What will replace the Space Shuttle?
I think it has served it's purpose and should be retired. In the near future, I think a space capsule, like an enlarge Apollo, who do the trick. How hard would it be to launch it on a Titan 4? If you can seat 5-6 Astronauts it would be great, but it would be wasteful to use it for fixing orbital satellites and the like. How difficult would it be to replace the Saturn booster series?
What the U.S. lacks at the moment is a very heavy lift booster. - All the eggs where put in the Space Shuttle basket. Here is a vehicle that is older than I am, by a good bit!! LOL