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WestAir

Liquids that don't boil at 0 ATM.

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Google has failed me. Every search just discusses water.

I'm making a sci fi and I'm trying to come up with a unique, but possible, way to handle airlocks on celestial objects with no atmosphere for large objects like ships or rovers. This is what I came up with:

Lunar-Landing.gif

My problem is that I don't know what liquid can stay a liquid at 0 ATM, but also won't be corrosive to a ship or explosive if RCS thrusters are fired at it for landing or lift off. Obviously the pool can be kept heated or cooled to an ideal temperature.

Any help would be great. Thanks!

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Probably, none of them, as both gas and liquid don't have any crystallic structure, their molecules are moving chaotically, so some of them will escape the surface.
And even solid bodies are sublimating.

Also the pressure inside the Space Port will push the liquid down and then outside, into the vacuum.

So, only some kind of sci-fi magic is required.

Edited by kerbiloid

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There aren't any liquids that like to stay liquid in a vacuum. However, there are a few that can handle pressures pretty close to it. For example, under fairly reasonable temperatures mercury can take anything over 2 billionths of a standard atmosphere. That puts it well in range of keeping happy in the atmospheres of Triton, Pluto, and possibly even Io on occasion.

This table will be of interest to you:

https://en.wikipedia.org/wiki/Triple_point#Table_of_triple_points

Looks like ethanol works pretty well, too.

You could have a special engineered material in your sci-fi world that works better than any of these, too.

3 hours ago, kerbiloid said:

Also the pressure inside the Space Port will push the liquid down and then outside, into the vacuum.

Maybe if you didn't keep the whole pool liquid, but just the part around the ship you could stop this from happening. Create a sort of 'bubble' for the ship to pass from the outside in.

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2 minutes ago, cubinator said:

Maybe if you didn't keep the whole pool liquid, but just the part around the ship you could stop this from happening. Create a sort of 'bubble' for the ship to pass from the outside in.

Ice.

Melt through the ice.

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28 minutes ago, kerbiloid said:

Ice.

Melt through the ice.

Yep. But you could even make it ice that wouldn't even boil off when melted if you used one of those materials with a low triple pressure. (If you were on a world with a thin atmosphere, that is.)

Edited by cubinator

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Or just have a roof over the pool that keeps it closed when the other side is exposed to vacuum.

Thanks Cubinator! I was trying to engineer a hard sci fi solution to the problem of big Star Wars / Star Trek like spaceports being ridiculously impractical to pressurize/depressurize. I wanted to go with a more natural airlock that didn't need hours of time, required huge pumps, and had no fail-safe for if the power went out. Doesn't look like I'm smart enough for the task, though. -_-

Edited by WestAir

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2 minutes ago, WestAir said:

Or just have a roof over the pool that keeps it closed when the other side is exposed to vacuum.

Thanks Cubinator! I was trying to engineer a hard sci fi solution to the problem of big Star Wars / Star Trek like spaceports being ridiculously impractical to pressurize/depressurize. I wanted to go with a more natural airlock that didn't need hours of time, required huge pumps, and had no fail-safe for if the power went out. Doesn't look like I'm smart enough for the task, though. -_-

I would suggest that submerging your spacecraft in a liquid is not a great idea, as ideally they will have just enough structural strength to not collapse under their own weigh in their expected operating environments.

If they need to resist external pressures greater than 1 atmosphere(aka parity with the inside), then they need to be much stronger against crushing pressures(like a sub) as opposed to just containing pressure(like a balloon).

If you are going to submerge it under multiple tons of mercury(a ton of mercury is about 18 gallons, so you would need a lot of tons for a pool to submerge a space ship). it will need a lot more structural strength to prevent being crushed, making your ship a lot heavier than it would otherwise need to be.

 

Why not just keep most ships in an unpressurized dock(possibly with an airline-style pressurized walk-way) and only bring them in to an air-dock when they need massive repairs?(sort of like a navy dry-dock)

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You can get around atmosphere pushing the medium down by having the inside be lower than the outside. The pressure head of the liquid on the exterior side will resist the push of the atmosphere on the inside.

