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#### Climb into Space

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What is the main purpose of the lecture?
• A. To help students understand what is required to launch a satellite

• B. To describe new materials now being used to explore space

• C. To describe a potential technology for space exploration

• D. To show how ideas from science fiction often develop into actual technologies

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NARRATOR:Listen to part of a lecture in a structural engineering class.

MALE PROFESSOR:Today, let's begin to look at structural engineering in the Space Age.Uh, new problems... new possibilities, um, mean we can think in new ways... find radically different approaches.So let's consider, uh- well... What would you say is the biggest obstacle today to putting structures, equipment, people, uh-anything, really-into space?

FEMALE STUDENT:Well, the cost, right?

MALE PROFESSOR:Exactly. I mean, just taking the space shuttle up and back one time is hugely expensive. Uh, why?

FEMALE STUDENT:I-I guess a lot of it's for fuel, right? To-to get the rocket going fast enough...

MALE PROFESSOR:[encouragingly] OK... fast enough to...?

FEMALE STUDENT:To, uh, escape Earth's gravity.

MALE PROFESSOR:Good! So we're burning up an enormous amount of fuel at every launch, just to get the rocket up to what's known as "escape velocity."

Now escape velocity is around 11 kilometers a second-pretty fast. But-do we really have to go this fast?

FEMALE STUDENT:[confused] Well... yeah! I mean, how else can you... um, escape?I mean, that's the whole point of escape velocity, right?Otherwise, gravity will pull you back down to the Earth...

MALE PROFESSOR:Actually, that's a common misconception.Escape velocity is simply the speed of an object that's, uh, let's say, uh, shot out of a cannon... the minimum initial speed so that the object could later escape Earth's gravity on its own.But that's just if there's no additional force being applied.If you keep on supplying force to the object, keep on pushing it upward, it could pull away from Earth's gravity at any speed.

MALE STUDENT:Even really slow?[light dawning] So you're saying, like, if you had a ladder tall enough, you could just climb into space?

MALE PROFESSOR:Yeah-uh, well, theoretically. I mean, I can see some practical problems with the ladder example.Uh, like, you might get just a little bit tired out after the first few thousand kilometers or so- uh, especially with all the oxygen tanks you'd have to be hauling up with you!

No, I was thinking more along the lines of an elevator...

MALE STUDENT:[continues chuckling for a second, then does double take] Wait, you're serious?

MALE PROFESSOR:Ah, sure. An elevator- uh, that's a new idea to most of us, but in fact it's been around for over a century.If we could power such an elevator with solar energy, we could simply rise up into space- for a fraction of the cost of a trip by rocket or shuttle!

MALE STUDENT:But wait-elevators don't just "rise up"- they have to hang on some kind of wire, or track, or something...

MALE PROFESSOR:Uh, true-and for decades that's exactly what's prevented the idea from being feasible, or even just taken seriously: Um, where do we find a material strong enough, yet light weight enough, to act as a cable or track.I mean, we're talking 36,000 kilometers here- and the strain on the cable would be more than most materials could bear.But a new material developed recently has a tensile strength higher than diamond, yet it's much more flexible.I'm talking about carbon nanotubes.

MALE STUDENT:OK, I've read something about carbon nanotubes-they're strong, alright, but aren't they just very short little cylinders in shape?

MALE PROFESSOR:Ah, yes, but- these cylinders cling together at a molecular level.You pull out one nanotube, or row of nanotubes, and its neighbors come with it. And their neighbors, and so on.So you could actually draw out a 36,000-kilometer strand or ribbon of nanotubes, stronger than steel, but maybe a thousandth the thickness of a human hair.

FEMALE STUDENT:OK, fine, but what's gonna hold this ribbon up? And keep it rigid enough to support an elevator car?

MALE PROFESSOR:Well, we'd definitely have to anchor it at both ends.So what we'd need is a really tall tower here on the ground, right at the equator, and a satellite in geostationary orbit around the Earth.

There's a reason I mentioned that figure of 36,000 kilometers- that's about how high an object would have to be orbiting, uh, straight up from the equator, to constantly remain directly above the exact same spot on the rotating planet Earth.So once you're in this geostationary orbit, right over the tower, just lower your carbon nanotube cable down from the satellite, tether it to the tower here on Earth, and there you have it!

FEMALE STUDENT:So you really think this is a possibility? Like, how soon could it happen?

MALE PROFESSOR:Well, the science fiction writer Arthur C. Clarke talked about building a space elevator back in the 1970s.And when someone asked him when he thought this idea might become a reality, his reply was, "Probably about 50 years after everybody quits laughing."

