I agree with Parravon about FA having no triggers. But i think thats just why it cannot be used twice a turn. Let me explain, the better i can, since english is not my mother language:
FA is an ability you choose to use. It has no triggers, since it has no "when something happens" clause in its text (i dont want this to be a "whats a trigger" discussion. As i said, i agree with Parravon in this, he explained it very well, so go read his post if i have not been clear enough). As it has no triggers, there's nothing simoultaneous between the two copies of FA: one is chosen to resolve first, then the other.
When you want to resolve anything in this game, you have to check if you meet the requirements to do so. The requirement of resolving FA is, as far as i know, being able to perform an attack (and having at least 1 hull left, but that's not the topic here). That's why you cannot use it when you are overlaping an asteroid, or when you have a Disabled Munition token (you see, most times the FAQ clarifications are for a reason, not just a "because i say so" thing). Its simple: if you are able to attack, you can use FA instead. If you are not, you cannot.
So, at this point i think all of you know where i want to go. The sequence will be something like this:
-i have two copies of FA. Want to use them
-i choose one.
-i check if i can resolve FA. i'm able to attack because i have nothing that doesnt let me to. Im not overlapping a rock, i have no stupid Disabled Munition tokens. Who cares about having a valid target? Im not talking about that. Okay, i need one enemy to be at range 1. I meassure that (since i am trying to resolve an ability that requires a certain range, im allowed to do so).
-i pay FA cost: take 1 damage, take 1 ion token.
-i resolve FA ability: my enemy takes 1 damage.
-FA consequences (not cost) come to play: i cant attack anymore in this round.
-i choose the other FA.
-i check if i can resolve the second FA. Theres a game effect that doesnt allow me to attack. I cannot resolve FA, as if i were standing on a rock.
I hope i at least made my point clear.