re: only the SHUTTLE can save Hubble
Can those rockets take enough trained astronauts, their spacesuits, grab the HST, carry the equipment (gyroscopes, new mirrors, etc), go all the way up to 600 km height and spend a week up there (4 or 5 successive spacewalks)?
If some of those requirements (normally met by the shuttle) cannot be satisfied, then it might not be worth it.(Why go back to the HST only with a new instrument and no gyros or only with gyros and no new equipment?).
Raoul