[ExI] Inflatable tower could climb to the edge of space

[spike]

...
> > >>
> > >> MY IDEA.  MY IDEA.  MY ORIGINAL IDEA.  ORIGINATED BY MOI.
> ME, MY, MINE...I just want recognition as the guy who thought 
> of it first... Best, Jeff Davis
> 
> 
> ...Having a tower reach to 30km 
> would allow us to launch with very little, if any, payload 
> fairing.  I have some interesting findings to post a little 
> later this evening if I get a chance... spike


OK I had a chance to do a few BOTECs today and found some interesting stuff.
I assumed a tower that must reach to an altitude of about 30km.  That way,
the rocket nozzles can be optimized for vacuum, since the air density is
about 1.4% the altitude at the deck, so it is close enough to a vacuum
there.

I had in mind a cone shape, since nature has given us trillions of examples
of towers in that shape, trees.  I assumed the material would be steel,
since it is a good structure material in terms of specific strength,
abundance and cost.  Steel is what a mechanical engineer would call an
isotropic material, since its strength in tension, compression and shear are
similar and not dependent on direction, unlike wood, which is strongly non-
isotropic.

If we assume an inflatable tower built of an isotropic material, we find
that inflating the tower does little good unless one wraps the tower with a
high tension material horizontally.  Imagine a conic tower made of steel,
then imagine pumping in nitrogen until the weight of the tower is supported
by air pressure.  Now the material at the base of the tower is not in
compression in the vertical direction, but is in enormous tension in the
horizontal direction.  With this configuration, much of the available
strength of the steel is wasted.  Sooo...

Oddly enough, the way to do this sort of structure would be to make the
steel thinner than in the above example, then wrap it horizontally with
strands of aramid fiber, held in place by a coat of epoxy.  This would make
the tower lighter and use far less total material than an all-steel tower.
More later.

spike