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

deimtee deimtee at optusnet.com.au
Thu Jun 11 13:06:30 UTC 2009

Jeff Davis wrote:

>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
Actually, my point was that in the quantities we are discussing, air is 
NOT light.  Air at sea level
masses slightly over 1 kg /m3.   It is not a perfect gas, but near 
enough for BOTECs.  That means that
you can simply multiply the volume in cubic metres by the pressure in 
atmospheres and get a rough mass in kilograms.

I had another idea about the almost-horizontal-lighter-than-air tube.
If you hang a linear accelerator underneath in needs to be kept damn 
near perfectly
straight during launches.  The structure itself may be capable of 
flexing, but near the
 end the projectile is moving so fast that a deviation of only a few 
metres per kilometre
will result in unacceptable sideways stresses.  However if you have two 
tubes, side by side
and hang the acccelerator beneath them on pairs of cables, so that the 
cables form a V
shape, you could put quick-acting winches on each cable under computer 
control to keep
the accelerator dead straight. 
I may have messed it up, but I calculated that a pair of hydrogen filled 
tubes 200 m in
diameter would give a lift of 500kg  per metre of length, at 1.4% 
atmosphere (Spike's
figure for 30km high). 


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