Exactly. That thing is not a typical juggernaut, it's some sort of hangar or anchor. The juggernaut from Prometheus is the same make and model as the derelict from Alien. We can all gnatf**k over concept art from 1978 if we really want to but it's not going to make a difference in 2017. Derelict=juggernaut/Engineer=space jockey, and David's about to kill them all. Move on with ya lives.