Transition from pressurised envoronment to vaccum environment

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

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 vaccum pump needs to take it down at least 1:1000 to 1:100000. That means the plunger would be bigger than the ship.

Danger

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 physist 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 transfered 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. Lets 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 doesnt 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 feasable 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.