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closed cell foam extruded in vacuum

vacuum formed shell enclosing vacuum sphere
 
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Extrude closed cell insulation foam into a vacuum to form a thin low density foam walled shell. Remove all or partial air from shell to create vacuum balloon.
supdoc, Aug 03 2020

Foam Hulled Spacecraft Foam Hulled Spacecraft
[zen_tom, Aug 03 2020]

Vacuum Airship https://en.wikipedi...wiki/Vacuum_airship
An idea that's been floating around since 1670 [kdf, Aug 03 2020]

Displacement Buoyancy & The Art Of Not Crashing Your Satellite Displacement_20Buoy..._20Your_20Satellite
[Skewed, Aug 03 2020]

Project Echo https://en.wikipedi...g/wiki/Project_Echo
Shiny! [kdf, Aug 04 2020]

[link]






       So you're proposing blowing vacuum into foam to make vacuum bubbles?
pocmloc, Aug 03 2020
  

       I can't be sure if this was your intention, but this sounds like a far more succinct version of an idea I got quite into a while back.
zen_tom, Aug 03 2020
  

       No [poc] he's proposing blowing bubbles in space then extracting the gas used to blow them.   

       The idea appears to lack a purpose though.   

       Does it have one or is it just 'art'?
Skewed, Aug 03 2020
  

       D'art?   

       Would the finished article be crushed by ambient pressure when brought out of vacuum?
whatrock, Aug 03 2020
  

       The idea does not specify bringing it out of vacuum
pocmloc, Aug 03 2020
  

       I'm reading this as a suggestion to create a vacuum balloon, the last words in the original write up. If the "low density foam" was light and strong enough to NOT get crushed upon returning to atmosphere, the structure would have terrific useful buoyancy. Effectively a vacuum airship as imagined hundreds of years ago. (link)
kdf, Aug 03 2020
  

       Naturally [kdf].   

       Howsoever.   

       The reason for constructing it in space is because such a material does not exist & it will get crushed upon entering atmosphere.   

       Which is plausibly the reason those vacuum ships imagined hundreds of years ago don't exist yet.
Skewed, Aug 03 2020
  

       Skewed - Naturally, obviously, and fersher. I was trying to answer your question if it had a purpose - vacuum airship was my guess at supdoc's intent, regardless of whether it would work or not. *IF* a feasible material existed, it might be easier to constructing it a vacuum as supdoc suggests, rather than building it at sea-level, pumping air out, and then sealing it closed. I'm not championing the idea, just pondering.
kdf, Aug 03 2020
  

       If it existed yes.   

       Possible uses.   

       1. Orbiting advertising blimps, for new telescopes, as the only people likely to see them are people looking at the sky with telescopes.   

       2. Orbital shades to reduce global warming.
Skewed, Aug 03 2020
  

       The problem is, as always, the difference in density - and hence the buyancy- between the "balloon" and the surrounding fluid.   

       Consider a sphere containing vacuum, created in space, using Unobtainium VacuGel- like aerogel, but with vacuum- so the structure is extremely light yet infinitely strong.   

       But at the edge of the atmosphere the air's very thin, and the disposable lift of the sphere is the difference between its mass and an equivalent volume of rarefied air, which is "not a lot".   

       The same sphere submerged in water would experience a large buoyancy force, but importantly not significantly greater than that experienced by an identical sphere pressurized with normal air to match that of the surrounding water.
8th of 7, Aug 03 2020
  

       The Borg still use Unobtainium VacuGel? That went out of style after Button Humpage the III had his scientists develop stabilized mono-layer neutronium. He had them all killed afterwards so he could keep the secret and exploit it himself, but word gets around.
kdf, Aug 03 2020
  

       Stepwise: 1. Extrude closed cell foam into a low pressure or vacuum chamber...the propellant would expand the cells greatly compared to extruding foam at STP...the foam would be strong but low density. 2. This foam extrusion would somehow be used to form a hollow shell...maybe by joining two clam shells, etc. 3. The hollow shell would be hermetically sealed and then the shell room air evacuated to a near vacuum. 4. With appropriate dimensions...Voila...a low density, hard shell, LTA balloon.
supdoc, Aug 04 2020
  

       The only problem of course is that even ignoring any difficulties of reentry (such as friction leading to combustion) with all extant materials it can never enter the atmosphere without sinking & ultimately getting squashed like a styrofoam cup at the bottom of the Mariana Trench.   

       So perhaps can't be called a // LTA balloon // as it doesn't fulfil the basic requirements of such, namely that it should float in air.   

       Allas, 'tis fated I fear to remain an orbital art installation of dubious utility.
Skewed, Aug 04 2020
  

       The aggregate density of the entire object needs to be less than 1.225 kg/m3 (ISA) to be buoyant at MSL.   

       At higher altitudes, where the air is thinner, it needs to be even less.   

       Gas balloons can manage with thin, lightweight membranes because they are always close to equilibrium pressure with their environment.   

       It might just be possible to make a very small buoyant sphere this way, but as the volume increases the square/cube law ratios (surface area to volume) impose huge compressive forces. That's why bathyspheres tend to be somewhat cramped inside.   

       If you could make a closed-cell foam with vacuum inside the cells instead of gas, and very small cell geometry, that might help. Typical low-density closed-cell polyurethane foam has a density of about 48 kg/m3; that's a factor of about 40 heavier than standard air.   

       You need a reduction in density of an order of magnitude, and then some, to get close.   

       Let us know how that works out for you.
8th of 7, Aug 04 2020
  

       Speaking of inflated, orbital art installations - see Project Echo link.
kdf, Aug 04 2020
  
      
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