The cylindrical hull of the Discovery was made up of the first and second stages of the Saturn V kit. Half circle openings were cut in the ends of the two stages where they joined to accept the spokes of the "habitation ring." Again, it was lucky that the first stage is about twice the length of the second stage so this placed the habitation ring about a third of its length back from the bow, which is just where it should be to replicate the cover artwork.