phil osborn wrote:
> Unfortunately, the "square/cube law" that works against you re heavier than
> air flying things, works for you in much the same proportion re lighter than
> air craft. I've often thought that you ought to be able to build a vacume
> dirigible, using foamed metal or ceramic for the hull. The hull would be
> very thick, but actually thin relative to the total size. If you built in
> orbit and figured out how to get it down into the atmosphere, you could end
> up with a permanent airostat with quite a lot of lift left over.
I did some calcs on this today. Looks to me like the vacuum dirigible
notion doesnt work out. If one uses only idealized assumptions regarding
the strength of materials, and assumes assembling a spherical vacuum
ship on orbit, ignoring how to lower the thing into the atmosphere, etc,
then one sees that the mass of the atmosphere displaced increases as
the cube of the linear dimension, but the mass of the sphere also increases
as the cube, since the surface area increases as the square of the
diameter and the thickness increases proportional to the diameter.
Looks to me that even assuming a hollow diamond sphere, we
still arent in the vacuum dirigible business. Dammit. {8-[ spike
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