Float into space?

[Adent]

Say you construct a hollow, perfect sphere in space using a very rigid and very lightweight material. If you could keep it from crumpling during transit through the atmos all the way to the ground (cargo of a shuttle or something)... if it was lightweight enough would it shoot up when it was released, like a balloon underwater?

[Savage117]

Nope, it would more likely sink under the balloons weight because its filled with a vacuum. The reason a balloon shoots out of the water like that is because its full of air, and air is lighter than water, there is also the pressure of the water against the balloon and some other concepts I don't want to go into right now. A vacuum is the complete lack of gas or liquids, so there is literally nothing inside the balloon, except tiny amounts of space dust or whatever. They have several vacuum chambers at the NASA training center for vacuum testing, and these are basically big metal balloons and they don’t go shooting up into the air or even get light enough to float when the air is pumped out. Hopefully that covers it, but that's a pretty simple way to put it, hope I haven't offended any of the science buffs in this forum for simplifying it so much.

[3_bit]

Well, you could do it if you were to use spider string or carbon nanotubes, but both are highly impractical. However, they are both many times stronger and lighter than steel. *Maybe* you could do it. I would much rather fill it with extremely low-pressure hydrogen, and slowly vent it as you go up, so that the external air pressure (We're already dealing with a VACUUM here!) won't have as much of an impact. Of course, that's all hypothetical physics.

[Faark]

It depends... you would have to make your sphere lighter than the same volume of atmosphere. In that case it would definitively ascend into the sky. But the atmosphere is a lot lighter than water, so there will not be that much acceleration, while the terminal velocity will not be very high (compared to a rocket) and you are constantly fighting gravity. I doubt it will reach a much higher altitude than whatever it evens out at the end, and that won't be very high as well. Anyway, even if you would reach ISS altitude (and that will never happen), you would still need more than 7km/s dv to actually reach orbit[*], so you don't rly save much...

[K^2]

Nope, it would more likely sink under the balloons weight because its filled with a vacuum. The reason a balloon shoots out of the water like that is because its full of air, and air is lighter than water, there is also the pressure of the water against the balloon and some other concepts I don't want to go into right now. A vacuum is the complete lack of gas or liquids, so there is literally nothing inside the balloon, except tiny amounts of space dust or whatever. They have several vacuum chambers at the NASA training center for vacuum testing, and these are basically big metal balloons and they don’t go shooting up into the air or even get light enough to float when the air is pumped out. Hopefully that covers it, but that's a pretty simple way to put it, hope I haven't offended any of the science buffs in this forum for simplifying it so much.

You are absolutely wrong. The buoyancy is simply equal to displaced weight. Vacuum is, in fact, the perfect filler for a balloon. It gives you 100% buoyancy. The reason vacuum chambers don't float is because they are heavy. Really, really heavy. They have to be in order to withstand the pressure.

And that's the reason we don't build balloons filled with vacuum. If you fill a balloon with, say, helium, the pressure inside is equal to one atmosphere, same as on the outside. Yet, helium can still be lighter than air at the same pressure. So the balloon itself can be very thin and light. Vacuum, on the other hand, has to be contained within a thick, strong shell, or it won't be able to withstand the outside pressure. There is no material in existence that would be strong enough yet light enough to make a vacuum balloon.

That said, it's not a complete impossibility. It is possible to build a honeycomb structure with something like Mylar skin that can, in principle be buoyant due to contained vacuum. I don't know if anyone has ever actually built one, but I've seen some papers showing that it is possible.

At the end of the day, however, the advantage of vacuum being lighter than any gas is completely nullified by the weight of the container required to maintain said vacuum. It is always more efficient to use a light gas, such as hydrogen or helium. And with these you can, indeed, float to the very edge of space.

[Person012345]

Nope, it would more likely sink under the balloons weight because its filled with a vacuum. The reason a balloon shoots out of the water like that is because its full of air, and air is lighter than water, there is also the pressure of the water against the balloon and some other concepts I don't want to go into right now. A vacuum is the complete lack of gas or liquids, so there is literally nothing inside the balloon, except tiny amounts of space dust or whatever. They have several vacuum chambers at the NASA training center for vacuum testing, and these are basically big metal balloons and they don’t go shooting up into the air or even get light enough to float when the air is pumped out. Hopefully that covers it, but that's a pretty simple way to put it, hope I haven't offended any of the science buffs in this forum for simplifying it so much.

