it can work with a lot of effort i think and a large delay in transit. it would be similar to modern rail bridges and elevators. train comes to rest on first giant elevator. elevator goes down train darts forward to the next one that then rises up

I think your best bet for this kind of solution would be to have controlled and really strong top-to-bottom air-flow, similar to the one they have in cleanrooms used for semiconductor technology. If you direct the flow of air very heavily downwards, collect it in tubes at the bottom and then fan it back to the dome, you could get a system that might work for Mars (not for vacuum at one end mind you). Of course, a train moving at high speed would also affect air turbulence, so I don't know how it would interfere with the system.

I'm pretty sure that the pressure differential kills the idea - afaik, you couldn't maintain a pressure differential without an active system keeping the gas in place, and any pressure difference large enough to make a dome actually necessary is going to make the energy requirements unfeasable. On the other hand, if the pressure difference is low (the dome is there to keep out radiation, weather and so on), then I can't see any reason why this shouldn't work. Should there be no pressure difference, then it's questionable if you need an air lock at all - the CO2 rich martian atmosphere should be more dense anyway, so putting the exits below the internal ground level would make the dome act as a diving bell. What you could do is make a "revolving" airlock: the airlock is 100m (for example) long, and vehicles simply drive down it - mobile walls preceded and follow each vehicle allowing them to pressurize individually.

Chernoborg wrote:

GenUGenics wrote:

Also, check into plasma window technology, which for brief periods can act as a shutter between areas of different atmospheric pressures

In the past I've toyed with the similar idea involving a magnetic ferrofluid held in a field as a sort of liquid airlock.

Have you ever read Permanence buy Karl Schroeder? That kind of tech is used in a really cool way in that.

I think at this point, we need to apply the rarest superpower: Common Sense. All of these ideas have high-speed maglev trains barreling full-tilt into an inhabited city, through some kind of hilarious contrivance designed to act as a maglev-speed airlock. Any of the gas-pressure versions run into the risk that the system will fail, thus leaving a gigantic, train-tunnel sized hole in the dome's pressurization; not to mention the fact that a maglev train barreling into that high-density gas will create a shockwave in front of it and a low-pressure zone behind it, blowing whatever high-density gas you used into the dome, and creating a hole through the gas zone which will, if only briefly, connect the dome interior and exterior atmospheres. Also, you know, what with the pressure differentials, you'd have to be manufacturing and pumping a [b]lot[/b] of gas into the tunnel, constantly. The high-speed door systems that track with the train and both fill and "sweep" the entire tunnel are hilariously vulnerable to sabotage, and even a simple failure means the train is plowing headlong into the door, which will break the airlock and probably kill some folks. If you want to get a train from outside the dome to the inside of the dome, you just need to use a regular airlock, bring the train to a halt in it, and then go into the dome. People probably don't want a supersonic maglev train going through their city anyway, so you'll have to slow down one way or another. If you just want to get the people in the train into the dome, then you just pull up to a train station outside the dome, use extendible docking airlocks to the train doors, and they disembark to a terminal inside the dome, where they can then board the local transport taking them in the direction they want to go.