>Also, the turtle the move the space shuttle on moves vewwy vewwy slowly,
Top loaded speed 3mph, AFAIR. I think NASA keep it down to 1mph most of the time just because it's a little safer and they're in no rush to get anywhere.
>along a very flat surface.
Actually it has to climb quite a steep ramp at the launch pad. Or do you mean flat as in lack of lumps and bumps rather than gradient? It certainly wouldn't like to roll over any rocks along the way, but the main problem is that the shuttle would topple over, not that it couldn't do so; if it was carrying something with a much lower center of gravity it could probably take it over quite rough ground with those huge tracks and all that power.