This repair mission installed two entirely new instruments, repair two inactive ones, and replace a few parts, all completed over the course of five six-and-a-half hour spacewalks. An overview:
Replacements included new gyroscopes, which are used to orient the space telescope to aim it at new starscapes, and new batteries, which are used to store energy during the “nighttime” portion of Hubble's orbit in the shadow of the Earth. New insulating blankets have also been added to help protect the delicate equipment, and the old ones brought back for analysis of how to make future insulating blankets all the better.
New instruments include the Wide Field Camera 3 (WFC3), which will help shed light in dark matter and energy and, being more powerful, replace the WFC2 after one last picture. Also new is the Cosmic Origins Spectrograph (CIS), which will increase Hubble's sensitivity in the ultraviolet spectrum.
But how are all these new things fitting in? A new state-of-the-art circuitry was introduced, the Application-Specific Integrated Circuit, or ACIS, which reduces the size of much of the circuitry inside the Hubble telescope. This allows for more room for all those cool new gadgets.
Repairs include that of the Advanced Camera For Surveys (ACS), specializing in single sources of light, and the Space Telescope Imaging Spectrograph (STUS), which specializes in larger starscapes.
Some of these repairs proved to be a little difficult at times for the astronauts, as thoroughly trained as they were: Hubble's 19 years in space had led to stuck bolts and misfit parts. However, all such obstacles were successfully hurdled: despite the difficulty of the mission, all the repairs, replacements and additions to the Hubble telescope in the end went quite smoothly.
Hopefully, this will lengthen Hubble's lifespan until at least 2014. After that, no more repair missions are currently planned: this repair mission was officially referred to as the “fifth and final” repair mission to Hubble. The planned replacement telescope, the James Webb Space Telescope, is currently scheduled for launch in 2014. However, one of the additions to the space telescope was a docking ring—just in case NASA changes its mind.