Airship to orbit - cities in the sky

Message: 2

From: "Alan Patrick"

AP: "Well obviously, as they stay inflated - but they aren't
supporting vacuums......If pressure outside is greater than
a vacuum, the forces will be inward."...

RKH: I believe its the gradient of inward forces which account for
buoyancy, but read on..

AP: "I would be interested in seeing your proposed non-rigid
structure hold a vacuum against an outside pressure...
somewhere you are going to have to brace or support something."

RKH: I suspect that a properly constructed geodesic sphere could
survive and be strengthened [made more rigid] by slightly
negative internal pressure so long as there are no seriously
unbalanced external forces. However, if you will refer to my
previous msg. you will see that the point is moot as I point out
the advantages of admitting 'some' air.
Of course, the less you admit the higher the balloon will float,
but the object would be to find the optimal,not necessarily the
greatest, altitude.

Also,If the balloon contains sufficient air, and if buoyancy is
made a function of heat, then we may assume that the pressure
inside is greater than outside.

In any case, if construction takes place in space you will
necessarily begin with a vacuum,[altho moderate pre-pressuriza-
tion is an option] and then hold at the greatest altitude con-
sistent with stability/manageability. CNT tethers will help.

[Note that at sufficient altitude the outside pressure might be
considered a [relative] 'vacuum' at sea level. :-]

>> When I suggested construction take place in space I had other
>> considerations in mind, most importantly, -ground level
>> weather.

As you may imagine there would be serious problems trying to
construct a sphere a mile or more in diameter on the ground.
And while those problems are likely soluble, weather
permitting, -I believe construction in space would be compara-
tively straightforward.
Its a question of considerable engineering and physical
bother vs the expense of sending up astronauts and/or robots
to perform a task which is essentially the same as working
with a giant erector set.

RKH

P.S. -Sorry about my "Tensegrity" link. #:-/

Here are some URLs about "Cloud Nine", although googling

-Buckminster Fuller domes- [which are common]

would give a clearer understanding of geodesic construction.

http://www.cjfearnley.com/fuller-faq-5.html#ss5.2

see also May 29 at:

http://www.duntemann.com/may2004.htm

.