Suggestion: Use ion fuel before rocket fuel in spaceships when possible.

This violates expected behavior for an ion ship, and likely general desired behavior. It also seems odd to allow a spaceship to even use booster fuel if none of the relative engines are present (ion ship likely can launch from planet only with booster tank).

The main drawback here is the desire to use the ion fuel for operations, and rocket fuel is only present for a lander shuttle pod. The tank is much denser than normal storage tanks so it's not desirable to work around the problem by using the non booster tanks for fuel storage.