FYI, "nothing" is lighter than air.

So what K^2 said.

Edited November 15, 2013 by Person012345

[Adent]

Lets say the Displacement is large, much larger than the cost of the weight. Like a football filed of vacuum "volume"/size inside a sphere the weight of an 11x8 paper. It seems this would "float" on the boundary between space/atmo, displacement/weight. Orbital speed wouldn't matter as long as it holds its structure it will just kinda slide along the atmo.

I do realize materials and manufacturing of present couldn't come close to managing something like that, but I think if you could construct something that sized at a molecular lvl it seems plausible.

[dharak1]

As long as you have positive buoyancy you will float. I don't think that we know of anything that is strong and light enough to make a football field of vacuum. It would be pretty cool to make a floating city like that.

[qeveren]

I wonder if we'll start seeing vacuum balloons as our carbon-materials science improves.

[K^2]

Lets say the Displacement is large, much larger than the cost of the weight. Like a football filed of vacuum "volume"/size inside a sphere the weight of an 11x8 paper. It seems this would "float" on the boundary between space/atmo, displacement/weight. Orbital speed wouldn't matter as long as it holds its structure it will just kinda slide along the atmo.

I do realize materials and manufacturing of present couldn't come close to managing something like that, but I think if you could construct something that sized at a molecular lvl it seems plausible.

Unfortunately, the vacuum balloon problem does not scale at all.

Suppose, you have a vacuum balloon. You want to build one 2x larger. (Or 2x smaller.) This increases (decreases) buoyancy by a factor of 8, because volume scales as cube of diameter. This also, however, increases (decreases) the pressure it has to withstand by a factor of 4, all the while the cross-section has increased (decreased) by a factor of 2 only. Former is cross-section area of the entire sphere, which scales with square of the diameter, and later is cross-section of the shell only, which scales linearly with diameter. So now the shell has to be 2 times thicker (thinner). And because you already increased (decreased) total surface area by a factor of 4 already, the total weight of the shell has also increased (decreased) by a factor of 8.

So it doesn't matter how big or small you make that shell. The requirements of strength/weight of material from which you want to build it are the same. And it's impossible to build either way. Similar problem occurs if you consider how this changes with atmospheric pressure. If you reduce pressure, you can make the shell lighter, but you get less buoyancy by the same fraction. So again, the problem does not scale.

And like I said, materials with sufficient strength/weight to build a uniform shell that can maintain a vacuum and still be light enough to float do not exist.

[NGTOne]

Given current materials, yes, absolutely, a vacuum airship is impossible. However, as has been said already, a vacuum airship, IF IT WERE POSSIBLE, would represent the ultimate in displacement-based lifting power, far greater than helium or even hydrogen.

All that being said, though, it isn't inconceivable that, 20, 30, or even 50 years from now, someone will come up with a material that makes it possible, whether it's carbon nanotubes, spider silk (or some derivative), or something we haven't even thought of.

[Adent]

Regarding the outside pressure, if it was an absolute perfect sphere the pressure would be equal on the entire outer surface, like trying to crush and egg in a fully close hand. This would counter the need for mass to gain strength. Think of a material only a few molecules thick, and bonded together enough to not let any gasses in.

BTW, thanks for the brain food repliers!

[K^2]

Given current materials, yes, absolutely, a vacuum airship is impossible. However, as has been said already, a vacuum airship, IF IT WERE POSSIBLE, would represent the ultimate in displacement-based lifting power, far greater than helium or even hydrogen.

All that being said, though, it isn't inconceivable that, 20, 30, or even 50 years from now, someone will come up with a material that makes it possible, whether it's carbon nanotubes, spider silk (or some derivative), or something we haven't even thought of.

Doesn't matter. Materials that would allow a vacuum airship to out-perform a helium-filled one are not just beyond current material strengths, but beyond any theoretically possible material strengths. You will always do better by filling your air ship with a light gas than you would by trying to maintain a vacuum.

