Transition from pressurised envoronment to vaccum environment

[Ryan_m_b]

@Ryan: Don't you think it'll be good if an autonomous system catches them?! We had some cases where astronaut couldn't find the airlock door or couldn't ingress the airlock!

Ah I see, I thought you meant that a suit port specifically would need one. As for floating away a tether would be useful.

 

[Travis_King]

@Travis: So we try to come up with an idea to both lower the power and cost needed and lower the air loss!

The thing is, if you want to reduce power, you have to do it slowly (reallllly slowly if you also want to drop the pressure as close to vacuum as is practical). They already do this because you can't just take an astronaut, whose body is at 14.7 psi, and throw him in a suit that's pressurized to ~4.5 psi. He would most likely suffer decompression sickness (the bends). So they slowly drop the pressure in the crew cabin (or equipment cabin) to acceptable levels. They can drop it even futher after that, but that would mean hours sitting in a space suit waiting for the room to decompress. (unless, of course, you wanted to use a big heavy motor/pump and use up a great deal of precious energy).

For a larger scale station, with a great many space walks, it might be practical to invest in this (although one would imagine the number of flights coming to replenish supplies would be numerous enough to take care of lost air), but for something like this it's not really worth the time and money.

 

[armin11]

Dear Travis, I'm thinking about a large scale station and in it the tiny bit of air and oxygen are important! We don't have much available sources in long distance trips for example to mars,to produce needed oxygen for daily use so we must get the best of the available air, so we don't want to lose even the tiniest oxygen molecule! What I understand from your post is that you say we build larger pumps with greater efficiency. Is that right? But if astronaut goes directly in his suit we won't have the problem of waiting for the room to decompress.

 

[Travis_King]

It's a very nice idea, and certainly a problem for longer treks, as you pointed out. But here's the problems

1. The energy required to pump the room down to near vacuum means a larger, heavier pump/motor. This means heavier deadweight, thus more fuel required, plus less space. But this isn't the main problem, especially on so-called "Large scale stations".

2. The big problem is the time it takes. What are you gaining by waiting in the suit inside the room while the air pumps out? An average person uses approximately .5 Liters of air per breath at normal conditions. (and at standard psi, its somewhat less at the 4.3 psi suit pressure, though somewhat higher in O2 concentration). But let's say .5L per breath. Thats roughly 7.5 L of air per minute, 450 L per hour.

They already spend nearly an hour decompressing down to the nominal suit pressure (after several hours decompressing down to the ~10 psi I mentioned before) So you would need to balance between the air used just waiting versus venting the 5psi compartment. You waste both time and air depressurizing the compartment, whereas you can vent the air you would lose waiting anyway and spend the time and oxygen on something worthwhile.

I haven't done any of the calculations, but I'm going to bet it's either close, or it's deemed more valuable to have them outside breathing oxygen, than having the astronauts sitting inside wasting that oxygen in an attempt to save air that is mostly nitrogen.

 

[armin11]

Thanks,nice points! I've thought about donning suits in higher pressures like 8 psi and then until we reach the destination lowering pressure for the dexterity, but there are constraints in suit materials I think. What do you suggest for breathing oxygen outside?

 

[Danger]

Where are you getting this notion that that sort of technology exists or even is anywhere near usable?

You and Mech seem to be the only ones with an understanding of the difference between reality and fiction.
As a (former) writer of both, I did posit a high-efficiency airlock (actually a launching tube/hangar for a space-worthy fighter plane). My thought is that one could have a large space specifically devoted to air removal from a smaller space. As a land-based example:
Let's say that the airlock is represented by a 30cc vial. That is connected by tubing to a 50cc syringe with the plunger at the bottom. Pulling the plunger tries to remove 50cc of air from a 30cc volume, which should result in a good approximation of vacuum. At the conclusion of that effort, a sealed container would then be opened, which would result in chemical adsorbtion of a large percentage of whatever air is left.
I don't know specifically how effective that would be, but it would have to be better than an non-existent forcefield.

edit: It seems that several posts have appeared while I was composing this. That's what I get for PFing and watching Big Bang at the same time. I'll read the rest during the next commercial.

 

[MikeBH]

I am afraid the 30cc to 50cc idea only reduces the pressure from atmopsphere to about 400 milli-Torr. That is still high pressure not really an approximation to a vacuum. A vacuum pump needs to take it down at least 1:1000 to 1:100000. That means the plunger would be bigger than the ship.

 

[Danger]

I am afraid the 30cc to 50cc idea only reduces the pressure from atmopsphere to about 400 milli-Torr. That is still high pressure not really an approximation to a vacuum. A vacuum pump needs to take it down at least 1:1000 to 1:100000. That means the plunger would be bigger than the ship.

Well, for the purpose of the book, I didn't specify the size of the evacuation chamber. The "ship" is 8 stories high by 52 acres in footprint. Again, though, that is strictly fiction, and was just a grade 10 English composition project that got out of hand. (For those of you keeping track, that was 40 years ago.)

