Arion Games have published Stellar Adventures. I've yet to read it all, as yet, but it'll very likely be my go-to game for all kinds of science fiction adventuring, as Advanced Fighting Fantasy has come to dominate my fantasy gaming.
Here, I've printed the chapters out in handy digest form. I also found a few source books!
That said, I could imagine myself using some of the sandbox creation tools in the brilliant Stars Without Number (as well as the GM guidance in that book, and its supplements), and would probably struggle to avoid drawing heavily on the original Rogue Trader - I picked up the reprint from Warhammer World a few weeks ago...
