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colossal 35,790 km above the earth - is a measure of the challenge facing engineers. How could
such a height be reached?
The answer is by using an incredibly strong and lightweight cable, strong enough to
support its own weight and a heavy load. The design of such a cable is still largely theoretical.
This would be attached to a base station on earth at one end and a satellite in geostationary orbit
(fixed above a point on the equator) at the other. Lift vehicles would then ascend and descend
the cable, powered by electromagnetic force and controlled remotely.

7a James, an engineer, is giving a talk on space elevators. Complete his notes using the
correct form of the verbs (1-7) in Exercise 5a.

 Challenge of (1) connecting satellite to earth by cable is significant.
 To (2) its own weight, and be securely (3) at each end,
cable would need phenomenal strength-to-weight ratio.
 How could vehicles be (4) into space, up cable?
 Self-contained energy source problematic, due to weight (heavy fuel or batteries required
to (5) vehicle).
 Two possible ways round problem:
1 Transmit electricity wirelessly. Hut technique only at research stage.
2 Solar power. But would only allow vehicle to (6) slowly. Not
necessarily a problem, as car could be controlled remotely, allowing it to (7)
payloads unmanned.

7 b Read the part of James’ talk and check your answers in Exercise 7a.
James: The engineering challenge of connecting a satellite to earth using a cable is, obviously,
significant. In order to support its own weight, and be securely attached at each end. the cable
would require a phenomenal strength-to-weight ratio. Carbon nanotube materials might, one
day, be up to the job. And I’ll talk about those in detail later on. How could vehicles be raised
into space, up the cable? Well, using a self-contained energy source would be problematic, due
to the weight of fuel or batteries required to power the vehicle. There are two possible ways
round this problem: transmitting electricity wirelessly, or using solar power. The first technique
is only in the early stages of research. The second would allow the vehicle to ascend only very
slowly, though this wouldn't necessarily be a problem, as the car could be controlled remotely,
allowing it to transport payloads as an unmanned vehicle.

8 a James goes on to discuss offshore base stations. Read the conversation
and answer the following questions.

1 How would an offshore base station be supported?
2 What would the function of its anchors be?
3 How would payloads reach the base station?
4 What problem would a mobile base station help to prevent?
5 What would the procedure be if there was an alert?

James: The offshore base station would be supported by a floating structure, which could be
attached to the seabed by anchors. Payloads could be carried from the shore to the station by
ship before being lifted into orbit. The main advantage of a floating mobile station, rather than a
fixed base on land, would be to help reduce the risk of a collision between the cable and one of
the many lumps of space debris, such as redundant satellites, that litter orbital space. Based on
careful monitoring of debris movements, in the case of an alert the station's anchors could be

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