I wanted to win a science victory right after winning a cultural victory. To win a science victory, I have to build a bunch of spaceship parts and move them to my capital, where they are assembled. Thing is, I can't stack units, so either the spaceship parts can't move to the capital if there is another part there, or they just switch spots. Is this normal, or it is a bug?
To construct the spaceship, whenever you move a spaceship module to the capital, you need to choose the option to "add" it to the spaceship. The module will disappear and your spaceship will receive it (if it's the first module you add, a 3D model of a spaceship will also appear near the city). This option should be listed at the command bar on the left, just like other unit options.
However, you cannot add modules to the spaceship if one of these applies:
As you can see, the 3rd case above applies to you. I'm afraid you cannot conquer the stars in this game... you have no choice but to start another :) enjoy your all-nighter!