The space trains cannot use the "Vehicle Fuel" fuel category that Krastorio 2 introduces. The mod also removes the acceleration bonus from vanilla fuels and introduces a penalty to most of them. Because the trains are so fast it isn't really a problem but it feels out of place to refuel them using "less processed" fuels.

I just released an Update that should fix it, if there are no further problems I'll mark this thread as fixed in 36h (starting 20/02/2023, 13:35 CET)

Great, thanks for the quick update!

You’re welcome

It would still be nice to be able to use some other advanced fuels, eg Plutonium fuel

Still a good mod :)

I'll see what I can do, but I'm not sure if one entity can use two different types of fuel (ie vehicle-fuel for normal fuel and nuclear-fuel)

I'm not the most knowledgeable about modding so take this with a grain of salt but in my save the normal trains can use the normal fuel and the vehicle fuel and I'm pretty sure I've seen other entities capable of taking multiple types of fuel in other mods.