In addition to what the others have said, in real life, international space law was based on maritime law. They even based directions on maritime law as the sailors used the stars to navigate, and that’s all you have in space to navigate with. So rockets and spacecraft call their directions the same as ships and sailing vessels, they have a port and starboard side, a bow and stern, up is zenith, down is nadir.

Fun fact the actual directions have some cool historical meanings. Nadir is the lowest point in elevation in the surrounding area, aka the bottom of the boat, and zenith is the area directly above you. So you could measure your latitude by measuring a star’s position relative to your zenith. Port was the side you docked on, because your steering oar was on your right. Starboard is a bastardization of the word stéorbord which is what the steering oar was called.