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Well... if you're going to offer me the chance to be picky about typography....
The size of the bars from the galaxy logo usually should be the same weight as the width of the font (since it's a sans font and everything is pretty consistent), however, they feel much too light since they don't visually occupy the same space as an N/M that surround them (closer to the visual area of the L), thus you need them to be a wee bit heavier, like in the first. Additionally, the thin options feel too thin, like they're getting away from the Galaxy logo.
Absolutely use the astronomical-O from the third.
I'd actually +1 two graphical elements in the logo, as it is 100% associated with Galaxy and should make that obvious. The O is just a nice bit of flair that would make it otherwise be a bit dull "hey we stuck a galaxy logo in our typography"