Island One, Two and Three

From: Saatvik Agarwal [mailto:asaatvik@....uk]

> Could you guys please explain what are the effects of torque
> which you've been talking about?

When O'Neill was designing his first habitat (O'Neill Cylinder), he
quickly realized he had a problem. His design was dependent on the
habitat pointing continuously at the sun. But since the cylinder was
rotating, that made it a gigantic gyroscope. Gyroscopes tend to keep
pointing in one direction relative to the stars. Which means that a
single rotating cylinder would circle the sun like the pedal of a
bicycle when what was needed was for it to circle like the spoke of a
wheel.

O'Neill realized that he could solve the problem by having not one but
two cylinders of equal masses rotating in opposite directions. From an
angular momentum point of view, the two momentums cancel out and the
connected pair has 0 net angular momentum. Thus there's no problem with
the pair continuously turning to follow the sun (at the rate of about a
degree a day at our distance from the sun). There is a modest force
trying to turn each cylinder relative to the other. This can be
countered by a cable under tension at one end, and a tower under
compression at the other end. But these are relatively modest forces.
The cable would only be about the diameter of a teacup, and the tower
would be comparable to a radio mast.

Other habitat designs came up with other solutions. In both the
Stanford Torus, and in this design
(http://www.ssi.org/assets/images/Ch06p088.gif), the habitat spins in
the same plane as the orbit, and a large, oval-shaped mirror tracks the
sun rather than the habitat itself. In the Bernal Sphere, the radiation
shield is set counter-rotating relative to the pressure hull so that the
overall structure has 0 angular momentum (and so can continuously point
at the sun). Since the shield is something in the neighborhood of ten
times the mass of the pressure hull and its interior furnishings, it
doesn't need to rotate nearly as fast.

Regards,

Mike Combs