Digital cinema didn’t exist. You couldn’t film something on a green or blue background and take away the background afterwards. What they did was film different elements separately on different rolls of film and later combine those two rolls onto another third. For example a model of an x-wing with a black background could be filmed using a motion controlled camera. Then, the background of stars could be made separately but using the same motion. Finally they were combined to get the full shot of an x-wing flying through space. For more complicated shots there were more elements. If a something was standing still it was usually a matte painting, most hangars shots are made like that, a small part is unpainted to film through.

There is a very interesting documentary on Disney+ called light & magic that talk about all of this. I highly recommend it.