> Except, of course, for the front part, which was weirdly aerodynamic
It could separate, so maybe it was intended to be able to handle entry into a planet's atmosphere as a lifeboat. It also looked cooler that way.
> Yes, the lack of fuel tanks is a real problem. Also, how do they fly? They only have engines in back, but they skim over the surface of the moon like they are levitating.
I don't remember if the show mentioned anything about it, but I'm sure the books said it used nuclear engines of some kind. The model I had as a kid had rockets on the bottom too, which would have been a very inefficient way to fly but maybe doable if it was nuclear.