一、单元导入

观看下面视频，回答以下问题。

1. Have you seen this movie? 

2. What kind of movie is it?

3. What hi-tech scenes does the video include? 

4. How do you feel about these new technology?

视频来源：【流浪地球2\杜比视界·全景声\4K\60帧】太空电梯超燃混剪！_哔哩哔哩_bilibili

二、太空电梯海报展示：设计时要考虑以下提示。

1. What are the components of space elevators?

2. What could it be used for?

3. What technical challenges could it face?

三、本次课课后的学习任务单如下：

1. 复习本单元PPT内容，背诵PPT中出现的词汇和短语。

2. 自主查阅关于space elevator的视频和资料，了解更多天空电梯的运行原理和相关知识。

本讲PPT课件

四、观看下面的space elevator视频，回答以下几个问题：

1.  How does the space elevator work?

2.  Is it worth to build the space elevator?

3.  What will the space elevator look like in real life?

4.  Can we actually build one? What are the challenges and risks

视频来源：【In a Nutshell】41.Space Elevator – Science Fiction or the Future of Mankind_哔哩哔哩_bilibili

视频英文字幕：

What is space elevators?

It's hard to get to space as much as we allwish. There were an easy and affordable way to see our planet floating in thedark. Right now, the only way is to become an astronaut or a billionaire. Butthere is a concept that might make it possible while serving as the startingpoint for the exploration of the universe, the space elevator. How exactly does it work?To understand how a space elevator will get us into space? We must firstunderstand what an orbit is. Being in orbit basically means falling towardssomething, but moving fast enough to miss. If you throw a ball on earth, itmakes an arc through the air and then hits the ground. In space, gravity makesyou move much the same way. But if you move sideways fast enough, the curvatureof the earth makes the ground fall away beneath you as fast as gravity pullsyou towards it.

So to enter earth's orbit, rockets have togo up and sideways（向侧面） fast. By contrast, a space elevator taps into（利用）energy from the earth's rotation to get the cargo going fast. Imaginea child spinning a toy on a rope with an ant on the child's hand. As the antclimbs out along the rope, it starts to move faster and faster as it ascends. Compared to rockets withcargo launched on an elevator, you only need to provide the energy to go up.Fast sideways movement comes free with the earth's rotation, but a spaceelevator would, without a doubt, be the single, largest and most expensivestructure ever built by humans.

So is it worth it? It all comes down to costs. Rockets burn ahuge amount of rocket fuel just to get a small amount of cargo into space. Atcurrent prices, it costs about $20,000 to put one kilogram of payload intospace. That's $1.3 million for the average human, $40 million for your car,billions for an international space station. This immense cost is one of themajor limitations of human spaceflight, even with advancing technology. Thiscost isn't likely to be comparable with the price of an airline ticket. Anytimesoon. A space elevator would solve this problem. After construction, a spaceelevator is projected to reduce the cost 100 fold to $200 per kilogram. If aninexpensive space elevator costs $20 billion, then we'll recoup（收回） our losses after launching only 1,000,000 tons, close to the weightof two international space stations.

So what would a space elevator look like in real life?A space elevator has four major components, the tether, anchor, counterweight,and climber. The elevator part of the space elevator is the tether and theclimber. It extends from the surface of the earth to space. The climber is likea conventional elevator carriage, a chamber that works its way up and down thetether. At the base would be an anchor, pinning the tether to the earth alongwith the pork for climbers. At the Top is the counterweight which holds up thetether. The tether is held tight like a rope and supported from above by thetension from the counterweight, located higher than 36,000 kilometers above theearth's surface.

At the counterweight could be a spacestation, a launching point for all missions from the spaceport elevator.

But can we actually build one? It's hard to saythe biggest Challenge is the tether. It needs to be light, affordable, and morestable than any material we can produce. Right now. There are promisingmaterials like grapheme and diamond nano threads, but even they may not bestrong enough. And aside from being incredibly strong, the tether would alsohave to withstand atmospheric corrosion, radiation, and micrometeorite anddebris impacts. Additionally, it takes several days to climb the elevator.

How do we power the climber? It requires a lotof energy to go up. Do we need a nuclear reactor on our elevator carriage? Ordo we beam it power from the ground with a super powered laser? And where do weget the raw materials for a 30, 6,000 kilometer long tether? Do we make it onearth and launch it into space? Or do we make it in space and lower it down tothe earth? Could asteroid mining with the answer? Put simply, there are stillsome major technological hurdles to overcome.

A space elevator is not without risk. Shouldthe tether break? It would collapse in spectacular style. If it breaks near theanchor, the force exerted by the counterweight will cause the entire elevatorto rise up ascending into space. Should it break near the counterweight? Thetether will fall wrapping around the world and whipping the end off. Theresulting debris in orbit could pose serious problems to future space flights.If we build a space elevator on earth, we have to do it right the first time.

For these reasons, some experts haveproposed first building a space elevator on the moon. The moon's gravity ismuch weaker than the earth. So a flimsia, but existent material like kevlarcould serve as a tether.

Even with all these challenges, the payoffof having a working space elevator would be immense. It might be the first stepto truly becoming a space faring civilization. Maybe we will never build aspace elevator, but in trying to do so, we might learn an awful lot. When itcomes to the exploration of the universe, there can't be too many dreams of aglorious future.