1.Listen to part of a lecture in a structural engineering class.

2.Today let’s begin to look at structural engineering in the Space Age

3.Uh

4.new problem

5.new possibilities mean we can think in new ways

6.find radically different approaches

7.So let’s consider

8.uh

9.well

10.what would you say is the biggest obstacle today to putting structures

11.equipment

12.people

13.uh

14.anything really

15.into space

16.Well

17.the cost

18.right

19.Exactly

20.I mean

21.just taking the space shuttle up and back one time is hugely expensive

22.Uh

23.Uh

24.why

25.I guess a lot of it is for fuel

26.right

27.To…to get the rocket going fast enough

28.OK

29.Fast enough to…

30.To escape Earth’s gravity

31.Good

32.So we are burning up an enormous amount of fuel at every launch just to get the rocket up to what’s known as escape velocity

33.Now

34.escape velocity is around 11 kilometers a second

35.pretty fast

1.But do we really have to go this fast

2.Well

3.yeah

4.I mean

5.how else can you

6.um…escape

7.I mean

8.that’s the whole point of escape velocity

9.right

10.Otherwise gravity will pull you back down to the Earth

11.Actually

12.that’s a common misconception

13.[Escape velocity is simply the speed of an object that’s …uh

14.let’s say

15.shot out of a cannon the minimum initial speed so that the object could later escape Earth’s gravity on its own

16.But that’s just if there’s no additional force being applied

17.If you keep on supplying force to the object

18.keep on pushing it upward

19.It could pull away from Earth’s gravity at any speed

20.Even really slow

21.So you’re saying …like

22.if you had a ladder tall enough

23.you could just climb into space

24.Yeah

25.Uh

26.well

27.theoretically

28.I mean

29.I can see some practical problems with the ladder example

30.Uh

31.like you might get just a little bit tired out after the first few thousand kilometers or so

32.uh

33.especially with all the oxygen tanks you’ll have to be hauling up with you

1.No

2.I was thinking more along the lines of an elevator

3.Wait

4.You are serious

5.sure

6.An elevator

7.That’s a new idea to most of us

8.but in fact it’s been around for over a century

9.If we could power such an elevator with solar energy

10.we could simply rise up into space for a fraction of the cost of a trip by rocket or shuttle

11.But wait

12.elevators don’t just rise up

13.It have to hang on some kind of wire or track or something

14.Uh

15.true

16.And for decades that’s exactly what’s prevented the idea from being feasible or even just taken seriously

17.Where do we find the material strong enough yet lightweight enough to act as a cable or track

18.I mean

19.we are talking 36,000 kilometers here

20.And the strain on the cable would be more than most materials could bear

1.But a new material developed recently has a tensile strength higher than diamond

2.yet it’s much more flexible

3.I am talking about carbon nanotubes

4.OK

5.I’ve read something about carbon nanotubes

6.They are strong

7.alright

8.but aren’t they just very short little cylinders in shape

9.Ah

10.yes

11.But these cylinders cling together at a molecular level

12.You pull out one nanotube or row of nanotubes

13.and its neighbor’s come with it

14.and their neighbors

15.and so on

16.So you could actually draw out a 36,000-kilometer strand or ribbon of nanotubes stronger than steel

17.but maybe a thousandth the thickness of a human hair.

1.OK

2.Fine.

3.But what’s going to hold this ribbon up and keep it reach enough to support an elevator car

4.Well

5.we definitely have to anchor it at both ends

6.So what we need is a really tall tower here on the ground right at the equator and a satellite in geostationary orbit around the Earth

7.There’s a reason I mentioned that figure of 36,000 kilometers

8.That’s about how high an object would have to be orbiting straight up from the equator to constantly remain directly above the exact same spot on the rotating planet Earth

9.So once you are in this geostationary orbit right over the tower

10.just lower your carbon nanotube cable down from the satellite

11.tether it to the tower here on Earth

12.And there you have it

1.so you really think this is a possibility

2.Like

3.how soon could it happen

4.Well

5.the science fiction writer Arthur C

6.Clarke talked about building a space elevator back in the 1970sAnd when someone asked him when he thought this idea might become a reality

7.his reply was

8.“Probably about fifty years after everybody quits laughing.”