On 3/12/2010 12:16 PM, David Spain wrote:
Pat writes:

To totally eliminate that effect at one g, you need something around the
diameter of the station in 2001.

Rather than a centrifuge, why not just spin the whole craft? That eliminates
bearings and vibrations (to some degree) and helps spin-stabilize the craft.
Also the entire mass of the spacecraft can offset small shifts in mass inside
the craft, eliminating the need for a high rim mass centrifuge to achieve the
same effect. Also it's not clear you need to spin to 1g when something smaller
might suffice and thereby avoid the coriolis effects on the inner ear at a
higher spin rate.

This of course puts some design constraints on the spacecraft and requires a
fair degree of axial symmetry. There are always trade-offs....

Then you've got the docking problem; you need a de-spun docking port,
you have to stop the spinning when you want to dock, or you do the 2001
trick and spin your spacecraft up to the same rotational speed as the
module.
You could put a de-spun section on one end of the module and use that to
hold the docking collar, solar arrays, and communication antennas (this
is done on a lot of communications satellites where the cylindrical
solar-cell-covered body spins for stability, while the antennas remained
pointing at Earth), but now you are spinning a large diameter airtight
seal between the two sections, and that's going to be difficult to
design from both a air leakage and no torque transference point of view.
To keep the centrifuge in balance you could use a vibration sensor that
detects it being off-balance and transfers some sort of fluid from one
side to the other to balance it out.
Another concept would be to not directly attach the centrifuge proper to
the module at its axis points, so that vibrations can't be transferred
from one to the other; it could either spin on a air bearing at either
end like a lot of gyroscopes do, or use a magnetic field to do the same
thing.
I'm really surprised they had such trouble with the ISS centrifuge
module, as this doesn't sound like a insurmountable problem to address
in its design.
One oddball problem would be that the centrifuge would act like a gyro
wheel and try to rotate the station as it orbited around the Earth.
Two counter-spun sections to it might solve that problem by canceling
out the gyroscopic effects.

Pat