Merits of 1st In vs Space 4e?

[Jon F. Zeigler]

There's a natural progression in place:

1. Classic Traveller, Book 6 (Scouts)
2. GURPS Traveller: First In
3. GURPS Space 4/e

The system in First In was based on the old Book 6 system, with a lot of research done to correct errors and make the system more flexible. It gives perfectly good results but in some ways it's not as useful as it could be - for one thing, it's not obvious how to run the system backwards so that you start from a planet of desired properties and work your way to the rest of the star system. You'll end up with a lot of red dwarf stars with no habitable planets . . . The system isn't tied to the old Traveller hexadecimal strings, nor does it use metric, although it's easy enough to translate if you want to.

The Space 4/e system is a further development of the same idea, with still more research behind it. There's more real-world astrophysics built into the process, although I tried to make that as transparent as possible. This version is pretty generic, not tied to Traveller at all except very indirectly. It doesn't use metric either. It's a fairly flexible tool-kit; this is the one I'd recommend you pick up.

The world-design rules in GURPS Traveller: Interstellar Wars could be considered a subset of the GURPS Space 4/e system, tailored for a Traveller-like setting and with a lot of the flexibility taken out in favor of ease of use.

There are certainly further improvements that could be made to the Space 4/e system. I used some weird units in an effort to make the math as transparent as possible - if I had it to do over again (and if I wasn't writing for GURPS) I'd probably use metric instead. Meanwhile, Brett Evil has done a lot of work to make pieces of the system more scientifically rigorous - his treatment of tidal braking, for example, is math-heavy but much better than what's in the book.