Before computer graphics were viable, the props for Star Wars were developed using models.  The styrene globe that Colin had ordered for the Death Star model arrived in 2 halves. Unfortunately, the edges of each half had shrunk slightly so that the two halves had a very tiny dip around the circumference. From his experience, Colin knew that it would take hours of work to connect the two globe halves so perfectly that a line would not show around the middle when the model was lit from the side with studio lights. With this in mind, Colin called George Lucas and asked him what he thought about the idea of creating a trench around the center of the Death Star. Colin sold the idea to Lucas by explaining that the Death Star could have armament projecting from the sides of the trench resulting in spectacular battles with starships flying in and out of the trench. George said to Colin that he needed to think about it. So, when George called back and agreed to the trench, Colin’s extra work was avoided and the Death Star got its trench.