Go to the single player folder (c:\Program Files\Taldren Software Inc\Starfleet Command Orion Pirates\MetaAssets\ServerProfiles\Singleplayer), and hit ctrl-a to select all. Then right-click the selected documents, and click 'properties'. Archive will list in there.
Also, for note, a lot would say the 'better' route (since single player missions are incompatible between patches), is to uninstall OP, then reinstall it and use the 2500-2538 patch.