I noticed that this has cropped up a few times before, but I really want a fuel system, so here it is again. I am thinking it could be some sort of ore, which has a fair chance of spawning in every asteroid. Each piece generates a certain amount of power before being consumed, depending on the reactor configuration. Some configurations would generate more power for their size, but also use more fuel for the amount of power generated. Others would generate less power for their size, but be more efficient with fuel. The raw ore could be used to generate power, but refining it is more efficient. Naturally, for people who would rather not have to mine fuel for their huge ships (understandable), it would be an optional config. I feel like this would add a bit more to the survival aspects of this game, for those that want it, as at the moment much of the resource management in singleplayer survival seems to just be waiting for factories to make enough of something and finding a shop that has what you are looking for.