p116-p117 ＜ LANDMARK English Communication Ⅰ｜啓林館デジタル教科書

The space elevator needs an <span class='nw'>extremely</span> long cable. /

It must be about [100,000] km long. /

That is about

eight times / as long as the Earth’s diameter! /

Such a

long cable will be broken / by the pull of the Earth’s

gravity / and the centrifugal force. /

Therefore, / the

cable has to be more than 100 times / as strong as

<span class='nw'>steel</span>. /

Until the 1990s, / no one knew / what kind of

<span class='nw'>material</span> would be strong enough / for this cable. /

This

had been the biggest problem / for the <span class='nw'>development</span> / of

the space elevator. /

In 1991, / [Dr.] Sumio Iijima, / a Japanese scientist, /

discovered a <span class='nw'>potential</span> material / for the cable / of the

space elevator. /

It is called a “<span class='nw'>carbon</span> <span class='nw'>nanotube</span>.” /

this material did not <span class='nw'>exist</span>, / the space elevator would

remain / only in science fiction. /

Carbon nanotubes are

made of carbon / and are the lightest and strongest

material / on Earth. /

They are about [50,000] times /

as <span class='nw'>thin</span> as a human hair / and 100 to 150 times / as

strong as steel. /

However, / there is one problem / with

carbon nanotubes. /

They are still very expensive /

because they can only be produced / in <span class='nw'>tiny</span> amounts. /

As a result, / many <span class='nw'>researchers</span> are working hard / to

make their mass <span class='nw'>production</span> possible. /

Questions

Q5	It needs an extremely long (and strong) cable.

Questions

Q6	(He discovered) A potential material for the cable of the space elevator. [(He discovered) “Carbon nanotubes.”]

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