Nautilus-X (Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration) is a rotating wheel space station concept developed by engineers Mark Holderman and Edward Henderson of the Technology Applications Assessment Team of NASA.

To ease route planning of the whole mission, the station would be placed at the Lagrange point L1 or L2 of the Moon or Mars, depending on which location is to be visited.

The design was modular, enabling it to accommodate any of a number of mission specific propulsion modules, manipulator arms, docking port for an Orion or commercial crew capsule, and landing craft for destination worlds.

The Extended Duration Explorer variant on the Nautilus-X design concept would have several more, plus docking bays for science payloads and away-mission vehicles.

In order to deploy this massive spacecraft as easily as possible, it would consist of a variety of rigid and inflatable modules and solar dynamic arrays.