Space strategy construction set

[montypython]

I've been looking for a space strategy game system that allows for scenario construction a la Star Fleet Battles, Palladium Games or GURPS, for fleet actions such as Zentraedi vs Star Gate or any number of different franchises. Is there any game system out there available for such, or is pen and paper the only way to go?

[Zinegata]

I vaguely recall Space Empires IV being moddable enough to support not only scenarios, but entire new ship sets as well.

[doom3607]

SE:V is harder to put new shipsets into, but that's only because it's in 3D. Other than that, it's probably even more modable than IV.