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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.
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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Annotation:
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How much does the control system weigh? |
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That's the critical factor. However, we're talking mainly
about a piezo layer on one surface of the balloon. |
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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. |
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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. |
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// 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". |
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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. |
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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? |
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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. |
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Why not rapidly rotate a glass cylinder to offset the inwards
pressure on the equator? |
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Motors with magnets are quite heavy. |
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// 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. |
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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. |
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//(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. |
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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? |
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Spheres really are a good shape for resisting
pressure efficiently. Reinforce where you have
point loads from attachments etc. - that’s really
the best you can do, structurally. |
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//best you can do, structurally// |
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There are active structural system components, a structure is maintained with help by the input of energy. If extrapolated, might be a underlying principle in the future. |
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//a underlying principle// Sp. "a nunderlying principle" |
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[Max] , Don't you think there will ever be a material that becomes a lot stronger when continually applied the correct pattern of electricity? as a hypothetical example. |
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It's possible. Whether it would be a material or a structure is
unclear, although complex materials like wood are really
structures. |
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Isn't that the whole concept of metamaterials? |
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Problem is, how does the alloy systo-matic search for attributes undiscovered yet? Someone has to trip over the anomaly first, or imagine new mathematics, to have the inkling to look in that obscured direction. |
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Did you annotate the wrong idea? |
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All Grist to the mill when searching for vacuum balloon materials. |
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