 

[MikeBH]

I am a plasma physicist so I decided to look at the idea of using a plasma window or more accurately a beam driven ion wind to keep the air from leaving the airlock. Just like the Star Trek idea. The system would work like this. An ion beam would be formed at the door of the airlock and directed at the air lock. The door would open but the beam needs to stay in place. There are a few ways to achieve this. The door could move back and the astronaut exits to the side between the door and the space craft.

The energy flux of 10^25 molecules per m-3 towards the 2 m^2 door at room temperature and atmospheric pressure is about 16kJ per second. This is the energy flux the beam most meet to keep the gas in the airlock after taking into account losses in plasma formation,

The ions will hit the gas atoms in the airlock and some energy will be transferred into momentum change in the gas. This produces an ion wind and a pressure that keeps the air in the airlock. There will be some energy lost in ionisation and and excitation of the gas forming a plasma. Let's say 16% of the beam energy is converted into momentum change in the gas for a 1kV beam, (this would be helped by charge exchange). I need about 100A of beam to prevent the air leaving. Problem is that is a lot of power 100kW and the plasma formed would heat the gas making it very hot also how do I create a beam at high pressures? So it doesn't work well at atmosphere.

However as we lower the pressure by a factor of 10 or 100 the current required scales down. At 1A the plasma beam power is only 1kW, This would not be a problem.

So we could pump down the airlock using a mechanical pump until the pressure was 1000Pa, then turn on the beam and open the door. The beam or indeed the plasma would not be a problem as the powers are quite low. Forming a beam at 1000 pa should also be possible. The gas temperature may rise but given the low pressure the heat transfer is small. We would have to increase the beam current to compensate for rises in the gas temperature. Need to check that does not run away.

So it is feasible to have a non-equilibrium (cold) beam driven plasma window to prevent air leakage at low pressure. How high in pressure we could go with this window is not clear - may be near to atmospheric pressure with some clever design.

 

[armin11]

Thanks MikeBH,very good, but I have some concerns.What is your opinion about these:
1. 1000 Pa equals about 0.3 psi, but our suit operates at very low pressure which is 4.3 psi, so lowering the room pressure to 0.3 psi would need great deal of time and power. This power loss added to the power needed to generate plasma field and later cool down the air would take great amount of precious power.
2. Wouldn't plasma filed put the astronaut's health at risk of some diseases or something else?

 

[MikeBH]

Ok the astronaut would put on his suit and and seal the airlock before the plasma is switched on. The plasma will create ozone and other radicals that would harm him if he inhaled them. The plasma is on while the door is open, only a short time so that the power needed is small. 1kW for a few minutes. 4.3 psi would require 10-15kW and might be possible. But it might be easier to use a simple mechanical pump to reduce the pressure or indeed the idea of a larger volume at vacuum opening to reduce the pressure. However in this case you need to pump the gas back into the craft anyway. Physics means you get nothing for nothing.
The plasma radicals are short lived so that after a few minutes the air retruns to normal and the sealed airlock can be open.

 

[Travis_King]

I still don't get how the astronaut gets out...

 

[MikeBH]

astronaut goes through the plasma beam front and exits to side of beam sources. Also possible to have opening between two beam sources.

 

[armin11]

So what you're saying is we need to exert force to the air molecules on the exit segment of the airlock . So why don't we use some high pressure air at the exit instead of plasma?wouldn't it be easier?I think it would require less power and less time to prepare!what do you think?!

 

[MikeBH]

Hi Armin11, The principle is the same. However creating a high pressure air jet only gets the energy upto a limited value. The air velocity at the exit of a jet engine is 500m/s. The velocity of a 1000eV beam is 2.5e5 m/s. As the energy goes as the velocity squared each molecule in a beam will have 100,000 more energy than in a air jet. So it takes a lot less beam gas to exert the force on the air molecules. So you would need a lot of gas flow if you use an air jet, this is a problem as the gas can escape. With the beam you use a lot less gas and it is more efficient.

 

[armin11]

Thank you Mike B Hopkins for all the effort,but I'm not satisfied with what I wanted yet.I think a mechanism that acts like jelly and astronaut can get inside it is better anyway. Don't you think?

 

[Travis_King]

A jelly that is stiff enough to resist the pressure differential from inside and outside the craft, yet jelly-y enough to let an astronaut pass through it?...

 

[armin11]

Yes,also we can put it in one place with the use of magnetic field.Is there some kind of material that can act like jelly in vacuum?

 

[Ryan_m_b]

Gels are made from polymers in water. You can make them stronger with higher densities of polymer, longer polymers and cross linked polymers. Problem is if you make it tough enough to withstand the atmosphere of the inside of the station an astronaut won't get through. Worse in space the water would just boil off and you'd be left with (at best) an aerogel.

 

[armin11]

Isn't there some kind of material that can act like gels but isn't composed of water?

