class ships will be named after space  shuttles, because this is actually also the order in which the  orbiter fleet was built. Enterprise came first, as a test vehicle  not flown in space, then Columbia. In the order they were produced,  the orbital vehicles (popularly known as spaceshuttles) made after  the first two were Challenger, Discovery, Atlantis, and Endeavour  (built to replace the loss of the Challenger). With NX