Hubble part I
To recap: Hubble Space Telescope was due for another servicing mission, to install two new instruments (WFPC3 and COS), do some upgrades, and, critically, to install new gyros. The old gyros have a very finite life, one will probably be lost in next year or two, the rest within a few more. Two are already gone, so one more lost means switching to a 2-gyro pointing mode with limited pointing range and worse stability. Lose another one, and HST goes into safe-mode, no more observing. Lose the last one it tumbles and burns in uncontrolled re-entry.
Past NASA head cancelled the servicing mission, Shuttle is to go to the Space Station only, based on a moderately convoluted interpretation of the Columbia accident panel recommendation, and an unwillingness to committ to having a second shuttle on the pad for a "rescue launch" (no rescue needed, the other Shuttle goes to Space Station or whatever). Part of the problem, as I understand it, is that NASA switched to a full cost accounting, and the science budget just can't bear the contingency funding for the 2nd shuttle launch. Sounds superficially sensible as an accounting method, is moderately insane in practise.
What is particularly galling, is that federal admin people came to the AAS meeting in San Diego, and without explicitly promising anything, strongly suggested that the HST robotic rescue mission would be in the President's budget. Chipper little OMB official, never promised anything. just suggested. Final budget has a billion to develope the capability and launch a robot to destroy Hubble through controlled re-entry. Not enough for a refurbishment mission.
What a waste.
From a strict monetary view, the case is ambiguous. It'd be comparable cheap to fly a new mission like HOP, with the built instruments. HST is old, except that just about everything but the mirror and frame have been replaced. multiple times in some cases. It was good for another decade with one more refurbishment. And the reality that the rescue/controlled crash funding is new money, there's no way the admin or congress would actually give funding for a new comparable capability telescope before NGST or SNAP fly.
US could be left with no serious optical/near-IR imaging or spectroscopy in orbit for a decade. Oh, and astronomers could be left without a key source of funding for individual and small group projects, but that is for another time (and not as self-serving as it seems, I'm a theorist).