Also, all these man made satellites have position keeping thrusters, to
compensate for things like the moon. I have no idea as to what would
happen to this "ring" if they suddenly just turned them all off, but I
don't think anything major would happen very fast.

I've changed my mind about 20,000 km as a *safe* perigee height, as it
will endanger geostationary satellites orbiting in a constellation at
35,700 km.

If the perigee of the asteroid's orbit is 40,000 km and say the apogee
is 200,000 km then that may be a safe option. If the apogee goes much
above 250,000 km then there's the Moon's perturbing influence to worry
about, since it orbits at around 380,000 km.

Great, now all I need to do are some 'back of the cigarette packet'
calcs that show the Delta-V requirements to achieve a capture.

I hope no one gets too alarmed by all this... it's just some fun
calculations over a fun idea, which may or may not come to fruition
one day (depending if there's public support).

Abdul