NX

NX has been a prefix for Federation starship registry numbers since its inception in the late 22nd century, derived from the NCC prefix of the Federation Starfleet.

"NX" stands for "Naval, eXpermimental", and can refer to any vessel that contains entirely new technologies and/or design concepts (such as the four-nacelle USS Constellation NX-1974), or merely the first starship of a particular class (such as the new-design USS Excelsior NX-2000), before it is approved for class production.