
Vacuum airship - ejr
https://en.wikipedia.org/wiki/Vacuum_airship
======
idlewords
The linked articles from the 1887 New York Times are wonderful:

"The means by which passengers will be landed en route is also in doubt. Some
suggest that they will simply be dropped overboard and their luggage thrown
after them, while others maintain that a coil of greased rope for the purposes
of descent will be carried on each and every machine."

Truly the Hyperloop of its day.

[http://query.nytimes.com/mem/archive-
free/pdf?res=9904E7D815...](http://query.nytimes.com/mem/archive-
free/pdf?res=9904E7D81538E533A25757C1A9649C94669FD7CF)

~~~
waps
This is a problem that every zeppelin faces too. They can't easily gain or
lose height, because that would mean losing the gas they need to stay
airborne.

A vacuum ship that actually has a vacuum pump aboard would have the great
advantage that it can easily change it's buoyancy using, say, electrical
power. It could use this to change height, or compensate for being loaded with
materials.

Vacuum ships would actually be a solution to the zeppelin problem.

~~~
idlewords
A zeppelin could use compressor tanks to control its buoyancy in an exactly
analagous way. Lots of details on how the problem was handled in practice
here:

[http://en.wikipedia.org/wiki/Buoyancy_compensator_(aviation)](http://en.wikipedia.org/wiki/Buoyancy_compensator_\(aviation\))

------
beloch
At atmospheric pressure, a given volume of hydrogen weighs approximately 7%
(there is some variation with temperature) of an equivalent volume of air. All
that is needed to contain hydrogen at atmospheric pressure is a membrane it
can't pass through. The inwards force exerted on the membrane by the
atmosphere is perfectly balanced by the outwards force exerted by the hydrogen
gas. The only structural material required is for the purpose of harnessing
the lifting power of the enclosed gas, providing an aerodynamic shape, etc..

Conversely, a vessel containing a vacuum must be built to withstand the
101,325 N/m^2 net inward force exerted upon it by the atmosphere that is not
balanced by the outward pressure of the contents of the vessel. Consider, for
a moment, what you would need to build a 1 m^2 coffee table out of if 20
elephants were to be able to stand on top of it at once.

For the sake of argument, let's say that we had a magical material that would
let us build a replica of the Hindenburg that is of equal weight to the
original, only with vacuum vessels replacing the hydrogen bags. The Hindenberg
contained 200,000 m^3 of hydrogen lift gas, weighing 1,798 kg and displacing
enough atmosphere to provide a total lift of 25,850 kg, 10,000 kg of which
were considered it's cargo capacity beyond the passengers it carried. This new
version of the Hindenberg, despite being built with materials and techniques
that are probably well beyond our current level of technology, would carry the
same number of passengers and just 18% more cargo.

For those of you who think that vacuum vessels are a lot safer than hydrogen,
I'd like to remind you that the atmosphere surrounding 200,000 m^3 of vacuum
provides a rather huge amount of potential energy waiting to be released. When
vacuum vessels of a large size fail the resulting implosion can be both
spectacular and devastating.

[https://www.youtube.com/watch?v=Zz95_VvTxZM](https://www.youtube.com/watch?v=Zz95_VvTxZM)

------
phkahler
I have wondered if such a thing could be designed for use in the upper
atmosphere and dropped in from space. That would avoid the need to keep out
the full atmosphere. But then so would pumping out the air as it gained
altitude...

~~~
refurb
But if dropped into the upper atmosphere where there is little air pressure,
it would sink until it got to an altitude where it's weight equaled the mass
of the atmosphere it was displacing.

~~~
jjoonathan
That would be the point.

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tsotha
This is an idea that seems interesting at first glance, but it's really not.
What's important for lift isn't the absolute weight of the gas; it's the ratio
of the weight of the lifting gas to the surrounding air. What that means is
while hydrogen gives you about 1kg/m3 lift a perfect vacuum bottle only gives
you about 1.3kg/m3. It probably wouldn't make sense even if we had the
necessary exotic materials.

------
olefoo
The major weakness of a vacuum airship is that a breach of the pressure hull
will compromise the vacuum and thus the buoyancy. So any truly useful solution
will require a number of independent vacuum cells.

The strongest shape made of compressive members is a tetrahedron, if surfaced
with an impermeable and inelastic membrane an evacuated aerostat could end up
looking like
[http://www.theatlantic.com/video/archive/2012/01/a-gorgeous-...](http://www.theatlantic.com/video/archive/2012/01/a-gorgeous-
floating-crystal-inspired-by-alexander-graham-bells-kites/251224/)

------
digikata
I wonder if a modern materials would let us build lift cells in this vein -
maybe thin-skinned vessels filled with aerogel for structural support.

~~~
jcampbell1
> "This cannot even be achieved using diamond"

The whole concept totally absurd. Helium is ~15% the density of air, so even
if you created a material 100x stronger than diamond, it would only outperform
helium by a tiny amount.

