Curvature ships played an important role in Star Trek, without it, Kirk would have a hard time escaping, which directly led to the general engine being left out in the cold. So, does such an engine really exist?
If people will stop trying to kill it, SLS might evolve into Energia II, allowing the shuttle of Figure 21.
Subsonic Lift to Drag ratio improved to 6.02
I might put jets on it for self ferry.