This topic was discussed awhile back, if I remember correctlysomeone posed the question of making a ship that can only use afterburners. I'm not sure if a solution was ever reached, but I think that this might have worked:
- Make an invisible, damageless weapon with a negative recoil called "Engines". Set it to be a secondary weapon and to drain fuel.
- Also create a ship with no acceleration and relatively low mass.
- When the ship fires this secondary weapon, it will move forward.
This will have the side effect of giving the player infinite top speed, and I doubt the AI could use it properly, but I'm pretty sure it could work.