Airship to orbit - cities in the sky

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

Semantics......you must have done the experiment at school or uni where you
evacuate a tin can and watch it collapse....

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

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......and if the structure cannot support that it will collapse
(well it did when I studied Engineering anyway)

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

It is still greater, ergo your balloon structure must resist those forces,
and a floppy one will not without some rigididity in the structure somewhere

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

How does this stop the pressure differential acting across the balloon
surface?

> A.P.: "..how would one do this without a rigid structure?"
>
> 2. The structure need not be absolutely rigid.

No, but somewhere there will need to be a rigid frame or something...c'mon,
thats semantics, you know what I'm saying. I would be interested is seeing
your proposed non-rigid structure to hold a vacuum against an outside
pressure....somewhere you are going to have to brace or support something.

Alan