"Grimble Gromble" wrote in message news:bgaad.1897

Is there any particular reason that you'd want to build a planetary ring
other than inspiration from science fiction stories?

Time to own up... Yes that was *exactly* the inspiration! Although
creating a ring was never a sought after goal in my propsal, rather a
*desirable* side-effect from carving out my asteroid to build a
habitat within its interior.

I trust this hand-waving response will not irritate those who deem numerical
simulation to be the be-all and end-all of discussions (though I expect this
comment will).

Your hand waving in this instance makes sense. I have done my highly
intricate dynamical analysis and I hereby report that a ring system
that is not oriented along the Earth's equator, which is emanating
from a non-circular orbit of an asteroid, will scatter its particles
at the fastest rate, and no Earth orbiting ring system could ever be
formed in those circumstances. This is mainly due to the differential
rates of precession of each ring particle's orbital nodes owing to the
un-even (oblate) mass distribution of the Earth.

On the other end of the scale, a perfectly circular, concentric system
of ring particles orbiting exactly co-planer with the Earth's
equatorial plane has a very short term (a couple of years at most)
chance of staying together in a ring formation. That's assuming an
orbital altitude of 40,000 km above the equator. However, such a
particulate ring system is then subject to two kinds of external
perturbing influences: that coming from the Sun and that from the
Moon, acting along the ecliptic plane and the plane of the Moon's
orbit, respectively. The combined effects of both these forces will
cause the ring material to scatter into a 'band' of +/- 15 degrees
geocentric latitude (30 degree spread around the equatorial plane)
over several years...

The final conclusion is therefore no stable ring system would be
possible around the Earth in the long term, hence any excavation
debris carved out of an Earth orbiting asteroid will require serious
containment/safe disposal. Thus, such an orbital engineering project
is not going to be viable around the Earth.

That said, there is always a possibility of deploying a number of
robotic digging vehicles on the surface of an asteroid and performing
the excavation in-situ, in *its* orbit prior to summoning it to Earth
orbit. An advanced series of nuclear powered rovers, much larger and
with more 'clout' than the Mars rovers of today, could be despatched
onto the surface of a candidate asteroid where they progressively dig
their way into its interior. The mass reduction from such excavation
would make the task of subsequent transportation of the asteroid to
Earth that much 'lighter' and leave no scattering debris near Earth.

AAI