Nautilus-X is a multi-mission space exploration vehicle designed by the Technology Applications Assessment Team of NASA.
It would be the first spaceship to travel solely in space, and not return to earth after each mission.
The spacecraft is designed for long duration (up to two years) space journeys for a six-person crew. In order to limit the effects of microgravity on human health, the spacecraft is equipped with a centrifuge.
The spacecraft itself is proposed to be relatively cheap by manned spaceflight standards as it is projected to only cost US$3.7 billion.
In addition, it may only need 64 months of work.
Websites:
http://en.wikipedia.org/wiki/Nautilus-X