[geeks] Carbon nanotube buckytape

[Charles Shannon Hendrix]

Fri, 19 Aug 2005 @ 21:15 -0400, Phil Stracchino said:

> Dave Fischer wrote:
> > Stronger than steel by weight. So how strong is 30kg of steel
> > stretched out to cover a sq. kilometer?
> 
> I don't know ...  the article doesn't say how *much* stronger by weight.

There are two issues to consider in terms of strength:

    - carbon cables require less material
    - carbon cables reduce total strength needed as a result of #1

In other words, they don't have to hold as much of their own weight
in addition to payload.  Steel cables often weigh more than they are
lifting.

Drifting topic:

Same basic problems for rockets: the rockets greatly outweigh what
they lift because their propulsion is so inefficient.  That's another
fascinating area of research.  What we need is not a rocket, but a
space-propeller, we just don't know what to push against.

One physisist whose talk or paper I read explained it like this:

If you replace "spacecraft" with "submarine", it is relatively easy to
show just how inefficient a rocket is.

Imagine the submarine has a water-rocket instead of a screw

To cross the Atlantic, a submarine would have to store all of the water
that would normally pass through a screw, plus all the water needed to
generate thrust to move the water itself (the reactive mass).

In other words, it would be just as ridiculous as trying to build a
reactive propulsion system to reach Alpha Centauri.  The fluid ratios
are simply horrible.  A rocket is the same: the fluid you pass through
(volume of space occupied by rocket) is tiny compared to the fluid you
must store on board.

That's why all spacecraft we have are forced to cruise powerless for
over 90% of their mission, with bare minimum maneuver abilities.  It's
not just that we can't cover distance, we can't even maneuver well over
short distances.

It's obviously in the realm of science fiction, but the end results of
any kind of space screw are so compelling that its not ignored any more.

The most current research is on quantum vacuum and how it might be used.
You still must provide the energy of course, but you no longer have to
provide the reactive mass of a rocket.  

Anyway, combine that with a space elevator, and things would change very
quickly.



-- 
shannon "AT" widomaker.com -- ["If you tell the truth, you don't have to
remember anything" -- Mark Twain]