The Hubble Space Telescope would not be able to produce its breathtaking science without the upgraded infrastructure targeted during the HST SM4 mission: Fine Guidance Sensor, Scientific Instrument Command and Data Handling, Soft Capture Mechanism, Batteries, and New Outer Blanket Layers. Along with all new cameras, scientific instruments, the Hubble telescope will work better than it ever has in its lifetime.
Wide-Field Planetary Camera 2 (WFPC2) was installed in Dec 1993 and used to obtain high resolution images of astronomical objects. This camera was removed in the last servicing mission so it is no longer in service.