In article ,
Volker Hetzer wrote:

Joe Strout wrote:
Of course, *replacing* the O-ring, or otherwise doing maintenance on
this giant rotating seal, could be a real PITA. Certainly something to
plan for up front.
For maintenance you could start up the stationary part or stop the
moving part. Then you just put in a temporary inner seal and work
on the O-ring to your heart's desire.

Well, yeah, except that we're talking REALLY large parts here -- it
would take months to spin down the habitat, and the same amount of time
to spin it up again, during which your 10,000 residents are getting
mighty grumpy. Spinning up the stationary portion would be easier, but
may not be possible, as it wouldn't be designed to take the loads.

Or the connector consists of a tube with an O-ring on both ends, then
you can couple the tube either to the still or to the moving part and
always have one O-ring at rest relative to the tube and the connected
part. Then maintenance ought to be easy too.

That's an interesting idea. Seems to me it would double the leak rate,
and the failure rate, but it may be worth it for easy maintenance.

You can minimize leaks further by pressurizing the connection
only when needed.

I don't think so. Both modules are always pressurized, and there isn't
a lot of point to making the connection double as an airlock. Assume
the connection is needed pretty much constantly anyway.

Also, for long term survival I think that the air locks pose the bigger
problem. And accidents of course.

Could be, but one issue at a time please.

OTOH, earth loses a bit of air too (http://tinyurl.com/nxqqu) but during
the last few billion years it wasn't much of a problem, so, depending on
the size of your station, a few spoonful per day may be tolerable.

Quite so; I don't expect the leak to be a problem, but it should be
estimated and figured into the resupply needs.

Best,
- Joe