Wouldn a robotic mission to service Hubble be even more expensive than sending astronauts?
No. Depending on what one includes in the calculation (actual costs, or including the fraction of initial investment, etc.) a single Space Shuttle launch costs up to 1000 million US Dollars. Even developing a robotic mission from scratch would cost less than that. In addition, some limited robotic capability is required in any case in order to bring Hubble down in a controlled manner: Several of the heavy elements of the telescope, like the main mirror, will survive re-entry, and they might cause damage on the ground. So it is important to de-orbit the telescope in such a way that it lands in the Pacific Ocean (or lift it into a much higher orbit).
