These images feature a prominent foreground (whether it be a realistic landscape or some sort of sci-fi planet) with a background depicting planets, starfields, or other space relevant objects.
I know some strategies but I don't get how you make those realistic and sharp-contrast illustrations like the Mas Colony, do I just have to master the waccom tablet? I guess there's 3-D modeling too, but I don't know how you'd turn that into an illustration either.