(First off, let me note that Diaspora is normally available only through Lulu.com, but Lulu screwed the pooch recently and the title isn’t currently listed. As soon as it’s back, you want to get yourself a copy. No, it’s not available in PDF yet (and probably not for some time). I may talk more about that publication of Diaspora some other time, but that’s enough about that for now.)
Diaspora is hard science fiction storytelling built on top of Fate. (As it so happens, I know a little about Fate!) At first blush, that’s a weird fit. As a gaming chassis, Fate can give you plenty of detail to work with, but generally it’s all about characters and character-driven stuff. Hard sci fi leaves one thinking that hey, maybe you should instead focus your game system on precise models of physics, concern yourself with resource management in the black depths of space, etc. Which might be true to a limited extent — and that’s the extent to which Diaspora gives it support. Diaspora knows how to grab onto the attitude of hard SF without shouldering its baggage as well. Then it takes a cue from Vernor Vinge (among others) and focuses in on the characters.