# Can we make rigid floating helium spheres?

Is there any material that we can make rigid floating helium spheres out of without it collapsing?

I have been playing with surface area and volume formulas and with a bit of trial and error have come up with some best fit figures for 1mm thick aluminium and carbon fibre sheets.

For aluminium the diameter would be about 15 meters and for carbon fibre about 10 meters.

Figures used and workings.

Air 1.225 kg/m^3 Helium 0.164 kg/m^3

1mm thick. Aluminium 2.6 kg/m^2 Carbon fibre 1.8 kg/m^2

15 meter sphere Air 2164.74 kg Helium 289.81 kg Aluminium 1837.81 kg

10 meter sphere Air 641.39 kg Helium 85.86 kg Carbon fibre 565.47kg

Ps. Is there an easier way to find an exact ratio rather than trial and error?

I don't know about the collapsing part. But apart from the structural integrity, yes, it is possible to have buoyancy with rigid bodies. Actually, you wouldn't even need the gas.

See here

Actually, I am currently looking for investment to make a proof of concept of this type of airship with a certain types of light weighted materials :)

I found the following condition for buoyancy of a vacuum sphere:

$[1 - (R_{inner}/R_{outer})^3] \rho_{material} < \rho_{air}$

where $R_{inner}$ and $R_{outer}$ are the inner and the outer radius of the sphere, respectivelly.

$R_{outer} - R_{inner} =$ thickness of the sphere wall

• I think the gas would help a lot to stop collapse and the gains from a vacuum I see as negligable. – Jitter Jan 7 '14 at 17:50
• of course it would, but it would also add weight – cinico Jan 7 '14 at 17:54
• Yep but if you double the diameter you start to get tons of extra lifting capacity. – Jitter Jan 7 '14 at 18:03
• yes, in either cases – cinico Jan 7 '14 at 18:04