Obtainable Ringworld around the Earth?

Hi,

Have you read the 3 part article by Paul Birch,
"Orbital Ring Systems and Jacob's Ladders," in the
Journal of British Interplanetary Society (part I,
Vol. 35, pp. 475 ff (1982); part II, Vol. 36, pp. 115
ff; part III, pp. 231 ff (1983))? It gives a very
through explaination and all the needed physics. Plus
some other very interesting applications that are just
now starting to become of practical importance.

regards,
Dave

--- Lucio de Souza Coelho wrote:

> On 1/4/07, Xenophile
> wrote:
> (...)
> > Ah, I begin to see.
>
> That's good, because I still have no drawing. :)
>
> (...)
> > But if the the forces are to be balanced, and one
> > ring is moving much faster than the other, then
> the faster-moving ring
> > needs to be LESS massive than the slower-moving
> ring. How much less
> > massive? How Fast?
> (...)
>
> Well, lets put some numbers in an hypothetical case.
> Suppose a ring
> circling Earth at an altitude of 200Km
> (Shuttle/ISS-like altitude). At
> that altitude the outer, static ring would
> experience a surface
> gravity of around 0.93g. Then in order to counteract
> that gravity and
> produce 1g outward, the inner ring would have to
> spin at 11.2 Km/s .
> And the mass of the outer ring would have to be
> around 8% higher than
> that of the inner ring.
>
> Conversely, if you put the gravity of the inner ring
> also at 0.93g,
> then the outer and inner rings will have exactly the
> same mass.
>
> Another Ringworld-related problem that I forgot is
> dynamic
> stabilization. Since this structure would not be in
> orbit, behaving
> instead like a "solid" ring around Earth with the
> center of mass
> matching that of Earth, some portions of it could be
> slightly closer
> to Earth than the others; and as a result the ring
> would be
> irrevocably pushed toward Earth from some side and
> be destroyed. In
> order to avoid that, the ring has to be dynamically
> stabilized, ie,
> sensors have to constantly monitor if the ring is
> tending to "fall" in
> some point and push the structure a little bit
> accordingly. The
> obvious way to do such corrective pushes would be
> using giant
> thrusters, but since those are very inefficient I am
> thinking about
> something more elegant: magnetic attitude control.
> By using
> electrodynamic tethers, the ring could interact with
> Earth's magnetic
> field and use the forces thus obtained to keep
> itself correctly in
> place.
>
> Of course I have no idea of the order of magnitude
> of magnetic fields
> required by that. I would need restart the little
> knowledge of
> magnetism that I have...
>

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