The Last Post Game!!!!

[Griffin NoName]

One would have to try it on Venus or Jupiter.

No men on Venus. Try Mars.

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[Sibling Zono (anon1mat0)]

Dunno about Venus, but perhaps it would be interesting running the numbers on Titan.

Last _{a titanium shell would be a far better proposal} Post

[Aphos]

Not sure what the atmospheric density is on Titan.  I would think the gravity would be slightly higher than the Moon's...say 1/5 g.

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[Swatopluk]

Gravity would only play a role as far as structural stability goes.
For the floating only the density of the surrounding medium is important.

For titanium the diameter would go from 40 km to 23. Still not a real option.

Last _{not to forget the price} Post

[Sibling Zono (anon1mat0)]

This under the hypotheses that only a 1 mt thick shell will be able to withstand the pressure.

Last _{much thinner} Post

[Swatopluk]

There was also the condition of withstanding heavy artillery. 1 m would be a bit above classic battleship armour but shells have improved too. Modern tanks have a front armour equivalent to slightly above 1 m of common steel (actual armor thinner due to use of composite material an a few other tricks).

In reality a 20 (or even 40) km hollow sphere would likely collapse under its own weight. It would need extensive inner support structures adding to the total weight.

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[Sibling Zono (anon1mat0)]

It sounds way cheaper to just place some ERA in the shell if dealing with artillery is a must.

Last _{if we go by absurd requirements we can use absurd materials like carbon nanotube filament fibers} Post

[Swatopluk]

The original question was : iron balloon, evacuated.

But even with the lightest material you'd stay in the kilometre range.

To get below 1 km you'd have to use material of density <0.8 g/cm³ and a wall thickness <25 cm, again without support structures.

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[Aphos]

Gravity would only play a role as far as structural stability goes.
For the floating only the density of the surrounding medium is important.

For titanium the diameter would go from 40 km to 23. Still not a real option.

Last _{not to forget the price} Post

Ah.  True, that.  I wasn't thinking.

Last _{my bad} Post

[Swatopluk]

Of course, if two planets of the same size with the same amount of gas in the atmosphere had different mass, the atmosphere of the heavier planet would have a higher density near the ground and extend less far out. So floating itself would be easier but greater heights would be difficult.

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[Sibling Zono (anon1mat0)]

A better question would be: has anyone been successful building a vacuum balloon? What would it take with our lightest and strongest materials?

Last _{carbon fiber/klevlar with resin or a titanium alloy} Post

[Swatopluk]

Titanium would still be too heavy to do it in a managable size.
A light composite material, e.g a polymer-ceramics hybrid would imo be the best option.
The material would have to be either extremly stiff, so the hull could be made very thin, or extremly light (e.g. a foam), so a thicker hull could self-stabilise without adding too much weight.

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Edit: the idea is not new btw
http://en.wikipedia.org/wiki/Vacuum_airship

[Griffin NoName]

Can a vacuum airship clean carpets?

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[Swatopluk]

What if it WAS the carpet?

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[Griffin NoName]

It would be self-cleaning like the walls of a modern oven.

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