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I recently answered a question on Worldbuilding about space stations. In my answer, I proposed a toroidal station which would be composed up many small segments, each rotating. As was pointed out, this would require at least one an airlock between each of the wedges bookending each segment and the segment itself. The airlocks would have to rotate.

Do we have the current technology to build rotating airlocks? Have any designs been tested?

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    $\begingroup$ If all the sections rotate at the same rate, you could join the rigid sections with accordion-flex tubes (like a bendy straw or an articulated city bus). $\endgroup$ – Russell Borogove Nov 24 '14 at 1:30
  • $\begingroup$ @RussellBorogove Unfortunately, they don't all rotate at the same rate. $\endgroup$ – HDE 226868 Nov 24 '14 at 1:32
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    $\begingroup$ Not exactly ready for prime time yet but have you considered force fields? A wall of electromagnetically contained cold (hydrogen) plasma could confine atmosphere or anything with small momentum (mass times velocity) while being permeable by higher momentum objects such as an astronaut moving from one containment field to another. Also check How would a centrifuge module's berthing system work on the ISS? $\endgroup$ – TildalWave Nov 24 '14 at 10:33
  • $\begingroup$ You don't really need an airlock, you need a section that swivels while keeping atmosphere. $\endgroup$ – GdD Nov 24 '14 at 11:21
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I'd go with "yes, but"

There are two tricky parts: You need a large, gliding seal, and you need to build conduits for cables, pipes, etc. I'm not a mechanical engineer, so maybe I misrepresent a few things.

Google for largest axial face seal found this article about a seal at 390mm diameter .. that's not much. Admittedly, thiy is for a compressor where the pressure differential is far higher than what you'd find in a space station, so there may be hope. The challenges in building seals are in creating and aligning to very, very smooth surfaces. for a large seal hoop this means a large lathe and probably many headaches in transporting and installing. But I'd say it's doable if someone throws enough money at the problem.

The second challenge are conduits. We know how to transport fluids between rotating elemtents. The conduit would always need to be in the middle of the airlock, where it 'costs the most space (imagine the smallest circle you can fit a 1x1m cupboard through. now imagine the smallest circle you can fit said cupboard through if the center is blocked), compounding the problems with seal described above. You will also build your conduits once, retrofitting for more connections once they are built will be hard.
For electrical power, brush contacts are available, for signal transmission you'd probably use something wireless. Why do I talk so much about conduits? because you will want to move air, water, sewage, fuel and a host of of stuff from on segment to the other.

In summary, I think we can but we will have a hard time to interconnct the parts of the station in a meaningful way.

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  • $\begingroup$ Actually, the conduit wouldn't need to be right in the middle, but the "receiver ports" would need to be unreasonably large, running all the way around the airlock. $\endgroup$ – SF. Nov 24 '14 at 10:57
  • $\begingroup$ yes! I needed a sec to wrap my head around what you ment, but yes. $\endgroup$ – mart Nov 24 '14 at 10:59
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    $\begingroup$ imagine a ring of pipe (torus) cut in half length-wise - e.g. "inner" and "outer" half. Sealing that will be at least tricky, and the friction will be unpleasant, but it's possible, especially for unpressurized/low pressure media moving in one direction (centripetal force forcing them towards the "outer" side being the outlet). $\endgroup$ – SF. Nov 24 '14 at 11:03
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We can have rotating airlocks with current tech, but their durability and performance is rather poor (and of course the speed difference can't be too big.

The secret is making the airlock as two (or more) interlocking ("telescope") pipes, with grease in between; enough of greased overlay between the pipes so that its friction/viscosity makes air pressure insignificant. Of course the joint will leak, albeit very slowly, and so, must be refilled with grease, and of course the viscosity will put quite a bit of resistance against the rotation, so don't expect this to be a zero-loss joint between modules rotating at different speed.

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    $\begingroup$ It would be great to have source attribution $\endgroup$ – Everyone Nov 25 '14 at 12:29
  • $\begingroup$ The problem with this approach is one end of the grease is exposed to a vacuum and will evaporate over time. See the problems with wheels etc. on Moon/Mars vehicles. $\endgroup$ – Hobbes Dec 24 '14 at 12:14
  • $\begingroup$ @Hobbes: This could be overcome by constant (very slow) supply of fresh grease from the "pressurized" size. Grease that dries up gets pushed outside, replaced by fresh, at rate of it drying up. $\endgroup$ – SF. Dec 24 '14 at 20:48

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