On Wed, 05 Jul 2006 09:01:50 -0600, in a place far, far away, Joe
Strout made the phosphor on my monitor glow in such a
way as to indicate that:

Suppose you have a large space station (OK, let's say a colony) with a
rotating portion and a stationary portion, both pressurized, and with
constant traffic back and forth between them. Obviously you need a
large mechanical seal between them, and I have some questions about that
which I hope someone can answer:

- In general how likely is this to be a problem? Suppose we want a
corridor 20 m wide between the two portions -- how much bigger is that
than any seal we've built before?

Unknown, but I don't see any theoretical problems.

- How can I estimate the leak rate through the seal?

Depends on design. I see no reason it couldn't be designed to zero
leak.

- Can I characterize the problem only by the pressure difference between
the inside and outside? In other words, is a seal that holds 1 ATM
against a vacuum the same as one that holds 2 ATM against 1 ATM?

In terms of the basic mechanics and strength requirements of the seal,
I'd think so. The issue is that there may be problems on the vacuum
side from material sublimation or welding. Not to mention radiation
(and perhaps monatomic oxygen, if it's in a suitable
environment--e.g., LEO). Just off the top of my head.

- What type of seal would you expect this to be? Radial shaft?
Labyrinth? Rotating face?

Rotating face would be my first choice, but again, just off the top of
my head. Think of a giant (hold breath) O-ring. Just don't do it in
January. You'd probably heat it, particularly on the space side,
though rotisserie effect might ease the issues..