If ethanol is almost as suitable as mercury it would be a far better choice from a hull pressure point of view. A 5m tall vehicle would have approx 10atm of pressure at the base of the hull in a pool of mercury, but only about 1.5atm in a pool of ethanol.

Add 1atm internal pressure and that becomes 9barG Vs 0.5barG.

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3 hours ago, WestAir said:

Or just have a roof over the pool that keeps it closed when the other side is exposed to vacuum.

Thanks Cubinator! I was trying to engineer a hard sci fi solution to the problem of big Star Wars / Star Trek like spaceports being ridiculously impractical to pressurize/depressurize. I wanted to go with a more natural airlock that didn't need hours of time, required huge pumps, and had no fail-safe for if the power went out. Doesn't look like I'm smart enough for the task, though. -_-

Looks like ethanol should work here, perhaps butanol works even better or it might freeze, however you can control the temperature here. 
You probably want some cover on the inside too because of fire hazard and fumes, you don't want the ones maintaining spaceships being drunk all the time on work after all :)
But ethanol is nice in that its not very toxic, people drink it after all and its commonly used for cleaning but you are still dipping your spaceship in it it will typically have lots of dead space and hot surfaces. 

This would work best if you have an stream of smaller crafts needing servicing all the time, fighter jets is an good example. Large crafts would not be put in an atmospheric hangar outside of dry dock maintenance and that would be easier in zero-g. 
Guess you would also just want to dock commuter crafts but you might give them an bath if they needs servicing or unloading larger cargoes. 


Love this out off the box idea, Note that I would probably want an roof attachment point instead. 

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Looks like an "Oxygen Not Included" Liquid lock. 

 

Although....   If that door is elevated some above the ground, so the shuttle has to drop vertically down a small shaft, the pressure in the hangar shouldn't be able to push the liquid up over the top of the shaft.    There's some height H that the force gravity will overcome the force of the air pressure inside the hangar.    Although....(mk2)..... that would cause a 50-75% depressurization (guessing) inside the hangar as the volume suddenly increased, bursting everyone's eardrums and causing various sorts of other barotrauma. 

So anytime the the lock gets utilized, you'll have to evacuate the hangar, and seal it off from the rest of the base.   And then you'd have to wait for the liquid to subliminate enough inside the shaft to restore equilibrium. 

Mercury might be dense enough to not cause the massive displacements though.   But now everything is covered in a toxic liquid metal. 

Edited by Gargamel

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I was speaking with someone who works at a company that uses Ferrofluid as the seal for vacuum chambers among other things. While my knowledge of this type of material is extremely limited, the fact it is used for applications at zero atmosphere suggests using ferrofluid could accomplish your airlock concept.

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My limited knowledge of physics has the very definition of boiling as some kind of equilibrium between the gas above the fluid and the fluid itself. Which is why adding more heat to a boiling fluid doesn't raise the temperature but just maies it evaporate faster.

If the pressure of the gas is higher than the equilibrium requires, the fluid will not boil. That seems to be a problem with vacuum for your solution.

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14 hours ago, Exploro said:

I was speaking with someone who works at a company that uses Ferrofluid as the seal for vacuum chambers among other things. While my knowledge of this type of material is extremely limited, the fact it is used for applications at zero atmosphere suggests using ferrofluid could accomplish your airlock concept.

Yeah, this seems like the best solution. Failsafe would be sliding blast doors.

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On 12/29/2019 at 12:41 PM, Terwin said:

I would suggest that submerging your spacecraft in a liquid is not a great idea, as ideally they will have just enough structural strength to not collapse under their own weigh in their expected operating environments.

If they need to resist external pressures greater than 1 atmosphere(aka parity with the inside), then they need to be much stronger against crushing pressures(like a sub) as opposed to just containing pressure(like a balloon).

If you are going to submerge it under multiple tons of mercury(a ton of mercury is about 18 gallons, so you would need a lot of tons for a pool to submerge a space ship). it will need a lot more structural strength to prevent being crushed, making your ship a lot heavier than it would otherwise need to be.

