# What materials and what shapes should be used for struts inside a vacuum airship's envelope?

What materials and what shapes should be used for struts inside a vacuum airship's envelope?

The vacuum airship is a theoretical dirigible design were you replace the hydrogen/ other lifting gas with a vacuum. The density of air at standard temperature and pressure is 1.28 g/l, so 1 liter of displaced air has sufficient buoyant force to lift 1.28 g. The problem with this is that you must have a strong and rigid envelope so that it does not collapse under the pressure of the atmosphere. I think one way to resolve this would be to have struts made out of light and stiff material (e.g graphene) and to have an incredibly rigid envelope made out of similar materials.

So, what shape should the struts be (both individual shape and how they are placed), and what should they be made out of? If you have an alternative to the struts then you may answer with that.

https://en.wikipedia.org/wiki/Vacuum_airship

• "This can lift up to 1.85 times its weight in one bar of atmosphere": What does this even mean? And the lift of an airship filled with hydrogen is only marginally lower than the lift of the same volume of vacuum -- 1.1 kg / cubic meter instead of 1.2 kg / cubic meter. The extraordinary complicated engineering does not offer more than a measly 9% more lift per unit of volume. Oct 24, 2019 at 23:56
• Sorry that this was unclear. I meant "The density of air at standard temperature and pressure is 1.28 g/l, so 1 liter of displaced air has sufficient buoyant force to lift 1.28 g," this is compared to "the mass of helium (at 1 atmospheres of pressure) is found to be 0.178 g. If helium is used instead of vacuum, the lifting power of every liter is reduced by 0.178 g, so the effective lift is reduced by 14%. A 1-liter volume of hydrogen has a mass of 0.090 g." en.wikipedia.org/wiki/Vacuum_airship Oct 25, 2019 at 2:47

A single envelope is inherently dangerous. One single pop and everyone is sky diving - minus the parachute.

Even the great airships of yester year worked around this by not having a single compartment filled with hydrogen/helium, but by having many smaller bladders organised for easy maintenance and attached to the airframe. The outer skin was for aero dynamics.

To that end my advice would be to construct many smaller vacuum vesicles. These will of course present a less efficient buoyancy as there will be a higher material to space ratio. On the plus side though you can construct these in the must efficient shape - a sphere - and forego internal reinforcement structures as the surface thickness is sufficient to offset any implosive tendencies.

This general concept can handle some fairly extreme pressure differentials, just take a look at the research and engineering on deep sea submersibles. The Marianas trench, the deepest part of the ocean with the highest most crushing pressure, was traversed by a submersible with humans inside. While not strictly a vacuum on the inside (insert pun of your choice) the difference in pressure between the inside and outside of that vessel was extreme.

As for materials, I am unsure what would be suitable. Glass definitely has the capability to maintain high quality vacuums at sea level. However I'm pretty sure that it is far too heavy to be usable for an airship. Otherwise we would have some very interesting science toys.

Metals could indeed fill the gap, but they too have issues. Corrosion is one, but i believe they are still limited here in that the thickness required places it as too heavy.

I suspect you would be most interested in space age fabrics such as those used in the Bigalow space hotels. Perhaps these with a minimal (perhaps spherical) bar frame. The fabric could obviously be refined more, as certain properties needed for space are useless in atmosphere. But there is a start.

Either way there are better ways than internal struts to distribute compression forces.

A geodesic sphere would be one of the best structural shapes. Depending on the strength of the materials used and the size of the airship required, internal struts could then be run from any node through the centre of the sphere to a corresponding diametrically opposite node. Graphene would be a good choice of material. Made into tubular form for the struts and stretched as a fabric over the outer surface.

Assuming you have access to room-temperature superconductors, you can make a vacuum air bubble by wrapping a lightweight sphere in the superconducting wire and running current through it. The magnetic field built up can provide the structural integrity and prevent the vacuum vessel from collapsing or buckling (if one part of the sphere starts to buckle inwards, the magnetic field pushes it outwards, stronger).

Your airship would essentially be a large container for these large spherical bubbles.