VASMIR space tug.
Dock the tug at the ISS when not in use, and it could easily carry it back and forth for maintenance. But since Nasa isn't capable (and/or allowed) of following through on anything, such ideas are a moot point.
We're going to have to wait until the private sector is able to deliver on sending people into space before anything of consequence is done in space by our fallen country. Only then will a space program be resistant to the whims and shortsighted stupidity of D.C.