 

Why not just keep most ships in an unpressurized dock(possibly with an airline-style pressurized walk-way) and only bring them in to an air-dock when they need massive repairs?(sort of like a navy dry-dock)

The main reason I'm abandoning traditional airlocks is for uniqueness. In todays world of storytelling, more of the same is just boring. If a butanol or fermifluid airlock can get a whole cargo / passenger shuttle into a pressurized hangar,, using real world physics, then I'd be pretty happy.

As for pressurization concerns, as RCgothic and Magnemoe stated, I might be able to get away with a 0.5 atm crushing pressure using ethanol. Not great, not terrible.

On 12/29/2019 at 4:48 PM, RCgothic said:

You can get around atmosphere pushing the medium down by having the inside be lower than the outside. The pressure head of the liquid on the exterior side will resist the push of the atmosphere on the inside.

If ethanol is almost as suitable as mercury it would be a far better choice from a hull pressure point of view. A 5m tall vehicle would have approx 10atm of pressure at the base of the hull in a pool of mercury, but only about 1.5atm in a pool of ethanol.

Add 1atm internal pressure and that becomes 9barG Vs 0.5barG.

Thanks for the math. As for the atmospheric pressure push into the vacuum, I think I can get around this by just having airtight seals on both the vacuum and hangar sides of the pool, opening one at a time to allow transport of the shuttle, and both sides closed when the airlock is not in use.

On 12/29/2019 at 4:50 PM, magnemoe said:

Looks like ethanol should work here, perhaps butanol works even better or it might freeze, however you can control the temperature here. 
You probably want some cover on the inside too because of fire hazard and fumes, you don't want the ones maintaining spaceships being drunk all the time on work after all :)
But ethanol is nice in that its not very toxic, people drink it after all and its commonly used for cleaning but you are still dipping your spaceship in it it will typically have lots of dead space and hot surfaces. 

This would work best if you have an stream of smaller crafts needing servicing all the time, fighter jets is an good example. Large crafts would not be put in an atmospheric hangar outside of dry dock maintenance and that would be easier in zero-g. 
Guess you would also just want to dock commuter crafts but you might give them an bath if they needs servicing or unloading larger cargoes. 


Love this out off the box idea, Note that I would probably want an roof attachment point instead. 

Thanks Magnemoe!

I wonder, since water is heavier than ethanol, I wonder if I can't just have the pool be made of water, and the ethanol floating on top of the side where the roof is vacuum. That way ships get a nice bath on their way out of the dusty vacuum and workers don't get drunk off of fumes.

22 hours ago, Gargamel said:

Looks like an "Oxygen Not Included" Liquid lock. 

 

Although....   If that door is elevated some above the ground, so the shuttle has to drop vertically down a small shaft, the pressure in the hangar shouldn't be able to push the liquid up over the top of the shaft.    There's some height H that the force gravity will overcome the force of the air pressure inside the hangar.    Although....(mk2)..... that would cause a 50-75% depressurization (guessing) inside the hangar as the volume suddenly increased, bursting everyone's eardrums and causing various sorts of other barotrauma. 

So anytime the the lock gets utilized, you'll have to evacuate the hangar, and seal it off from the rest of the base.   And then you'd have to wait for the liquid to subliminate enough inside the shaft to restore equilibrium. 

Mercury might be dense enough to not cause the massive displacements though.   But now everything is covered in a toxic liquid metal. 

Never played Oxygen Not Included. I had to look it up. That game looks pretty fun.

As for the barotrauma, do you know if having only one side of the pool open at any one time (with the other sealed airtight) would eliminate the concern completely? That way the air in the hangar never has a chance to push the water, ethanol, or ferrofluid into vacuum and no need for digging longer shafts?

20 hours ago, Exploro said:

I was speaking with someone who works at a company that uses Ferrofluid as the seal for vacuum chambers among other things. While my knowledge of this type of material is extremely limited, the fact it is used for applications at zero atmosphere suggests using ferrofluid could accomplish your airlock concept.

