Fly as a capital ship
There is a trick that FREDers can do while FREDing a missiion that can allow them to pilot ships that they normally can't. This includes freighters, cruisers, capital ships, and even the Colossus.
For starters, suppose that you have 2 ships on a custom map. Alpha 1 is in a Loki, while Beta 1 happens to be an Orion. Save the game, start Freespace 2, go to mission simulator, and select this mission. When your there, go to ship selection and there will be 2 icons, Alpha 1 (you) is a loki, and Beta 1 is an Orion. Switch those 2 ships and start the mission. Congratulations, your flying an Orion now.
Issues: OMG, this thing is soooo slow---- Well, capitial ships arn't really speedy, but you can switch power to the engines and the ship should go much faster. I reached 60mph in a Deimos corvette.