Re: any limits on mechanical seals?

In article <1152565206.144921.242990@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Alex Terrell <alexterrell@xxxxxxxxx> wrote:
2. As well as people, you need to transfer fluids (water, air in,
carbon dioxide out), and electricity, and data. Data can probably done
with laser links between the two sections. Electricity with very large
commutators. Fluids are difficult...

Data you can definitely do optically or by microwave. Power can go by
commutator, by rotary transformer (a transformer with one winding on each
side of a narrow air gap), or even by microwave beaming. Fluids are a bit
more challenging, but there are ways...

Notably, consider a car tire: it has a U-shaped cross-section, and holds
air because the ends of the U are sealed to the central wheel. A tire is
fixed to its wheel, but with suitable seals, it could rotate while the
wheel was held stationary.

As I suggested earlier, build the joint between rotating and stationary
sections as a pair of concentric cylinders, say the rotating one outside
and the stationary one inside. The passageway is through the middle; the
annular space between the cylinders is where all the engineering is
located -- bearings, seals, etc. Most of the engineering hardware is
fixed to the outer cylinder, and slight pseudo-gravity is available there
because of the rotation. The stationary inner cylinder "rotates"
overhead.

Consider a trough, open side facing inward, running all the way around the
engineering space, fixed to the outer cylinder, mounted overhead on struts
so people and equipment can pass under it (it's the "tire"). Its upper
edges seal against the inner cylinder (the "wheel"). Blow air into it
from an air duct opening into its bottom, and pull air out of it through a
duct opening out of its top, and you can pass air from one section to the
other. Add another such assembly to pass air the other way. (The ducts
are *not* concentric cylinders -- just ordinary square-ish ducts at a few
places around the circumference -- so they don't have any problem going
around each other.)

Similar setups will work for water, pressurized gases, even sewage -- just
make sure the seals are good. :-)
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