Spacecraft Depressurization question

[Guest MetroCognit]

Hi all, this is my first post, and I hope you won't mind me taking the time to throw a fistful of questions out there concerning the effects of air loss aboard a spaceship. Though I am beginning to write a story that entails a Sci-fi setting, I can't claim to be a physics genius myself, but neither do I know if anyone has ever actually pondered what I ponder...

 

I was wondering whether it would be catastrophic for a spacecraft to lose all or the vast majority of the air into space, not just in terms of what happens to the unfortunate passengers, but how that might affect the actual structure of the ship. Would it be something that destroyed the craft, or severly damaged it, or would the structure maintain integrity? What might happen as the air loss, and the accompanying loss of pressure, progressed? Would it depend on what materials the spacecraft was made from?

 

How about objects aboard, obviously anything not tied down would be sucked out, but how might objects that are fixed be affected? Would their fixtures be affected? If any hull breach was not closed in time(let's say, for a long time), how might the temperature of space treat them? Would they freeze, become brittle?

 

In addition, would the force of the escaping air have any effect on bodies already in space? I.e. if there was a solid object in front of, let's say, the airlock, and it opened, also inadvertantly allowing the air of the ship to escape, would the object be propelled backwards by the force of the air? would the air have enough force to push the object before it froze into ice crystals(as I am fairly sure would happen)?

 

I hope you find these questions fun to think about, and that I actually do get answers to them I would be very grateful for any help you guys gave me, and I offer you my thanks in advance.

 

MetroCognition

[5614]

the space ship, assuming is built well, should stay in tact

 

if objects are properly and well attached to the main structure, they should remain there, although loosely held items would be sucked out.

 

if the airlock was opened and something was blocking it, the object would be blown away, slowly...

 

remember that once things start moving, they tend not to stop for a while due to lack of friction.

[[Tycho?]]

It should not effect the structural integrity of the ship itself, unless the ship used pressure from the air inside the ship to maintain its shape. Things inside the ship not tied down would be moved, the air rushing out of the ship would be moving quite quickly, so a large hole could suck out even pretty heavy objects as long as there was enough air inside to push it out.

 

In a lot of sci-fi movies and tv shows, a big hole gets torn in the side of the ship, and the crew members valiantly hold on to something while the air is sucked out. If say an entire wall of a room was ripped out, all the air in the room would be gone in a couple seconds, and you could not be able to hold on with muscle alone.

 

As for the effects on the objects inside the ship, depends on what they are. Organic things would not fare too well, plants or animals dont do well in close to zero pressure and temperatures in the tripple digits below zero.

 

As for the objects outside the airlock being propelled, well yes they would. If a large hole opens in the ship a big chunk of atmosphere would quickly rush out. It hits the objects inside, which sucks them out. Say a person right outside the door would be pushed back as the air hit him. The air would not however turn into ice cystals. Any water in the air would, but the air itself would not. It would escape from the ship, and very quickly disperese to a very very low density.

 

If you need more detail or have more questions feel free to ask.

 

Oh right i almost forgot. When air is escaping from the vessle, remember that the vessle would be pushed back. Probably not a lot since the vessle would be signifigantly more massive than all the air contained within it, but it would be enough for at least a minor course correction.

[Guest MetroCognit]

Your answers have helped me out a lot! I think I should, though, give you a little more detail about the kind of spacecraft I had in mind.

 

Are any of you familiar with Gerald O'Neill, and the space habitat designs he proposed? I have a story I'm working on that's set aboard an Island Three, which is a huge space colony, about twenty miles long and four miles in diameter, enclosing a huge interior space. The inside is divided up into three windows and three land strips, each of which feature 'Earth-normal' landscapes, meaning greenery, buildings, towns, the idea being to make life on board as pleasant as possible. They're basically countries in space. Please take a look at the pictures below, for a better idea of what I mean.

 

The size would probably affect the rate of air loss, and the time it took to lose it all. In my story, fairly big holes are blown in the windows by entities who don't wish to actually harm the inhabitants(it's just that they regard complete air loss as an acceptable way of achieving their goal), whom take shelter in large buildings that double as pressure shelters.