 

[MikeBH]

Hi Armin11, I like the plasma solution as I am a plasma physisist. But I am also a practical guy so I think you are right the airlock without any air is the best solution. You suggest a gel to replace the air. I think this should be a gel inside a flexible but impervious outer surface so like an inflated ballon. It does not really need to be gel. The astronaut makes his way through a surface between the two inflated ballons. The ballons are touching making a vacuum seal but the astronaut separates only part of the seal as he moves through. Because the surface touches the astronauts suit, no air escapes as she move through.

 

[armin11]

Hi Mike, I've thought about the inflatable structure outside the airlock, but I think the power used to depressurize the space between the balloons is much more than the airlock and the time to do that is so high.
Dear Ryan_m_b your comment put an idea to my mind. What if we don't make the gel stronger with the use of polymers instead we make it stronger with the help of magnetic field that keeps gel in place. Next stage is getting through this gel. You said if it gets dehydrated it turns into aerogel. So we keep the condition for the gel cold, so it won't get dehydrated at first. Once the astronaut gets into a pile of gel we vaporize the water at the back of astronaut so gel turns into aerogel and no air gets out, so astronaut can get out from the other side. when the mission is complete and astronaut wants to get back we insert water into aerogel or some other work to make the aerogel soft again so astronaut can get in easily. Isn't this possible?

 

[armin11]

Gels are made from polymers in water. You can make them stronger with higher densities of polymer, longer polymers and cross linked polymers. Problem is if you make it tough enough to withstand the atmosphere of the inside of the station an astronaut won't get through. Worse in space the water would just boil off and you'd be left with (at best) an aerogel.

What is your opinion about my previous comment?

 

[Ryan_m_b]

Dear Ryan_m_b your comment put an idea to my mind. What if we don't make the gel stronger with the use of polymers instead we make it stronger with the help of magnetic field that keeps gel in place.

I know of know mechanism by which this would work. You still aren't going to keep the water in place.

Next stage is getting through this gel. You said if it gets dehydrated it turns into aerogel. So we keep the condition for the gel cold, so it won't get dehydrated at first.

Temperature is not the problem, pressure is. Even if the gel freezes to ice that's not going to help.

Once the astronaut gets into a pile of gel we vaporize the water at the back of astronaut so gel turns into aerogel and no air gets out, so astronaut can get out from the other side. when the mission is complete and astronaut wants to get back we insert water into aerogel or some other work to make the aerogel soft again so astronaut can get in easily. Isn't this possible?

I'm not sure what you mean here. Aerogel is a porous solid, its the complete opposite of what you want as it would allow air through but not an astronaut.

 

[armin11]

I'm not sure what you mean here. Aerogel is a porous solid, its the complete opposite of what you want as it would allow air through but not an astronaut.

I understand that there are more than fifty different kinds of aerogels, so you are saying there is none of them that is not porous and is impervious?!

 

[Ryan_m_b]

I understand that there are more than fifty different kinds of aerogels, so you are saying there is none of them that is not porous and is impervious?!

An aerogel is a gel that has had it's water removed leaving just the frame. You possibly could make one non-porous by compressing it or adding some kind of coating but you might as well call that a composite material.

Either way how does making a non porous and impervious material help you with your problem?

 

[armin11]

Either way how does making a non porous and impervious material help you with your problem?

If when the astronaut gets into gel, we turn the back segment of the gel into aerogel,the segment which is in the airlock,then no air is lost!

 

[Ryan_m_b]

If when the astronaut gets into gel, we turn the back segment of the gel into aerogel,the segment which is in the airlock,then no air is lost!

So your proposed idea is:

1. A segment of the wall of the vehicle is made from non-pourous (i.e. air tight) aerogel
2. As an astronaut approaches this segment the side nearest to them becomes a gel
3. Pushing themselves forward the areogel in front turns to gel and the gel behind back to aerogel

Is this correct? Assuming it is here are my problems with each point

1. Can a non-pourous aerogel be built that is suitable material for the wall of a space vehicle?
2. I am unaware of any method of turning an aerogel back into a gel, especially in the manner described
3. Assuming you could do this when the outer aerogel is converted back into gel it is structually weakened and the water in it will boil away in the vacuum before freezing

Those are quick points off the top of my head but I'm fairly certain there are other, big problems with this proposal as well.

 

[Travis_King]

It's cheaper to waste the air. On big ships just have robots/vehicles to the work. Like the deep sea subs. If you need someone inside it fine, just drop on in, you have a tiny air lock between the vehicle door and the entry port, very little air wasted. If you do need to step outside, deal with the few cubic feet of air lost...

 

[armin11]

So your proposed idea is:

1. A segment of the wall of the vehicle is made from non-pourous (i.e. air tight) aerogel
2. As an astronaut approaches this segment the side nearest to them becomes a gel
3. Pushing themselves forward the areogel in front turns to gel and the gel behind back to aerogel

Is this correct? Assuming it is here are my problems with each point

1. 
   
   Yo got the idea right! Though it has many problems and flaws, I think it can be feasible!It is great idea for my course project! For turning gel into aerogel we use some CO2,is that right?