Superman's Rocket was built by his father, Jor-El, and used to send baby Kal-El to Earth to live his life there and carry on their planet's legacy as "The Last Son of Krypton." It was later modified by Dr. Emil Hamilton and the scientists at S.T.A.R. Labs to allow Superman to explore space when his space suit would not be enough on its own. Where Superman kept it is unknown, though it was likely in his Fortress of Solitude.