 

Given the size, I think it is unlikely that the air would be lost all at once, as the windows are not broken completely. But would loss of pressure affect an Island Three differently than regular spacecraft? And what problems might the 'pushing back' phenomenon cause for the habitat(which is linked to another habitat, to prevent it from skewing from it's orbit)?

 

I probably could find a place devoted to discussion of these kinds of space habitats, but to be honest I'd be embarrassed to ask about this sort of thing there, I'd probably come across as someone who was only interested in how these habitats could be destroyed. So to avoid offending the enthusiasts, I thought it prudent to ask in a more neutral place.

 

Thanks again for all your help, and I hope you continue to find my questions of interest.

 

MetroCognition

 

 

An Island Three habitat as seen from outside.

 

 

The inside of an Island Three habitat.

[[Tycho?]]

Your answers have helped me out a lot! I think I should' date=' though, give you a little more detail about the kind of spacecraft I had in mind.

 

Are any of you familiar with Gerald O'Neill, and the space habitat designs he proposed? I have a story I'm working on that's set aboard an Island Three, which is a huge space colony, the size would probably affect the rate of air loss, and the time it took to lose it all. In my story, fairly big holes are blown in the windows by entities who don't wish to actually harm the inhabitants(it's just that they regard complete air loss as an acceptable way of achieving their goal), whom take shelter in large buildings that double as pressure shelters.

 

Given the size, I think it is unlikely that the air would be lost all at once, as the windows are not broken completely. But would loss of pressure affect an Island Three differently than regular spacecraft? And what problems might the 'pushing back' phenomenon cause for the habitat(which is linked to another habitat, to prevent it from skewing from it's orbit)?

 

I probably could find a place devoted to discussion of these kinds of space habitats, but to be honest I'd be embarrassed to ask about this sort of thing there, I'd probably come across as someone who was only interested in how these habitats could be destroyed. So to avoid offending the enthusiasts, I thought it prudent to ask in a more neutral place.

 

Thanks again for all your help, and I hope you continue to find my questions of interest.

 

MetroCognition[/quote']

 

 

I'm afraid I'm not familiar with that sort of design. Most large space vessles would probably be built with air locks connecting several air-tight compartments. So a hole in one area would just cause doors to close, so only that area loses its atmosphere. Of course, it could be the craft is designed with lots of open areas or something, so this may not be possible.

 

The size of the craft wouldn't effect it more or less as far as I know. If its more massive, it just means that more atmosphere has to be lost to move it.

 

As for the stability of the craft, I guess it depends on how massive it is and the mass of atmosphere lost. I dont know how fast air escapes due to de-presurization, otherwise I could do some example math for you. If you can look up how fast the air escapes, and you have the mass of the habitat and the volume of air, you can figure out exactly how much the habitat will move as a result.

 

For your purposes, the effect would be minor, and wouldn't cause it to fly off and hit some planet or something. Unless you lose a ton of air it would not cause any short term problems, only the need for a minor course correction at some point.

[Thales]

The size would effect it as a large pressurised area with a small hole will depressurise much more violently than a smaller area with a large hole. The example that comes to mind is again aircraft. If the hole in the fuselage is large enough there is not as significant amount of 'pulling' due to air loss as there is if the pressure is being lost through a smaller hole.

 

If the air is lost through a smaller hole(not too small of course) I would imagine it would destablise its orbit to a greater extent as it would act almost like a miniture thruster.

[swansont]

The size would effect it as a large pressurised area with a small hole will depressurise much more violently than a smaller area with a large hole. The example that comes to mind is again aircraft. If the hole in the fuselage is large enough there is not as significant amount of 'pulling' due to air loss as there is if the pressure is being lost through a smaller hole.

 

If the air is lost through a smaller hole(not too small of course) I would imagine it would destablise its orbit to a greater extent as it would act almost like a miniture thruster.

 

I don't think so. The pressure difference is fixed (e.g. 1 ATM inside, ~0 ATM outside). The force is proportional to the area of the hole. Smaller holes exert less force.

