I can't remember the exact quote or source, (it may even be in the SW) but Joseph Smith said angels live on a different planet from ours.

Also, why weren't "humans" (with robot assistance) prevented from going to the Moon, Mars, or beyond? I have doubts that God has placed a bound on where humans can go -- other than the ones of sheer space and the speed of light, which are natural ones of course.

To me it's like "closing off" the Americas from the mass of humanity for years. Man's own misguided ideas formed a "wall" around the old world in the middle ages. The means of getting there was always at their disposal, but their own beliefs (flat earth, etc.) were holding them back. Maybe this was his will (seems to be so from certain BoM passages), but eventually the New World was found.

Not long before that, Eutopeans explored central and southern Africa, and the far East, which seems to be the genesis for a unifying of isolated cultures; which according to the Bible were dispersed at Babel.

This might be taken a step further to planets with human-like life on them someday.