School me, why can't they use the current fleet of Shuttles to go to the moon?
If not indefinitely, then how about a last ditch effort for them, put the required moon vehicles and whatnot in them, and LAND the shuttles on the moon with no plans for sending them back. They could be used to chain together the first moon base or something.
Escape velocity from Earth is >27k mph. The Shuttles barely break 18k mph, in low Earth orbit. They simply don't have the delta-v (booster power) to truely break Earth's gravitational pull and get all the way to the moon, and aren't designed for any fancy maneuvers like gravitational slingshots. There's no real way they could ever reach trans-lunar injection orbit.
If you consider the size of the Saturn V (huge!) that went to the Moonand the size of the command module (tiny!) versus the size of the Shuttle's tank and rocketry (medium sized) and the Shuttle itself and its payload (medium sized) you begin to get a sense of the problem.
The highest Earth orbit ever reached by the Shuttle is less than 400 miles.
To put this in to perspective, a geostationary satellite used to beam TV to peoples' homes orbits in the Clarke belt at an approximate height above Earth of 22,000 miles (although they don't typically reach this altitude directly, they do so via geostationary transfer orbit).
The Moon is 240,000 miles away. Ouch.
This is just a guess also, but I'm not sure the shuttles have sufficient radiational shielding to ensure the safety of the occupants where the Earth's magnetosphere is much weaker.
One hypothetical scenario that would be more feasible would involve refuelling a larger Moon-bound craft in Earth orbit, but setting up the infrastructure for space refuelling alone would cost billions of dollars more than NASA has for the remains of the shuttle programme.