
The US military is testing stratospheric balloons that never have to come down - jonbaer
https://www.technologyreview.com/s/612417/darpa-is-testing-stratospheric-balloons-that-ride-the-wind-so-they-never-have-to-come-down/
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bfirsh
The article fails to mention these are called "superpressure" balloons in case
you're interested in reading more about them:
[https://en.m.wikipedia.org/wiki/Superpressure_balloon](https://en.m.wikipedia.org/wiki/Superpressure_balloon)

There are some fantastic amateur projects doing similar things, such as this
11 gram payload (!) that circumnavigated the earth 6 times:
[http://leobodnar.com/balloons/B-64/index.html](http://leobodnar.com/balloons/B-64/index.html)

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rmason
Do you know what materials they use to make these balloons? Weather balloons
can go as high as 100,000 feet and then they'd blow up.

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Tepix
AFAIK they only blow up because they're designed that way.

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ProblemFactory
Bursting is not a goal in itself - it is just a side-effect of using cheap and
simple latex or rubber balloons.

You fill the balloon so it has slightly positive buoyancy. As it rises, it
encounters lower outside air pressure, and expands to match it. Eventually it
will rise to an altitude where the pressure is so low, that the latex is
stretched beyond its limits and bursts. Typically at about 40km and about 100x
expansion in volume.

To prevent bursting, you need a more complex material that will expand many
times at first (to allow the balloon to rise to operating height), but will
then stop expanding without breaking.

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14
Or perhaps some sort of venting system that engages at a certain altitude or
pressure preventing the ballon from over expanding. Like a hot water tank has
a pressure release it the tank gets too hot will vent releasing pressure.

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londons_explore
Venting does not work. For a given altitude, there is no amount of helium
which will make your craft stable unless the volume of your craft is non-
linear with pressure (usually done by having something that stretches to a
limit, and then cannot stretch further)

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smueller1234
From reading the actual article, the headline sounds dramatically overblown.
It largely talks about a system to measure non local wind speeds so the
balloon can adjust altitude to use the wind for navigation (including standing
still). It seems to largely leave out any questions I'd have around confining
helium or whether power equilibrium can be achieved.

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kylehotchkiss
Don't balloons expand in the day and contact at night a bit due the sun
heating the gas inside? Couldn't this stretch/release weaken the material a
little and result in potential gas leaks?

To counteract this, I recall reading about people trying to send balloons
across the Atlantic and needing to use ballast to stabilize the altitude and
handle the gas losses. I wonder how DARPA can go without this requirement, as
Helium really likes to escape whatever it's trapped inside of.

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sehugg
Maybe the balloon could condense water in its environment and electrolyze it
to refill itself with the produced hydrogen. (Though I'm pretty sure you also
need salt.)

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thrower123
If a balloon is relatively small, and designed never to come down, would it be
such a bad idea to use hydrogen as the lifting gas? We're understandably a
little gunshy about using hydrogen after the Hindenburg, but surely we could
come up with some safer designs now.

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FlyMoreRockets
Hydrogen is a great lifting gas, but because the molecule is so small, it
leaks out easily.

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josefresco
I read a lot of books about the US involvement in the middle east,
specifically Iraq, Afghanistan and Pakistan.

These persistent, balloon based "eyes on the sky" are/were a huge difference
maker in the security in Iraq, and were then transferred to Afghanistan to
provide US military base security.

I don't have a link handy (I'll try to find), but I remember as attention was
re-focused on Afghanistan (after Iraq) those in charge were eager to bring
this successful tech to the battlefield as it offered them a 360 degree, real
time tracking ability for immediate base security.

Edit: I found a link, not _my_ source but it gives some background:
[https://www.nytimes.com/2012/05/13/world/asia/in-
afghanistan...](https://www.nytimes.com/2012/05/13/world/asia/in-afghanistan-
spy-balloons-now-part-of-landscape.html)

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cozzyd
To my knowledge, there has been one successful SPB scientific payload that
made it across the Pacific. SPB-EUSO was less successful...

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Tepix
How do these balloons change their altitude? Is there a pump that can move gas
between the balloon and a pressurized container?

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bradleysmith
At least at loon, the balloon has a ballonet that takes on atmosphere as
ballast for descending.

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londons_explore
A balloonet is a small balloon inside the big balloon. By filling it with air,
you are adding mass to the craft without changing the crafts volume.

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sosorry44
Amateur ballooning blog
[http://www.leobodnar.com/balloons/](http://www.leobodnar.com/balloons/)

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Cantonese
Someone should post the ballooning guys blog. He used metal balloons that
stayed afloat for days and went around the world.

