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Dynamically-stabilised vacuum balloon

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As mentioned in the first-linked idea, materials like glass are strong enough to make a vacuum balloon out of, in theory. The crushing strength of glass is high enough.

Unfortunately, this only applies to a perfect sphere with no uneven loads and no flaws. If such a sphere is even slightly imperfect, or if you stress it unevenly by attaching something to it, then the sphere will deform slightly. This will lead to positive feedback failure, with the balloon "oilcanning" - the glass will fail in bending rather than compression.

In the second-linked idea, I talked about tall, thin columns. They are unstable in a similar way - once they bend even slightly, there's positive feedback and the column will collapse in bending long before the crushing strength of the material is reached. I suggested that such a column could be dynamically stabilised using (say) piezos to counter any deflection before it runs away.

So, how about a dynamically-stabilised vacuum balloon? It's made of a mundane material like glass (which can support the necessary load in compression), but the faces are coated with piezos with dynamic, local control. If an unbalanced load deflects one part of the wall by a tiny amount, the piezos act to oppose that deflection before it leads to oilcanning collapse.

In this way, you should be able to construct a workable vacuum balloon, although it would only survive as long as the dynamic control was working. It would be nice to have some sort of self-actuating control; for instance, if you made the surface out of suitably modified silicon (coated with a piezo on one side), it could incorporate local solar cells, strain gauges and amplifiers that maintained stability.

MaxwellBuchanan, Jul 06 2019

Vacuum balloons come up here self-supporting_20railgun
[MaxwellBuchanan, Jul 06 2019]

Piezo-stabilised struts Piezo-stabilized_20strut
[MaxwellBuchanan, Jul 06 2019]

Not really "bending"... https://en.wikipedia.org/wiki/Buckling
The word you want is "buckling" [neutrinos_shadow, Jul 07 2019]

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       How much does the control system weigh?
pocmloc, Jul 06 2019
  

       That's the critical factor. However, we're talking mainly about a piezo layer on one surface of the balloon.
MaxwellBuchanan, Jul 06 2019
  

       More "buckling" than "bending" failure (but it does bend once it's buckled...).
Is a vacuum balloon really that desirable? Sure it's plenty buoyant in theory, but once you add the complexity (& therefore weight) of all the extra whatsits, you might lose any advantage.
Oh, idea I just had: vacuum is pulling IN, so you need an OUTward force to compensate. Make it mostly disc-shaped and spin it.
neutrinos_shadow, Jul 07 2019
  

       Any collapsing force just has to be vectored away. A very thin crash helmet for the soft vacuum balloon head inside. As [neutrinos_shaddow] indicated it could be dynamic and made partially made from the air around the balloon.
wjt, Jul 08 2019
  

       // Is a vacuum balloon really that desirable? // I think the main advantage is that vacuum can be produced on-site, using solar power if necessary. A lifting gas is generally harder to produce. Also there is the theoretical possibility of more buoyancy per unit volume, but considering the difficulty in making the structure to light enough to float at all, that would have to be considered a "stretch goal".
scad mientist, Jul 08 2019
  

       I was wondering about using hot helium instead of vacuum. The aim, of course, is to get useful buoyancy at extremely high altitudes. Ambient hydrogen will get you so far (about 100-130,000ft), but if were heated to (say) 1000°C, its density would be only one third as much. Since the balloon is operating at extreme altitude, the hydrogen would already be very, very rarefied; and thermal losses would be lower by being in near-vacuum.
MaxwellBuchanan, Jul 08 2019
  

       You discuss spheres and cylinders as potential shapes for this balloon. Would it not be possible to combine these and create a balloon with all the complexity and disadvantages of both shapes by making a toroidal glass balloon?
hippo, Jul 08 2019
  

       Going for really far fetched, the inversion of a magnetic bottle. Couldn't a magnetic field be generated between a bunch of atoms and slowly made wider, brushing atoms aside, forming a volume of no gas. Obviously the field would have to increase in strength relative to scale of volume needed. Maybe only half a solid shell is needed.
wjt, Jul 08 2019
  

       Why not rapidly rotate a glass cylinder to offset the inwards pressure on the equator?
AusCan531, Jul 09 2019
  

       Motors with magnets are quite heavy.
wjt, Jul 09 2019
  

       // Couldn't a magnetic field be generated between a bunch of atoms and slowly made wider, brushing atoms aside// I think you'll only be able to brush aside ions; neutral atoms or molecules will just stay where they are.   

       Having said that, plasma windows can support pressure differences of several atmospheres. The only problems are that (a) they use vast amounts of power and (b) the force on the window has to go somewhere - presumably into the apparatus surrounding the window, so you haven't really gained anything.
MaxwellBuchanan, Jul 09 2019
  

       //(b) the force on the window has to go somewhere// into the reaction that's trying to be achieved, hopefully. In this extreme bit of fancy, flight.   

       If glass was embedded with a correct angular magnetic component , wouldn't that would mean the ion species are deflected, lowering the pressure ever so slightly?
wjt, Jul 10 2019
  
      
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