I originally was going to put this in the previous post as an update, but it got long enough and covers enough topics to make it its own entry.
The mission update is going on right now as I write this. They will install the two science instruments: the Wide Field Camera 3 and the Cosmic Origins Spectrograph, both of which are sitting in a warehouse waiting to go. They'll replace all six gyros and the batteries. They'll add thermal insulation blankets on the outside of Hubble. They'll replace one Fine Guidance Sensors, an incredible telescope that keeps Hubble locked on to its targets (and which can be used for some science). They'll also install and "over voltage protection device", and a soft capture mechanism on Hubble's aft end to facilitate docking. Finally, they will try to fix STIS, the Space Telescope Imaging Spectrograph, which shorted out a few years ago.
WF3 will replace WFPC2, the Wide Field Planetary Camera 2 installed back in 1993. WF3 is cool-- it uses the original WFPC chassis with all new optics to seriously upgrade the camera capabilities (unlike the current Advanced Camera for Surveys, it has ultraviolet imaging detectors). COS will replace the no-longer needed COSTAR, the optics originally installed to correct Hubble's flawed mirror. Now all on board detectors have optics already installed to correct the flaw.
I'm very excited about the potential repair of STIS. I worked on that camera for many years, and if it's fixed it gives Hubble sight into the far-ultraviolet, which no other camera can do. It will complement ACS, COS, and WF3. However, repairing STIS will be difficult. Taking the cover off the instrument will be the first hard part-- there are 111 screws (yes, one hundred eleven) holding the cover on. Worse, those screws are not designed to be taken out by astronauts! But they have designed a "capture device" to make sure they don't lose any screws. After they get the cover off, they still have to replace the failed electronics board, and that has its own issues. But of course the folks at Ball Aerospace (who built STIS) and at NASA have looked into this as best they can, and they still have time to make sure they understand everything they can about this mission.
This whole mission is going to cost $900 million. A lot of that is already spent, and will be spent over the next 18 months before launch. That includes launch costs, which are significant, of course.
Is it worth it? I think so, but of course there will be detractors. I'll point out, as I always do, that this kind of money sounds like a huge amount when stated baldly, but in fact if you pro-rate it across the timeline and by the people in the US who will pay for it, the cost is actually pretty low considering what we get out of Hubble-- and I don't just mean the science, which is plentiful, but the sheer inspiration of the mission. If you want to make this mission worth it, then go to Google Images, download a good Hubble image, and stick it on your wall. When I hand out Hubble pictures after I give public talks, the kids rush the stage to grab them. The look on their faces makes it clear how worth it Hubble really is.