[Nibb31]

And even if you could lift a balloon above the atmosphere, it would have zero payload capacity, so what's the point?

Simply going up is useless. You want to be going sideways (fast!) to get to orbit, and you still need a pretty beefy rocket for that.

[K^2]

I wouldn't say completely useless. It could make for a pretty good replacement for comsats. In fact, if we didn't have satellites, we'd probably have some transmitters hanging on balloons 30km up. Satellites just work out to be more effective, and in the long term, cheaper than balloons.

[Nibb31]

Actually...

Google's Project Loon

Edited November 16, 2013 by Nibb31

[Kerbart]

Nope, it would more likely sink under the balloons weight because its filled with a vacuum. The reason a balloon shoots out of the water like that is because its full of air, and air is lighter than water, there is also the pressure of the water against the balloon and some other concepts I don't want to go into right now. A vacuum is the complete lack of gas or liquids, so there is literally nothing inside the balloon, except tiny amounts of space dust or whatever. They have several vacuum chambers at the NASA training center for vacuum testing, and these are basically big metal balloons and they don’t go shooting up into the air or even get light enough to float when the air is pumped out. Hopefully that covers it, but that's a pretty simple way to put it, hope I haven't offended any of the science buffs in this forum for simplifying it so much.

Whaaaaaaaaaaaaaaat?

I'd suggest reading up on the law of Archimedes and "Buoyancy." And by all means do go into some other concepts, you've raised my curiosity.

Out of curiosity, can metal ships float? Because metal is heavier than water?

[K^2]

Actually...

Google's Project Loon

There we go, then. And yeah, for internet, it makes more sense than satellites due to bandwidth crunch.

[NGTOne]

There we go, then. And yeah, for internet, it makes more sense than satellites due to bandwidth crunch.

Not to mention latency. Firing a signal up to GEO and back actually makes for a noticeable (by computers, anyways) increase in ping time as opposed to terrestrial fiber, because of speed-of-light delay and the limited throughtput capacity of the sat. Plus the transmitter power has to be a lot higher (part of the reason the Iridium constellation orbits so low - they're meant to work with satphones and other low-power transmitters, which would get lost in the background static by the time the signal hit GEO).

[Winter Man]

A vacuum aerogel would be quite easy, although I think with the mass of the gel itself we haven't managed to get one much lighter than air yet.

[NGTOne]

A vacuum aerogel would be quite easy, although I think with the mass of the gel itself we haven't managed to get one much lighter than air yet.

This year, an aerogel using graphene clocked in at 160 g/m^3, about 0.13x the density of air at sea level.

[source]

[magnemoe]

This year, an aerogel using graphene clocked in at 160 g/m^3, about 0.13x the density of air at sea level.

[source]

however for this use it must be either be used for an filler for an balloon or better have a lots of cells with air so an damage don't destroy it.

Doubt it would be cost effective to an balloon with hydrogen.

Anyway, it would just take you to the edge of the atmosphere, might a bit over if it was build aerodynamic and you managed to get decent speed on the way up.

See hooliganlab balloons for an excample of this effect, however you would need something serious massive to get more effect than dropping it at a plane where you can drop 20 ton or more from 12 km at close to the speed of sound with existing systems. You could build an plane to drop heavier load, another option is to put an rocket engine on the plane to take it higher and faster before releasing it.

[Kryten]

This year, an aerogel using graphene clocked in at 160 g/m^3, about 0.13x the density of air at sea level.

That's density of the lattice itself, ignoring air inclusions. To actually get that density you'd have to pump out the air, which'd result in the lattice collapsing if done at pretty much any level of positive pressure.

[drakesdoom]

A vacuum balloon will not work on the ground because the pressure will collapse any structure that is light enough to let it be buoyant. The question then becomes at what altitude if any can an extremely light vacuum chamber not collapse. Could you transition from either a hot air or hydrogen balloon on the ground to a vacuum balloon at altitude?

[K^2]

The question then becomes at what altitude if any can an extremely light vacuum chamber not collapse.

None. Because buoyancy also decreases with altitude, so you have to make the chamber lighter, and no pressure can the chamber be both light enough to float and strong enough not to collapse.