Airship to orbit - cities in the sky

Re Digest 1074

Message: 3 From: "Alan Patrick"

A.P.: "Any structure that has a vacuum inside and pressure outside
needs to ensure that it can resist the forces of implosion..."
Patrick,

1. "Implosion" is a bit strong, "Collapse" might be better..

-But as Andy said ""Current balloons tend to have virtually the
same gas pressure inside as outside the envelope."

-At sufficiently high altitudes air pressure is not much greater
than the so-called vacuum of space.

Besides: when I suggested construction take place in space I
had other considerations in mind, most importantly,
-ground level weather.

There is still the problem of high altitude winds and
temperature variance. Perhaps the answer would be to seek an
"optimal" altitude with some atmosphere let in rather than
just the greatest altitude achievable.

-This would allow buoyancy control thru heat management.

In the original B.Fuller design buoyancy was dependant upon air
temperature. The claim was that heat from every day activities,
..even body heat would be sufficient to maintain buoyancy.

A.P.: "..how would one do this without a rigid structure?"

2. The structure need not be absolutely rigid.

Rem: "The oak breaks, the reed bends."

[as Thor Heyerdahl discovered when designing transatlantic reed
boats :-]

Also geodesic structure is surprisingly strong. Just this week
I saw [on TV] a couple of kids who constructed a geodesic dome
in just a few minutes, about 2.5 +/- feet high out of not very
neatly rolled newspaper. When done, the dome was capable of
supporting the weight of one of the kids.

Also, I would assume that the internal structures, living
quarters, flight deck, etc. would be supported more or less
centrally by some sort of "tensegrity" arrangement of cables
with multiple points of attachment, which might actually
strengthen the "balloon's" overall structural integrity .

See:
http://www.google.com/search?sourceid=mozclient&ie
=utf-8&oe=utf-8&q=tensegrity

or, http://tinyurl.com/67qux [which is the same thing reduced]

Re message: 5 From: "Andrew Goddard"

A.G: "I misinterpreted your suggestion ... as the url'd proposal was
to do things the other way around: fly up materials from Earth
and launch them to orbit from floating platforms."

1. There was nothing in the URL which proposed "flying" things up..
nor was there anything in it related to "space" or "launching".
"Cloud 9" was simply a floating city at no great altitude.

2. But most importantly:

To "fly" materials up would defeat the whole purpose !!!!

3. My 'take' was that materials could be lifted up in much the same
manner as they would be by the Space Elevator.

4. -This would no doubt require suitable tethering, probably by
CNT cables.

A.G:"a geodesic-dome-meeting-zeppelin-bracing - that structure would
need to be extraordinarily resilient to inward pressure forces,
whether from very thin air in the upper atmosphere,..."

5. I have no reason to believe that a properly designed geodesic
structure would not be sufficiently resilient. This would pose
a problem however with regard to a cable supported infrastucture.
There would have to be some equivalent to spring loaded cables
or some other kind of "shock absorber".

-As regards "zeppelin-bracing", see "tensegrity" above.

6. Also, as I suggested above, there would be no objection, and in
fact there would be a benefit from allowing air in to balance
pressure until optimum altitude was reached.

A.G."..or while the structure was being deorbited from 7km/s to float
in upper atmosphere winds."

7. Structural materials would have to be brought to a geostationary
orbit before construction could begin.

A.G.:"As I understand it, even at 400km the density of the atmosphere
changes markedly in relation to the solar cycle."

8. The questions are:

a. How rapidly do these changes take place, and can they be dealt
with by heat management protocols?

-If by "solar cycle" you mean normal daily and seasonal changes,
then the answer is probably "Yes".

-and,

b. What would be the nature of unpredictable events at a given
altitude?

[i.e., unusual weather events..., sunspots...,other ?]

RKH