I thought wood was too easy and undermined the entire idea of a fuel system. When wood outperforms uranium, something is off. However, without wood, people are finding coal unsatisfactory. The basic issue here is that , with the current setup, if the late game fuels are worthwhile, then the early game fuels end up being painful, which means that early game exploration is hindered, which is a problem. But if you make the low tier fuels cheap and easy to get, then the high level fuels become pointless. My proposed solution is varying spatial densities between sectors. First, traveling to planets within a star system only takes 1 fuel, as it is now. This is easily done, even with coal, and gives you some room for initial exploration easily. Next, traveling to planets within the first sector costs ~20 fuel. Its not trivial, but you can still stock up on coal and use it to get around and explore without it being unduly expensive. As your progress through higher level sectors, you are travelling our towards the edge of the galaxy, and the start's are less dense, so it takes more fuel to move between them. So, coal becomes a bbigger hinderence, but you have better tools to get it, and higher quality fuels start becoming available. Other arrangements could be done. One possibility is a scarcity issue: most worlds are level 1, a few are 2, a scattering are 3, and rare ones are 4... The consequence is that you will always have low level planets nearby that you can jump to cheaply. One level 2 planet may be nearby, but to start exploring multiple ones requires a higher fuel expenditure to deal with the increased distance. Similarly, level 3 planets are scattered further apart, and so it takes even more fuel to move between them, and so on. Over the course of the game you will go from poking around at a few planets nearby, to jumping across large spans of the galaxy between noteworthy planets. The main drawback is this doesn't mix as easily with the current structure of bosses which act as gateways to the next tier of stuff. In either case, escalating fuel costs can allow early game exploration to remain viable which encouraging the use of higher tier fuels as they become available.
