"The Transporter III is the largest transporter and has an enormous loading capacity" - I think, will be better, if we can do choice of the resources' order of loading - instead always: Uranium, Copper, Ore, Coal !? - as sample, I wanna and make the choice: Ore, Uranium, Coal, Copper (i.e. be able to change resources' loading order for every attack). With this condition, I would prefer the Transporter II with 8x speed :)

What's about the Explorer III? -- also faster!! ;)
and, maybe, with player's customized ratio lost/found for every explorer's launch - If I'll set more % chance to lost the explorer, then % chance of planet's founding to upping too (but slower of first %, of course)

Good luck to you - making this game better!