Randal here, back for more Terraforming. I have previously discussed and created some asteroid based ideas/locations with goblins and dwarves to show off different ways in which asteroids can be just as useful in adventure creation. In both, I mention that...
When looking at creating a sci-fi fantasy sandbox, take a loot at how you would accomplish the feel you want in traditional fantasy, and then try ways to adapt that to space. Thus, dwarven mines become an asteroid field...