Soap bubble lunacositudiness

[defaultdotxbe]

My suspicion is that without air resisting the compression of the bubble, that a bubble formed in a vacuum would just compress itself into a drop of liquid.

yeah, i guess it would depend on how the liquid behaves on its own (if osmosis/diffucsion/surface tension/gravity/etc would cause it to collect into a drop)

my thought was, a bubble exists because the air pressure inside equals the pressure outside, and in a vacuum both pressures would be 0, so it can acheive equalibrium

of course its all hypothetical since im pretty sure creating the bubble requires some sort of pressure differential, which wouldnt exist in a vacuum

 

[Anti-sophist]

my thought was, a bubble exists because the air pressure inside equals the pressure outside, and in a vacuum both pressures would be 0, so it can acheive equalibrium

My guess is there's more to the equilibrium of a bubble than this. My suspicion is the air pressure inside is ever so slightly higher than outside, because it needs to cancel out of the surface tension of the bubble which would pull it together. I suppose the same argument can be made for gravity, as well, although that particular effect is many orders of magnitude less.

 

[maccy]

http://scienceworld.wolfram.com/physics/Bubble.html

 

[R.Mackey]

Can a soap bubble even exist in a vacuum?

No. The bubble has air on the inside. In a vacuum, it would instantly burst, since there would be no air pressure outside the bubble balancing that on the inside.

If you reduce the pressure inside and outside equally, in the limit of a vacuum, the bubble fails because the water content of the soap film skin will dissociate into the rarefied air.

If you redo the above situation but have a film that remains liquid in the limit of low pressure, then the "bubble" will eventually collapse into a droplet, as governed by surface tension.

If you have this miracle film and very, very carefully adjust pressure such that the film is held taut by a tiny amount of air inside, you will wind up with a lightweight, brittle structure that flies ballistically, just like anything else in a vacuum.

To be pedantic, one might consider inflatable space structures as a limiting case of the bubble in space, but as should be obvious, the "bubble" is a far sturdier structure than mere soap film.

 

[T.A.M.]

No. The bubble has air on the inside. In a vacuum, it would instantly burst, since there would be no air pressure outside the bubble balancing that on the inside.

If you reduce the pressure inside and outside equally, in the limit of a vacuum, the bubble fails because the water content of the soap film skin will dissociate into the rarefied air.

If you redo the above situation but have a film that remains liquid in the limit of low pressure, then the "bubble" will eventually collapse into a droplet, as governed by surface tension.

If you have this miracle film and very, very carefully adjust pressure such that the film is held taut by a tiny amount of air inside, you will wind up with a lightweight, brittle structure that flies ballistically, just like anything else in a vacuum.

To be pedantic, one might consider inflatable space structures as a limiting case of the bubble in space, but as should be obvious, the "bubble" is a far sturdier structure than mere soap film.

That was my point with the vaccum comment and the wink afterward...lol. Where would it get the surface tension to keep it expanded.

TAM

 

[Loss Leader]

To be pedantic, one might consider inflatable space structures as a limiting case of the bubble in space, but as should be obvious, the "bubble" is a far sturdier structure than mere soap film.

I'm a huge fan of inflatables for use as outbuildings on the moon or Mars. I'd still want my astronauts sleeping in hard-sided double-walled buildings, but the garage, greenhouse and even some temporary labs should be tents.

 

[R.Mackey]

They're actually more valuable in space. On Moon in particular, the incredible cold of the two-week long Lunar night, not to mention radiation, make sturdier structures a must for human habitation. Flexible structures are likely to break and leak, and offer little protection for astronauts.

The best use of inflatables in human exploration, my opinion, are cases where an extremely large volume is desired, say for the years-long journey to and from Mars. Pack that big ball with air (actually a honeycomb of chambers in all likelyhood, allowing compartmentalization) and hang out in the center, giving you lots of room to move and repair your spacecraft while also affording you some radiation protection through sheer distance of light elements.

Other, more near term uses of inflatables, are to pop open large structures -- antennas, booms, great big solar panels and mirrors -- at the lowest weight penalty. This is something NASA has been after for years, and starting to become practical, as my link shows.