SU will go pretty big, but I'm not sure if it will go that big, you may need to scale it as Jean suggests. Of far more importance is the fact that if you were actually to make the planets to scale with the interplanetary distances you would never be able to zoom in on them. They would simply disappear as you approached them, due to a phenomenon known as clipping.
Think of it as a depth of field issue...in order to accomodate a model that's a few billion miles in diameter, the closest you would be able to approach any particular object would be a few million.
If you make a 'compressed' version as seen in most solar system diagrams, this wouldn't be a problem...although you still probably wouldn't be able to zoom down onto a planetary surface sufficiently close to see a moonbase, for example.
