The shuttle plus payload is around 100 tons in orbit; delta-v to get to lunar orbit is about 4.5 km/s total. With LOX/LH2 at Isp of 455, the mass ratio needed would be about 2.9, requiring 190 tons of propellants not counting tankage and engines.
Since shuttle payloads are max about 25 tons, this would require eight launches just for the propellants- only to deliver 25 tons of usable payload to lunar orbit. It would be far cheaper to develop new vehicles from scratch rather than transport a shuttle to lunar orbit.
If you want to return the shuttle to earth, it gets even uglier.
The best near-term way to get large payloads to the moon would be to use Ariane 5 vehicles to put up a bunch of stages in LEO, dock them together, then drop stages as needed along the way. Cheaper, and little new machinery need be designed.
> Yikes Spike! Certainly not. What I was suggesting is that
> you strap some kind of inter-orbital transfer booster on
> after it has achieved LEO. The delta-V necessary to get to
> LEO is already (4/5?) the amount necessary to get to lunar
> orbit and back. So I'd imagine these inter-orbital boosters
> would not have to be nearly as big or dramatic as the
> solid-rocket boosters used on takeoff.
-- Doug Jones, Freelance Rocket Plumber