I've been saturated in fantasy gaming for most of this year now (and last year, too!) and I am getting the Scifi itch again. The question is....what system?
Traveller remains a viable and well supported system and the Imperium is a perfectly good, venerable setting. Arguably Traveller is SF gaming's standard candle of excellence.
I happen to really have an interest in The Stars are Fire, which is the SF expansion for Cypher System. I had developed and run a couple one-shots in a future setting where humankind lost Earth long ago (for various reasons), and the distant colonies of this future, once more restored to starfaring powers, stumble across the relics of what mankind's old empire had grown in to before it collapsed. Running this would be a breeze with The Stars are Fire, which is full of useful stuff for SF gaming.
I also have Mothership, which is a curious breed apart. It's core book is a zine game, essentially, with densely packed rules for rolling up space truckers and laborers (it's not shy about its influence coming from Alien, Outland and Dead Space). The meat is in the swathe of supplements which are mostly all in a similar format, with a heavy emphasis on exotic artistically eccentric approaches to outlining a variety of settings in which your space truckers might get eaten, absorbed, mutated or mind controlled. The biggest obstacle I can see if that it's a lot like Call of Cthulhu on overdrive: you can play Call of Cthulhu as a campaign for a long time as long as the GM (and players) are mindful of how often nightmarish situations arise to slaughter or drive everyone mad. In Mothership, each setting seems dedicated to topping off the level of doom and destruction from the last, and some are completely over the top. The digital editions of some of the scenarios even include voice recordings and other fun things. All told, though, Mothership does feel like it works best for one-shots and short campaigns. I may test that theory soon.
There is also Esper Genesis, but I am still holding out for their version of the DMG, the Operations Manual, which is about a year or two past due right now. I've also ruled out M-Space for various reasons, mostly because the underlying design assumptions in M-Space just don't quite align with what I want out of a game.
Anyway.....still thinking it over. Been re-reading a lot of Larry Niven lately, and also catching up on Neal Asher, so lots of inspirational ideas! I've always been a fan of Known Space, and Asher's Polity is quite interesting.