E.g. The Voyager crafts took various assists from the planets. Sun being much more massive, wouldn't a spacecraft gain much more energy from such a flyby on the correct trajectory? If so then what fraction of $c$ could we achieve?

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    $\begingroup$ Voting to close, sorry, this is a duplicate of physics.stackexchange.com/q/128356 also related to physics.stackexchange.com/q/134473 $\endgroup$ – user81619 Nov 3 '15 at 13:38
  • $\begingroup$ @count_to_10 I agree. Shall I delete this? $\endgroup$ – iceman Nov 3 '15 at 13:43
  • $\begingroup$ Sorry about that, been there myself, imo yes, but it takes 5 votes so it's up to you. $\endgroup$ – user81619 Nov 3 '15 at 13:44