[atinymonkey]

I'd be less concerned about the exit of the air and more concerned about the damage to the superstructure. The depressurization would cause microfractures in the areas surrounding the windows which would compromise the integrity of the hull. Even in a massive ship, the loss of air by itself could be coped with if the damage could be repaired. The ship should contain kits near all vulnerable areas for sealing them off or repairing depressurized compartments, and the lost air should be replaceable via reserve tanks. However, the expulsion of the air could cause the microfractures to spread to bulkheads. I suppose the loss of oxygen would make ark wielding simpler, if it could be useful, but there would have to be an awful lot of work before the area could be pressurized again. In some respects, massive decompression would be preferable to slow violent decompression. The crew could even be forced to manually depressurise the evnviorment outside pressure shelters in order to stem hull damage.

 

I suppose if your writing a story, you have to remember the will have procedures and drills for dealing with the situation. They may even have self sealing hatches around vulnerable areas, like simple window shutters that the force of depressurization would pull shut over the window. The attackers could just break one window at a time, some air would escape from each before it sealed itself.

[Thales]

But swansont if the force is exerted over a shorter amount of time on a massive body it will find more resistance to a change in momentum than a slow gradual release that provides a constant push, no? Isn't it a question of impulse not nessercaily total force?

[swansont]

But swansont if the force is exerted over a shorter amount of time on a massive body it will find more resistance to a change in momentum than a slow gradual release that provides a constant push, no? Isn't it a question of impulse not nessercaily total force?

 

The impulse is force * time. A larger hole gives a larger initial force but for a shorter period of time. So it will depend on how long it takes to "exhale" and you need to integrate the force over the whole time to see the total change in momentum.

 

 

But that's not what I was responding to. You said that a small hole will depressurize more violently, and that's not right. The mass flow rate should depend on the are of the hole and the pressure differential. The flow rate, and force, should initially be smaller for the smaller hole. It should also take longer to depressurize for the smaller hole (longer time constant for the smaller hole - I suspect both will give an exponential decay, which implies infinite time to completely depressurize. But one would use the "five time constants" approximation)

[Thales]

The impulse is force * time. A larger hole gives a larger initial force but for a shorter period of time. So it will depend on how long it takes to "exhale" and you need to integrate the force over the whole time to see the total change in momentum.

 

If the force is function of the pressure differential and that is fixed regardless of the hole size then doesn't it hold that integrating the impulse over a longer time will yield a greater change in momentum?

[Guest MetroCognit]

atinymonkey, would microfractures be more of a danger to spacecraft that produced gravity(or artificial gravity) by rotation, as O'Neill space habitats do? As in, would the microfractures end up tearing the ship apart acting with the forces generated by revolution?

 

Also, would these microfractures only affect metallic materials, or all materials? The reason I ask is because Island Threes would have the metal on the outsides coated with rock derived from asteroids, to protect the people inside from radiation. There is even talk of constructing habitats from concrete instead of metal, to avoid the habitats 'bursting' if there was a hull breach. Would a habitat made from concrete be subject to microfracturing, if there were a breach?

[RICHARDBATTY]

You could have expanding foam contained in small pockets in the walls. If the walls were punctured it would self seal. Just a thought. A long sustained release of atmoshere through a smaller hole would give a greater movement than a short release through a large hole. Think of a car with 95bhp 11sec 0 to 60 to halve the acceleration time you have to go up something a lot bigger like 400bhp so it is more efficient to have lower acceleration over a longer period. The occupants would have gases disolved in their blood at 1 ATM and under rapid decompression this would boil out of their blood. It would allmost certainly cause swelling and blood lose through the nose and perhaps eyes/ears but how much I'm not sure. I think exploding crew members might be a bit over board but its possible.

[swansont]

If the force is function of the pressure differential and that is fixed regardless of the hole size then doesn't it hold that integrating the impulse over a longer time will yield a greater change in momentum?

 

The initial pressure differential is fixed, regardless of area

 

The force is pressure * area

 

A larger hole gives you a larger initial force, but it won't last as long

[Thales]

Thats my point it won't last as long and therefore won't yield a substantial shift in momentum when compared to a more prolonged push.

[swansont]

Thats my point it won't last as long and therefore won't yield a substantial shift in momentum when compared to a more prolonged push.

 

Won't last long but the force is large. For a small hole, it lasts longer but the force is small.

 

You have to solve for F(t) and integrate over the duration to see which has a larger effect.