The New GURPS Space has excellent advice on SF settings and campaigns, including lengthy chapters on building or rolling up star systems and alien creatures/races. It doesn't have any equipment, though - but the new GURPS Ultra-Tech has lots of that.
Spaceship construction rules for GURPS 4E are still in playtest, as far as I am aware - but you could use those from GURPS Traveller: Interstellar Wars instead, which is set in an earlier period of the Traveller Universe where the Terrans first set out to explore the stars - and in the process take on the Vilani Empire with its thousands of worlds and vastly older civilization.
Beyond GURPS, there is Blue Planet - a campaign setting taking place on a newly settled water world that can be reached from the solar system via a wormhole. It's fairly hard SF and set in the not too distant future, but its description of the alien environment and the politics of the colony are top-notch. Since the game is out of print, I suggest you try to get any books from the line you can find - they are all worth it.
You already know Transhuman Space. But you should really get all the sourcebooks as well, especially "Toxic Memes" which I wrote for.

A PDF supplement named "Changing Times" for this game is available which both updates it to GURPS 4th Edition and serves as a GMing guide.
Then there are Heavy Gear and Jovian Chronicles. The latter is set in a throughly settled solar system and a bit similar to Mobile Suit Gundam, complete with giant robots. It is very well developed and a lot of fun. The former is set a few thousand years in the future. It starts on a remote former colony of Earth which is close to a war between its major nations, but its storyline soon evolves into an interstellar drama. I wish they'd produce more material for it, but the amount of stuff they've published is already rather large. Both of these settings use the "Silhouette" rules system, which is quick and simple, though the latest editions of the settings books also have d20 stats.