I think not saying exactly when it is set is actually a good move, and so is keeping the back story of what's happening on Earth vague. You avoid appearing dated in a few year's time (like all the sci-fi movies/shows where the Soviet Union exists beyond 1989) and it allows you to add details to the backstory later on if you desire (ok, given the not so great viewing figures, this is probably a moot point).
But even if they did shout from the rooftops that it's 2040, it wouldn't bug me that much. Then again, I'm somewhat desensitised in that regard due to Doctor Who with its extensive (British) space flight program in the 1970s among other things. So far, the story's still gripping me.