The 2nd and 3rd habitat spheres for the Enzmann Lance Star Ship model are identical. ( 2 REQ'D) So just this one model needs to be ordered twice. (You will need two in order to make the ship correctly.)
The 2nd and 3rd habitat spheres include the appropriately placed nuclear reactor housings, from which comes heat that creates steam that turns the turbines that power generators. The dual purpose thermal radiators that will use the Sebeck effect to generate power while radiating away the waste heat generated in the nuclear reactors.