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

Jeff Davis jrd1415 at gmail.com
Thu Jun 11 21:44:31 UTC 2009

```David,

I spent some time on my nightly walk last eve thinking about your
suggested use of lighter than air gasses.  It has both very
substantial positives and negatives, but the more I think about it the
more I like it.  Then there are those negatives.

The structure will involve truly immense quantities of gas.  Air is
free, whereas generating hydrogen in the quantities needed would be
costly.  Exactly how costly needs a calculation.  That said, the
project would be a large one in any event, and perhaps its long term
use would justify the added cost of using hydrogen.  It might even
make the difference between doable and not.

On Thu, Jun 11, 2009 at 6:06 AM, deimtee<deimtee at optusnet.com.au> wrote:
> Jeff Davis wrote:  <snip> ... Air is light.

> 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.

> If you hang a linear accelerator underneath

Yes, underneath or up the side. I blew past Damien's concern re
igniting a rocket on top of a "balloon" for just that reason.  I see
the "tower" as a launch ramp, with the orbital velocity attained at
"manageable" acceleration rates -- re power requirements and g forces
-- in the run up to the tower/ramp.

http://lists.extropy.org/pipermail/extropy-chat/2009-March/048088.html

<snip the tube straightness issue>

> 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).

Quite an impressive amount of lift.  I get virtually the same answer:
525kg and that's per tube.  So double it -- two tubes, right? --  call
it 1050kg per meter.  The tubes themselves are gonna weigh something
of course. And for both tubes, that's 2500 m*2 of tube material per
meter.

Best, Jeff Davis

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

```