~~~
titanomachy
The helium in a balloon/dirigible is under pressure, so its density would be
somewhat greater than 15% that of air. But point taken.

~~~
coryrc
No. It's always the same pressure as air. That's the point. It'll always be
~15%.

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aaron695
Misses the point hydrogen is safer, easier, could be done today with existing
tech for commercial travel (Already used a lot for scientific balloons) and
pretty much has the same lifting power.

(Also Helium is obviously currently is used in airships commercially with no
real problems on top of a theoretical vacuum ship other than perhaps cost of
balloon contents, which I'd guess is not the limiting factor anyway)

~~~
spiritplumber
A problem with Hydrogen is that it is very reactive -- that doesn't
necessarily mean fire, but it does mean that any surface it comes into contact
with will be affected. For example, you can't fill a latex balloon with
hydrogen and expect it to last very long.

~~~
refurb
Hydrogen, at normal pressures, isn't that reactive at all if you ignore it's
combination with oxygen.

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dj_gitmo
This rail-bound tank was probably not designed with weight savings as a prime
considerations.
[https://www.youtube.com/watch?v=Zz95_VvTxZM](https://www.youtube.com/watch?v=Zz95_VvTxZM)

Still, this is a fascinating idea and I would love to see someone make a
serious attempt at it.

~~~
panzi
Yeah, but as the Wikipedia article states: not even diamond is strong enough.
So don't hold your breath.

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valarauca1
Its a cool idea but as the post suggests air pressure on the vacuum spheres is
a major problem. The crush force on the sphere will scale 40x the lift factor.
So 1 gram of lift, 40 grams of crush.

Once you reach scales of 10,000 kilograms you'll be dealing with keeping
400,000 kilograms of weight out of your vacuum.

~~~
idlewords
The advantage over hydrogen at atmospheric pressure is really minor, too.

~~~
porpoisemonkey
That's true for buoyancy but vacuum definitely has a major advantage in area
of flammability.

~~~
k__
What happens if a vacuum sphere that can lift 10t implodes?

~~~
dredmorbius
You lose 10t of lift.

If a hydrogen envelope of 10t ruptures, you lose 10t of lift _and_ have a
major fire hazard.

~~~
idlewords
You lose 10t of lift in a horrifyingly destructive implosion:
[https://www.youtube.com/watch?v=Zz95_VvTxZM](https://www.youtube.com/watch?v=Zz95_VvTxZM)

~~~
dredmorbius
And here's what hydrogen does.

Note the comparison is of a pure H₂ vs. 2 χ H₂ + O₂ mix.

[https://www.youtube.com/watch?v=qOTgeeTB_kA](https://www.youtube.com/watch?v=qOTgeeTB_kA)

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m-i-l
Reminds me of an idea I had for lighter than air packing material. It was
going to be something like over-sized bubble wrap filled with helium, or
balloons you'd insert into the spaces and inflate with a helium canister.
Seems a great idea at first, but then you do the maths, and think about the
materials. Unfortunately the weight savings are likely to be so minimal
they're unlikely to save on postage costs, and even if they did reduce postage
they're likely to be outweighed by the cost of materials. Plus you later find
out that lots of other people have had the same idea and posted on the
internet about it.

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lpmay
This reminds me of Buckminster Fuller's cloud 9 concept. His idea was that
since volume scales so much more strongly than surface area for a sphere, if
you make a larger and larger sphere you will enclose cubed more air for only
squared more structure. Build a large enough sphere and heat the enclosed air
a couple degrees above ambient and the entire structure would be buoyant, like
a soap bubble with human breath in it.

[http://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_sphere...](http://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_sphere%29)

~~~
ianbicking
"Geodesic spheres (structures of triangular components arranged to make a
sphere) become stronger as they become bigger, due to how they distribute
stress over their surfaces."

I happened upon some Bucky Fuller stuff recently, and wondered just how large
geodesic spheres have been made... and it's not particularly large. Which
makes me wonder: is this really the whole story? What is the flaw in geodesic
spheres that keeps them from being the basis of huge enclosed structures?

~~~
Synaesthesia
The difficulties of construction for one, and such large structures are
vulnerable to buckling I would imagine.

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ChuckMcM
These are fun (also in Diamond Age I believe) and I like how they are both
impossible to create and there is a patent application on them :-)

It is interesting to run the structure density vs the vacuum numbers. I always
wondered if we would be able to make vacuum filled bucky balls out of carbon
at some point.

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rotten
Does the vacuum have to be perfect? Maybe you can reduce the pressure on the
surfaces, and therefore simplify the engineering, by leaving some air in
there. I think it is an interesting idea that varying the internal pressure
would change your lift. You only ever need "just enough" lift anyhow.

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hacknat
14% advantage over helium makes it seem like it's not worthwhile. Am I missing
something?

~~~
kansface
Helium is a finite resource- escaped Helium eventually leaves our planet
forever; nuclear fusion will probably never produce sufficient helium for
current industrial use.

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jccooper
"His patent application was eventually denied on the basis that it was 'wholly
theoretical, everything being based upon calculation and nothing upon trial or
demonstration.'"

He'd get that patent today. Little as it might avail him.

