I think that one of the reasons that Earth doesn't have a ring system is because we have a moon - one that is relatively large when you compare that of Earth's to all others in proportion. Even in LEO corrections need to be made on a regular basis to account for the Luna's gravitational pull, which is enough to shift our own oceans - quite significantly in some places!
As for how it would have affected astronomy... I think that with such a large reflective surface so close to the Earth, it may have advanced a bit more quickly.
As for how it would have affected astronomy... I think that with such a large reflective surface so close to the Earth, it may have advanced a bit more quickly.