posted
A short story I'm writing requires that somebody open a loading bay door in space. Does anybody think that would be possible? What happens with pressure? Does pressure has to be equalized - does space have pressure? Any help would be appreciated.
Posts: 22 | Registered: Jul 2003
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posted
OK, the first question is whether the loading bay ever has air in it. That would depend on what kinds of things are loaded and unloaded in the bay. If at all possible, the lading bay would not have air in it, because every time you open the door to space, you will lose some air out the door, and the larger the bay is, the more air will be lost. (Note: this is true even if you depressurize the bay before opening the door, because it's pretty close to impossible to pump all the air out of the room.)
If the bay does have air in it, then there will most probably be systems in place to prevent the door from opening until the bay has been depressurized, in order to prevent a loss of air. However, there would probably be an emergency override that would allow the door to open anyway; this would be useful if there were a fire in the loading bay, because that would put out the fire.
However, there would also be a system in place to prevent the loading bay door from opening if the door between the loading bay and the rest of the [ship, space station, whatever] were open, because that could suck the air out of the whole place.
Assuming the loading bay door opened either by sliding or by swinging outward, the physical act of opening the loading bay door would not be difficult, because the pressure inside the bay is higher than the essentially zero pressure of space.
If the door opened inward (One reason it might open inward is for safety, since air pressure would tend to keep the door from opening until the bay had been depressurized. However, that would leave less usable space inside the loading bay, since there would need to be sufficient room for the door to swing open.), then it would be very dificult to open the door while there was still air in the bay. Air pressure at sea level is fourteen pounds per square inch (sorry, don't know the metric equivalent off the top of my head) and even if you assume that a space vehicle pressurized to a lower level, a door of any size is going to have a whole lot of pressure on it. Manually opening it would be next to impossible; it would require machinery to do it.
[This message has been edited by EricJamesStone (edited July 23, 2003).]
posted
Yes. It's possible. How you do it depends on what kind of tech you want to use. Here's some ideas.
You could use an airlock. It's a chamber keeping the vacuum of space seperated from the rest of your ship by two sets of heavy doors. Pumps evacuate the air in the chamber and repressurize it as you move things in and out.
Or maybe some sort of energy field that will allow solid objects to push their way through, but won't allow gases to pass.
If you have an organic-based tech, you might use a permeable membrane that "knows" what things can pass. Or maybe even has a sphincter-like opening that forms a seal around and object and pushes it in or out.
posted
Answer to your most basic questions: for all practical purposes, the atmospheric pressure of deep space is zero. There are a few stray atoms out there, but they come in contact with each other so infrequently that the pressure thus generated is insignificant.
No matter what the pressure in the bay was before the door was opened, after the door is opened the pressure becomes zero. You can think of the air atoms rushing out and trying to pressurize the entire universe if you like.
One excpetion you might consider: you could buils a bay that's like a planet. If there is gravity in the bay (assuming some pseudo-science mumbo-jumbo like in Star Trek or Star Wars) then the gravity will help hold air in. If the bay opens in the top, and the walls of the bay are a hunderd miles high, then you don't need doors at all. At the top of the bay is the vacuum of space, on the floor of the bay your would have enough air pressure for humans to be comfortable. This would be a bit like Niven's Ringworld.
posted
So, if a meteor crashed into a spaceship and the relative sizes of each were such that only a hole in the spaceship resulted, the ship would lose air and everyone would die, but the ship would remain intact other than the hole. In other words, no explosive decompression. Am I understanding that right?
[This message has been edited by Kolona (edited July 23, 2003).]
posted
Well, the air rushing out through the hole would probably drag loose objects along with it, but normal atmospheric pressure is low enough that the air rushing out is unlikely to cause more structural damage to the ship. (It would not be anything like the reverse situation, of a leaking submarine at great depth. At a depth of only 100 meters, the outside pressure is 11 times normal atmospheric pressure.)
posted
Kolona, I always though "explosive decompression" referred to what happens to your lungs, not your spaceship. I'm no expert on this particular term, but my guess is that it predates manned spaceflight. With what we know today, a better term might be "expulsive decompression."
The meteor crash scenario is the greatest fear of our manned space program. It's unlikely, but it's also unpredictable. As bad as it is, the movie Mission to Mars did present a relatively good depiction of a very tiny meteor hitting a spaceship. They're hard to detect because they're so small and relative velocity can be so great, possibly in the hundreds of thousands of miles per hour.
posted
In my opinion the best scenerio for the loading bay would be to have remote controled robots loading and unloading. This way you avoid the pressurezation or depressurezation of the bay all togather. No need for artificial gravity and you avoid all the problems. As a matter of fact I have used this myself as a way to avoid just these complications. i'm surprized you didn't come up with that one Doc.
Posts: 41 | Registered: Apr 2003
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posted
That is an interesting site, Eric. I've taken scuba training and, though I've dived only in quarries, I'm familiar with underwater pressure concerns, and I'm an airline disaster book and movie aficionado so I'm passingly familiar with atmospheric decompression. Decompression involving a vacuum like space, though, threw me a little.
Doc, there's definitely expulsion with explosive decompression, but it seems more a result rather than the defining feature. Something is expelled due to explosion of a container. As per the site Eric listed:
quote:"in general the action of being exposed to vacuum will also involve a rapid decompression. This event is generally known as "explosive decompression," and apart from the simple effect of vacuum on the body, the explosive decompression event itself will be hazardous."
