Hm. How much of these needed space shuttle modifications are there already realised, or in progress, or planned at all? Do we have effective shield technology at hand? And by effective I think it should at least have been half an our in let's say Mercury's orbit to be of any use.
Or, do we have tested and established small space craft nuclear reactors? How much of the needed "hardware" for a space craft that is actually useful for use together with a hyperdrive-engine is already developed tested and waiting for action?