Awesome! Now ferrofluid's are easily magnetized. Will RCS thrusters / electronic components / solar flares make the pool dance out of its tub?

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2 hours ago, WestAir said:

Thanks Magnemoe!

I wonder, since water is heavier than ethanol, I wonder if I can't just have the pool be made of water, and the ethanol floating on top of the side where the roof is vacuum. That way ships get a nice bath on their way out of the dusty vacuum and workers don't get drunk off of fumes.

Awesome! Now ferrofluid's are easily magnetized. Will RCS thrusters / electronic components / solar flares make the pool dance out of its tub?

In my experience water and ethanol mixes well, I want an sponsored study on this together with some experienced bartenders and liquids who has been stabilized for an long time :)
You might use some heavy oils on the outside as they float well. However this make you lift off like an bird in an oil spill.
Benefit of ethanol both moonshine and for cleaning substance is cooling and evaporates. 

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Not sure where people get the idea that ethanol would be good in this application.  Sure, it has a low freezing point, but it offsets that with higher vapor pressure -- that is, it evaporates.  There isn't a low density liquid with low vapor pressure, sorry to say.

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19 minutes ago, Zeiss Ikon said:

Not sure where people get the idea that ethanol would be good in this application.  Sure, it has a low freezing point, but it offsets that with higher vapor pressure -- that is, it evaporates.  There isn't a low density liquid with low vapor pressure, sorry to say.

Yes, it evaporates easy, high proof ethanol feel very cold on the hand as it evaporates fast, much colder than water. 

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https://en.wikipedia.org/wiki/Plasma_window

You probably want a *very* big capacitor bank, but with a plasma window you can do what you're describing above. Ship/Rover/Dude/Space Monster arrives, plasma window turns on, doors open, Ship/Rover/Dude/Space Monster enters, doors close, plasma window goes off.

Or if you have a good enough energy source, you can just keep the plasma window on indefinitely, and only turn it off and close the door properly when you're not expecting any traffic.

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17 hours ago, WestAir said:

Awesome! Now ferrofluid's are easily magnetized. Will RCS thrusters / electronic components / solar flares make the pool dance out of its tub?

Solar flares wouldn't hurt anything. 

My thought, to make it work properly, would be to have the spacecraft land on a rugged platform similar to a car lift. The platform would be mounted on articulated arms that would then pull the spacecraft through the forcefield.

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Ferrofluids, however, have similar problems to mercury, in that they consist of magnetic micro- or nano-particles suspended in a liquid such as oil -- the magnetic particles increase the density of the oil (though it's still less dense than mercury).   Also, the oil will evaporate in a vacuum, though this process is slowed by the magnetic particles (reduced surface area and adsorption bonding).

That said, you could actually get away with some external pressure -- after all, your spacecraft are pressurized internally.  There's no actual compression on the hull until external pressure exceeds the internal pressure.  A ferrofluid twice as dense as water could be thirty meters deep on the Moon before it reaches that pressure.  Even mercury could be more than five meters deep in 1/6 G before it reaches 1 atm.  Now, getting that much mercury to the Moon is a problem left as an exercise.

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There are ionic fluids which have very low vapor pressures. However, I have no idea how corrosive they are or is there other problems with spacecrafts diving in them. But in fictive story there can always be assumptions that "this special material can hadle that liquid"

Also, I do not know would it be more practical to use exotic chemicals or more common, like water or ethanol, and accept some evaporation losses during use. In any case such liquid air lock sounds very fictive and not practical at all.

 

https://en.wikipedia.org/wiki/Ionic_liquid

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Liquid air locks are used routinely in some settings.  A "moon pool" in an oceanographic ship (used for launching ROVs and occasionally crewed deep submersibles) is one sort; the swim-in entrances in saturation dive habitats are another (there was a good depiction of the latter in several scenes in The Abyss).  In both cases, pressure at the water surface is the same as pressure at the same height outside the structure -- but there is pressure present, so the liquid (water, in every working case I know of) doesn't just boil off or evaporate.

 

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why not use extremely fine powder instead

slightly magnetic so they stick together

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