How the big gun works.

Okay, so this is how I think the big space jockey gun/chair gizmo works: First the jockey selects a planet from the big holographic star map and places in that little holder thingy on the floor like it shows him doing in the trailer (He's probably selecting earth here). Then the big gun rises up out of the platform and the jockey sits down in it and as he does so his space suit wraps around his body. Somehow an egg/ampule is lifted up from the room below and loaded into the gun. A hatch on the ceiling opens up and both the jockey and the chair are lifted up through it and out onto the top of the vessel. He targets the planet and the gun launches the egg/ampule to the surface for the extermination of all life on the world. I think the only reason he is wearing the suit at this time is simply to allow him to breathe while outside the ship in the vacuum of space. Their suits are simply space suits. I could be totally wrong though.