NASA concept for a long-duration exploration vehicle capable of travel to Mars and beyond. Nautilus-X would be assembled near Earth, tested by journeying to lunar orbit, and be reused for different missions. A centrifuge is included to help the crew cope with microgravity, though the wheel doesn't seem to have much headroom. This design isn't as simple and sexy as 2001's Discovery, and would have serious problems with crew radiation exposure. Still it is nice to see someone in the office thinking this far ahead.