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

[Jeff Davis]

On Wed, Jun 10, 2009 at 10:37 AM, Damien Broderick<thespike at satx.rr.com> wrote:
> At 03:05 AM 6/11/2009 +1000, David wrote:
>
>> Spike, regarding your idea of pressurizing to 20 times atmospheric in a
>> vertical tube
>
> Isn't Spike's notion a stack or cone of smaller and smaller annuli, each
> independently pressurized?

Excellent, excellent discussion.  My life is complete.  I can go into
cryonic suspension with a smile on my face. (I want my dewar to have a
little window behind which that smile can be seen, and my hand raised
in a wave.  Perhaps a little curtain with a drawstring for mutual
privacy and to avoid overexposure.  But I digress.)

I think Spike meant a simple single layer cone, however... This is the
design process: ideas go out, are critiqued, and revised.  Sometimes
you reach a dead end, scrap the mark 12 and move on to the mark 13.

Here Damien provides an example of communication "noise" leading to a
new design variant.  Inflated tubular sub-elements.

Inflated tubular sub-elements which give rise to enhanced local
rigidity in the structure, is good. It has a place.  The design
process will have to run its course for us to see where that place is.

Spike remarked that the hoop stress at the base of his cone was huge.
Yes, partly because he has such a high -- 20 atm -- inflation
pressure, but mostly because the larger the diameter of a pressure
vessel the larger the hoop stress .  This makes a cone WITH AN OPEN
INTERIOR problematic.  But the solution is quite simple.
Compartmentalize the interior. Fill the conical space with stacked,
inflated spheres.  I think you will then find the pressures necessary
to hold up the stack to be very very much less that the 20 atm
overpressure of spike's Mark 1.  Because the bigger the diameter of
the pressure vessel (the big inflated sphere) the greater the bearing
capacity for a given internal pressure.  Fat tires, low pressure;
narrow tires, high pressure.

Now a note on beauty.  While the skin of any such proposed inflated
structure is the strength member, and is in tension, the air inside,
clearly essential, is in compression.  This **is** a compression
structure.  But the "blocks" that support the load are made of air.
Blocks of air.  Air is light.  The blocks are "light as air".  It is
that lightness of the major building component which makes possible
the magnificent parsimony of bulk and mass in the overall structure.
(The final design of which, has admittedly yet to be determined.)

Breathtakingly beautiful.

Best, Jeff Davis

 "Everything's hard till you know how to do it."
                         Ray Charles