处于一系列稳定状态（简称定态）中，每一稳定状态对应一定的能量值 E n (n=1,2, ) ，这些能量值是彼此分立的，不连续的。原子从一个稳定态过渡到另一个稳定态时，就吸收或放出一定频率的电磁辐射。辐射频率 取决于两定态能量之差 。 原子能量状态的改变可以通过具有一定动能的电子与原子相碰撞进行能量交换来实现。夫兰克 赫兹实验就是通过直接测量出电子碰撞时传递的能量值来证实原子能级存在的。夫兰克赫兹实验的原理图如图 31-1 所示。电子和原子的碰撞是在夫兰克 赫兹实验管中进行的，夫兰克 赫兹管是在抽成真空的电子管中充以某种气体，电子由电阴极发出，阴极 K 与栅极 G 之间的电压 U GK 是使电子加速的；在板极 A 与栅极 G 之间加的是反向电压，它使电子减速，用于探测电子通过 KG 后的状态。这样，电子在 KG 空间被加速时将会与被测气体原子发生碰撞。按玻尔理论，被测气体原子只能接收与其各能级之间能量差相等的能量，而不能接受其他量值的能量。如果电子的动能低于原子第一激发能量，它与气体原子的碰撞将是弹性碰撞，电子几乎不损失能量，因而可能穿过反向电压 U AG 达到板极 A ，被电流计 pA 检出；如果电子加速后具有的动能足够大，足以使气体原子产生激发的话，电子将与气体原子产生非弹性碰撞，把其一部分动能传给原子，使原子从基态跃迁到第一激发态，电子剩下的能量将不足以克服 GA 之间的反向电压，结果将引起板极电流 I A 急剧下降。随着电子继续加速和减速， I A 将随 U GK 周期性的变化， I A -U GK 曲线两峰值之间的电位差就是被测气体原子的第一激发电位。实验观察到的 I A -U GK 曲线如图 31-2 所示。它反映了在 KG 空间中气体原子与电子间进行能量交换的情况。 被测气体可以是惰性气体（如氖、氩气），也可以是汞蒸气。由于常温下汞为液体，因而需要用恒温加热炉，使管中有一定的汞饱和蒸气，其中的原子密度可通过调节加热炉的恒温温度来选择，温度越高管中汞原子密度越大，电子与原子碰撞的机会越多。本实验就是要通过实验测定汞原子的第一激发电位（公认值为 4.9 伏），进而证实原子能级的存在。 原子处于激发态是不稳定的。实验中被慢电子轰击到第一激发态的原子要跳回基态，应有 eU 0 （ U 0 是汞的第一激发电位）电子伏特的能量释放，产生波长为 的光波。 实验中可观察到夫兰克 赫兹管中有淡蓝色的光发出，光谱分析证实了这一波长光波的存在。 假如电子在被加速过程中获得的动能 eU GK 足以补偿原子束缚其电子的势能 eU Z 时，当这样的电子与原子碰撞时，就能从原子中分离出一个电子，使原子变成离子。由于板极电位为负，电子在碰撞后到不了板极，而正的离子才能到达板极形成板极电流 I A 而被电流计检出。通过测量这个电流的变化即可测出该原子的第一电离电位。汞的电离电位是 U Z =10.39V 。
标签: space
