Unpacking Starbound assets - Pfhoenix/Starbound-Mass-Effect-Edition GitHub Wiki
Just as a reminder, original post is found here: http://community.playstarbound.com/index.php?threads/how-to-successfully-pack-and-unpack-pak-files.66649/
Short version (for Windows):
Goto to your Starbound binary folder, e.g. "C:\Program Files (x86)\Steam\SteamApps\common\Starbound\win32". Open commandline as administrator and type in:
asset_unpacker.exe ..\assets\packed.pak ..\assets\unpacked
Important: The path to where you extract it (unpacked) to MUST point to a non existing folder or it'll error out on you.