A game idea just hit me. Having a ship lost in the "Mirror Universe" rather then across the galaxy. With some severe tweaking of the communications systems the ship could contact Star Fleet Command, but the ship would be stuck in a hostile environment for some time. Even if the crew did come up with one of those transporter devices that can send them back, it would still leave the ship there (not something you'd want the Alliance getting their hands on). This could also be used to determine just how dangerous the current mirror governments are to the safety of the normal governments, if SFC decided so.
Personally I wouldn't have a standard Federation ship doing this, I'd go with one of the more combat oriented ships (the 5 First Contact types) just as a point of survival.
Well as I said, this is just a spur of the moment idea that hit me. Let me know what you folks think.
Phoenix...
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"Of all the shadows cast in this world, it is my own that I fear the most"
-Phoenix Merrick 2001