Not sure how they would fit but....aliens...

[Akoree]

not if they are stuck in a planet that doesn't move.

and said swords have no form of propulsion. An engine generates power, the things attached to it cause the acceleration.

To close this side of the discussion, the Ragnarok is a spaceship as stated in the duty finder description:

At the depth of 1233 yalms, your party comes upon the fragment of Dalamud the Garleans had sought. Its true identity is the Ragnarok, a collossal starship which fell away from the less moon moments before Bhamut burst free of his prison...