[Spaceships] Can't find the right propulsion system

[Kale]

You can use Smaller Systems to convert a single system into three systems of one size (SM) smaller: You can replace a 3G chemical rocket with a 1G rocket and two small fuel tanks, all one SM smaller than the ship. This gives 2/3rds the capacity of a full SM sized fuel tank. If you want to go really small, you can convert down by two SM levels and get 10 systems at SM-2 for a single full sized slot. Each rocket would provide 0.3G of thrust at that level.