Although I've never heard it put this way, could the opposite to explosive decompression be called implosive compression?
(I gotta end this posting already. )
[This message has been edited by Kolona (edited July 24, 2003).]
[This message has been edited by Kolona (edited July 24, 2003).]
[This message has been edited by Kolona (edited July 24, 2003).]
quote:One excpetion you might consider: you could buils a bay that's like a planet. If there is gravity in the bay (assuming some pseudo-science mumbo-jumbo like in Star Trek or Star Wars) then the gravity will help hold air in. If the bay opens in the top, and the walls of the bay are a hunderd miles high, then you don't need doors at all. At the top of the bay is the vacuum of space, on the floor of the bay your would have enough air pressure for humans to be comfortable. This would be a bit like Niven's Ringworld.
Heh... that's an amusing idea. Totally impractical for working on any realistic scale of course, but very cool nonetheless...
BTW: Niven has a word for what you call 'some pseudo-science mumbo-jumbo', which is 'bolognium'. I kind of like it :-)
posted
Jules's reply quoting Doc Brown got me thinking, and I won't put in all the steps that got me to this point, but could the following idea possibly work?
You have a launch bay with a pressurized atmosphere.
The entrance to the lauch bay from space is an area filled with ionized gas at a pressure slightly above that in the bay, but magnetic fields are uses to keep the ions from escaping into space or the launch bay.
Air from the launch bay would not escape into the ionized area, because the pressure there is greater than in the launch bay itself.
Of course, there would be all sorts of problems with actually bringing objects -- particularly ferromagnetic materials -- through the ionized area...
posted
Just off the top of my head, I don't believe that would work.
Consider the case of a membrane that is permeable to CO2 but not O2. Sandwich two of these together in your door space and fill the intervening space with O2. Then fill the loading bay with CO2 at a lower pressure and watch what happens. All your CO2 leaks out! What happened? It turns out that where you have a selectively permeable membrane the principle of "partial pressure" comes into play. The overall pressure doesn't matter, because only certain particles can pass through the membrane. So only the percentage of pressure supplied by those particles matters, and thus the CO2 leaks into the door area despite the higher total pressure because the partial pressure of CO2 is lower there. Thence it leaks into space, where both total and partial pressure are lower.
Of course, if you ionized all of the air in the loading bay, and then used a magnetic field to keep them from escaping...it would tend to work, but some air would still leak out because the constand exchange of electrons that would take place among ionized gas molecules would always leave a few molecules unionized at any given moment, and these would be able to escape across the magnetic field rather easily. Inceasing the degree of ionization would limit, but never totally stop, this leakage. There is also the small problem caused by the fact that humans cannot readily breathe highly ionized air, and the other problem of getting magnetic or electronic equipment through a powerful magnetic field without turning it off, as you have mentioned.
The only "force field" technology that has been demonstrated effective for dividing an atmosphere from a vacuum is a form of particle beam that creates a stream of high velocity particles forming a "curtain" over the opening. It has been demonstrated for small openings, but suffers from a couple of problems as well. A physical object trying to pass the particle curtain would occlude the curtain from extending to the side opposite the emitter, thus allowing the escape of air. Also, the bombardment of high velocity particles could burn or ionize some surfaces, so anything passing through would need to be specially shielded. The other problem is power consumption, this is not an energy efficient means of separating vacuum and atmosphere on a large scale.
My suggestion? Just leave the loading bay unpressurized, as others have suggested. You should only pressurize segements of your craft that really need to be pressurized.
Explosive decompression simply means that the decompression occurs in the manner of an explosion--that is, all at once in all directions. The velocity of the explosion depends on the actual pressure differential involved, but things will be flung about, rather as if there were an explosion. This is what creates the real hazard of an explosive decompression, things being flung about by the explosion. It is not otherwise more dangerous than gradual decompression, which is quite dangerous enough. Without air, you cannot breath, and you will die. Also, without an atmosphere, the liquid water on the surface of your body will rapidly evaporate, leaving only what is below the triple point in tempurature, that is, ice. This will be particularly hard on any exposed mucus membrane, meaning you will be blinded and rather uncomfortable. And of course your ears will pop, but they will probably not burst.
posted
Hey Survivor, I knew you when I lived in Virginia!
I'm not sure that partial pressure would matter to my idea, as the area with the ionized gas would not be selectively permeable to gases, as far as I can tell. But it's been twenty years since I took chemistry, so I could be wrong. And there must be some major problems with the idea, or someone would have done it by now.
posted
The problem is that the magnetic field bounding the ionized area doesn't stop ordinary gases from leaking through it. It only stops ionized gases. The only times an ordinarly gas molecule wouldn't penetrate the barrier would be if it happened to bounce off a ionized gas molecule that was in the process of bouncing off the magnetic field. This wouldn't happen too often with gases (though for separating liquids, your idea might actually work pretty well, depending on the solution chemistry).
Most of the time, an ordinary gas molecule would pass right through the magnetic field before bouncing off any ions, then it would bounce around until it found it's way out of the ionized gas region. But there is no way to determine, once it has entered the ionized area, whether it will exit towards the loading bay or towards space.
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