After Shuttle is: The Next Generation - Project Orion
(http://bruce.org.uk/images/orioncraft.jpg)
Shuttle was retired during 2011 but this did not mark the end of NASA's manned space exploration ambitions. Their skunkworks were already developing the next generation.
And to date they have achieved a lot as you can see in the illustration above.
Below is the reality of the above concept.
(http://bruce.org.uk/images/orion.jpg)