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So you're proposing blowing vacuum into foam to make vacuum bubbles? |
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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. |
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No [poc] he's proposing blowing bubbles in space then
extracting the gas used to blow them. |
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The idea appears
to lack a purpose though. |
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Does it have one or is it just 'art'? |
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Would the finished article be crushed by ambient pressure
when brought out of vacuum? |
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The idea does not specify bringing it out of vacuum |
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The reason for constructing it in
space is because such a material does not exist & it will get
crushed upon entering atmosphere. |
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Which is plausibly the reason those vacuum ships imagined
hundreds of years ago don't exist yet. |
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1. Orbiting advertising blimps, for new telescopes, as the
only people likely to see them are people looking at the sky
with telescopes. |
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2. Orbital shades to reduce global warming. |
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The problem is, as always, the difference in density - and hence the buyancy- between the "balloon" and the surrounding fluid. |
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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. |
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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". |
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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. |
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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. |
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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. |
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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. |
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Allas, 'tis fated I fear to remain an orbital art installation of
dubious utility. |
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The aggregate density of the entire object needs to be less than 1.225 kg/m3 (ISA) to be buoyant at MSL. |
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At higher altitudes, where the air is thinner, it needs to be even less. |
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Gas balloons can manage with thin, lightweight membranes because they are always close to equilibrium pressure with their environment. |
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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. |
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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. |
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You need a reduction in density of an order of magnitude, and then some, to get close. |
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Let us know how that works out for you. |
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