• 旁白：听一段结构工程学课程。

教授：今天我们开始讲太空时代的结构工程学。新的问题......新的可能性，代表着我们也能从新的角度思考，找出完全不同的方法。想想......你觉得今天来说，要把结构、设备、人......任何东西吧，送入太空，最大的障碍是什么？

学生：成本吧？

教授：完全正确。我的意思是，仅仅是把太空船送出去再回来一次就已经是极度昂贵的了。为什么呢？

学生：我猜大部分（钱）花在燃料上，对吧？因为火箭的速度要足够快。

教授：好。足够快以......

学生：以挣脱地球引力。

教授：对。我们每次发射都会燃烧掉大量的燃料，来让火箭达到所谓的“逃逸速度”。

逃逸速度大约在每秒11公里，这非常快。但，我们真的需要这么快吗？

学生：要吧。我是指，要不然你怎么能......逃出去呢？这是逃逸速度的全部意义所在，不是吗？否则引力会把你拉回地球。

教授：事实上这是普遍的误解。逃逸速度就是某物体的速度......这么说吧，某物体从大炮中发射出来所具有的最小初速度，这速度能让该物体之后自行挣脱地球引力。但这种情况是没有额外外力的情况。如果你持续给该物体提供动力，不断把它往前推，任何速度下它都能摆脱地球引力。

学生：哪怕它很慢？你说的是......如果你有一个足够高的梯子，你能直接爬进太空？

教授：对。理论上来说。我是指，我能想出梯子这个例子中一些实际应用中的问题。比如，在爬完刚开始的几千公里后，你可能会觉得有点累，特别是你还要带一大堆氧气罐一起爬上去。

我的想法更偏向于电梯那方面。

学生：等等！你是认真的？

教授：当然，电梯。这对我们来说是个新奇的想法，但事实上这种想法已经存在超过一百年了。如果我们能用太阳能给电梯供能，我们就能直接升上太空，成本不过是火箭或太空船之旅的一小部分。

学生：等等，电梯不是自己就会升上去的。电梯要悬挂在缆线或轨道或别的什么上。

教授：对。几十年来，这正是这种设想不可行或不被严肃对待的原因：我们上哪里去找出一种强度足够高但又足够轻的材料来做缆线或轨道呢？我们说的可是三万六千公里啊。缆线上的张力要比大多材料所能承受的还要大。但最新开发出了一种新材料，其抗张强度比钻石还高，而且更柔韧灵活。我说的是碳纳米管。

学生：我看过一些关于碳纳米管的资料。碳纳米管强度是很高，但它们的形状不是很短小的圆柱体吗？

教授：啊，对。但从分子水平上看，这些圆柱体都是紧密结合在一起的。你取出一个纳米管，或一排纳米管，它们的邻居（相邻的纳米管）也会随之取出，还有邻居的邻居等等。所以，你真的能够拉出一条三万六千公里长的纳米管线，或者纳米管带，其强度比钢铁要高，但其厚度可能只是人类头发的千分之一。

学生：好吧。但要用什么来支撑这条纳米管带，让它能伸得足够远来支撑升降机呢？

教授：肯定是两端都要固定住的。所以我们需要赤道地面一个非常高的高塔，和沿地球静止轨道绕地运转的卫星。

这是我提到三万六千公里这个数字的原因。一个物体要想在赤道正上方绕轨运转，且一直保持在自转地球的正上方的同一位置，该物体就要达到这个高度。一旦你在塔正上方的地球静止轨道上，就可以从卫星直接放下碳纳米管缆线并绑在地球地面的高塔上。然后就解决了！

学生：你真的认为这有可能吗？要多久才能实现？

教授：科幻小说作家亚瑟·C·克拉克在20世纪70年代就提过建造太空电梯。当有人问他什么时候这个设想会成真，他回答，“在没人对此付诸一笑后，大概还要五十年吧。”

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解析

题型分析：主旨题

原文定位

Professor: Today let’s begin to look at structural engineering in the Space Age. Uh, new problems…new possibilities mean we can think in new ways, find radically different approaches. So let’s consider…uh, well, what would you say is the biggest obstacle today to putting structures, equipment, people …uh, anything really, into space?

选项分析

章开门见山引出主旨 structural engineering in Space. 然后着重描述New possible 以及different approaches

C选项即为文章核心new approaches to space的同义替换，是对全文主旨最准确的概括

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