Doug, Ross and Don just got done explaining that to me on the Errata thread.
From what I gather, Starship Officer Elite professions can be acquired by non-Starship Officers if they have all of the prerequisite skills (I'm assume that doesn't include the Starship Duty prereq, since you can only get that through the SSO profession, even though it is included in the list of prerequisites).
For SSO's, who get the "Starship Duty" ability when they choose that profession, are automatically able to choose one Starship Officer Elite Profession (waiving all of the prerequisite skills). SSO's can take the Starship Duty ability again (with advancements), allowing them to choose a second elite profession, and so on, with the stipulation that a character can only "advance" in two professions at the same time (their words).
Davy Jones
"Frightened? My dear, you are looking at a man who has laughed in the face of death, sneered at doom, and chuckled at catastrophe! I was petrified."
-- The Wizard of Oz