Ringworld options

absalomdraconis wrote:
>
> Take a long rope, and stick a weight to each end, then send one weight
> towards the sun, and the other away from it, making sure that their
> collective center of gravity is orbiting fast enough to keep from
> falling into the sun, and slow enough to stay in the same orbit.
> Because the weight closer to the sun isn't moving at orbital velocity
> for it's position, gravity tries to pull it towards the star, and
> because the other weight is moving too fast for it's position, it'll
> try to fly away from the star. Anything on trhe two weights will
> experience the same forces.
>
> Therefor, by building two ring structures, fastening them together,
> and rotating them so that their collective center of mass is at
> orbital velocity, you can have two ringworlds without needing the
> stuff Niven's ringworld is built of.
>

Niven's Ringworld surface orbited its sun at 770 miles per second, to
produce ~~ one gravity of "centrifugal" force on its inner surface. That's
the reason the Engineers had to invent scrith -- basically, to keep
Ringworld from stretching under its operational forces.

If you built a Ringworld and did not spin it rapidly, you'd need a lid to
keep all the air (and inhabitants) in. The small amount of centrifuge
effect generated by a two-level ring spinning at the orbital speed of their
collective center of mass wouldn't do the job, seems to me. And people
living on the inner ring would have hot feet, because gravity would have
them standing with their head away from the sun.

To compare with Ringworld's spin speed, orbital velocity for Earth is about
18 miles per second.

Steve