Can we now build the space elevator?

From: Robert Clark (rgregoryclark_at_yahoo.com)
Date: 08/29/04 

Date: 29 Aug 2004 08:01:49 -0700

============================================================
From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Re: beanstalks (was Re: Metallic hydrogen ...)
Newsgroups: sci.physics, sci.astro, sci.space.policy, sci.materials,
sci.energy
Date: 2004-06-09 02:06:53 PST
 

henry@spsystems.net (Henry Spencer) wrote in message news:<HyzyFx.DIH@spsystems.net>...
> ...
> Given that the nanotubes themselves are far thinner than even a one-micron
> ribbon, any material technology that ties them together into bulky
> materials should work just as well for such ribbons, with some adjustment
> in the details of manufacturing. Even such a ribbon *is* a bulky
> material, when the fibers involved are nanotubes.
> ...

 Tie?
 Hmmm. Do you think it might work to tie the ends together of the 20
centimeter long nanotubes already produced?
 Looking up some links on knots, the knotted ropes always have less
strength than the single, unbroken ropes. I confirmed this by testing
on sewing thread.
 Still it might be interesting to find out how strong they are
compared to single nanotubes.

    Bob Clark
============================================================

 Testing with thread confirmed that a break always occurred where two
strands were tied together. However, to estimate the strength of a
single strand of thread, I wrapped two ends around my fingers and
found that the break occurred in the middle of the thread, not where I
was holding the thread. My guess was that the softness of my fingers
prevented the thread from breaking at the attachment point (where I
was holding it.) I confirmed this by holding one end by a pair of
pliers and the other end with my fingers. The break occurred where the
pliers held the thread. However, when I put a soft cloth between the
thread and the pliers, the break occurred in the middle of the thread,
as when I was holding both ends with my fingers.
 I imagine this must actually be a common way of testing tensile
strength. That is, you don't want to attach the strand or rope to
something that will make the rope break at the attachment point. This
would give an invalid measure of the rope strength. You want it to
break somewhere in the middle.
 I therefore suggest connecting together the already produced 20
centimeter long nanotubes with a soft material or by whatever means
used to insure nanotubes don't break at the attachment point during
tensile strength testing. This will allow the full strength of the
nanotubes to be maintained even when they are connected together.
 What will need to be investigated is what soft material will also be
light enough so as not to cancel out the weight savings of using the
nanotubes. Note that this soft material might be heavier than the
nanotube material but because it only has to be used at the
connections it can be quite small so quite conceivable may only add
minimally to total weight.
 It still needs to be confirmed that the macroscopic sized nanotubes
really are as strong as the nanotubes tested on the microscale.
 This report showed that 20 centimeter interwoven strands were
significantly weaker than the tested individual microscale nanotubes:

Direct Synthesis of Long Single-Walled Carbon Nanotube Strands.
Science, Vol 296, Issue 5569, 884-886 , 3 May 2002
http://www.sciencemag.org/cgi/content/full/296/5569/884

 However, the theory is that this is because there were many single
nanotubes connected together by weaker van der Waals forces rather
than the stronger carbon-carbon molecular bonds that prevail in
individual nanotubes. This is explained here:

Pulling nanotubes makes thread
http://www.trnmag.com/Stories/2002/103002/Pulling_nanotubes_makes_thread_103002.html

 What still needs to be tested is the strength of the *individual*
nanotubes that make up these 20 centimeter long strands.

 This article describes a group that proposes that competively offered
prizes could make possible the technologies required for the space
elevator by 2010:

Space elevator contest proposed.
‘Elevator:2010' aimed
at encouraging technology development.
http://www.msnbc.msn.com/id/5792719/

    Bob Clark

Relevant Pages

  • Re: Can we now build the space elevator?
    ... We are also developing ultra long carbon nanotubes. ... >> materials should work just as well for such ribbons, ... > strength than the single, ... > strands were tied together. ...
    (sci.materials)
  • Re: Can we now build the space elevator?
    ... The space elevator may be the biggest environmental disaster ever waiting to ... >> materials should work just as well for such ribbons, ... when the fibers involved are nanotubes. ... > strands were tied together. ...
    (sci.physics)
  • Re: Can we now build the space elevator?
    ... We are also developing ultra long carbon nanotubes. ... >> materials should work just as well for such ribbons, ... > strength than the single, ... > strands were tied together. ...
    (sci.physics)
  • Re: Can we now build the space elevator?
    ... The space elevator may be the biggest environmental disaster ever waiting to ... >> materials should work just as well for such ribbons, ... when the fibers involved are nanotubes. ... > strands were tied together. ...
    (sci.astro)
  • Re: Can we now build the space elevator?
    ... We are also developing ultra long carbon nanotubes. ... >> materials should work just as well for such ribbons, ... > strength than the single, ... > strands were tied together. ...
    (sci.astro)