Superconductors can be made to levitate in a magnetic field. They try to expel magnetic fields from within themselves, a very unique property. In space, it would be easy to keep material at temperatures close to absolute zero, meaning that a system using this could conceivably be propelled without any energy at all, at least in regions of space where there are magnetic fields. Here is a link to the talk: http://www.youtube.com/watch?v=4HHJv8lPERQ
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