The second servicing mission was in February, 1997.
After the space shuttle crew captured the observatory in orbit and berthed it in the Shuttle cargo bay, four astronauts worked in pairs on alternating days, doing four days of spacewalks to replace instruments and installing other critical components.
The primary objective was to replace the Goddard High Resolution Spectrograph and the Faint Object Spectrograph with two dramatically improved instruments: the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) and the Space Telescope Imaging Spectrograph (STIS).
Astronauts also replaced a Fine Guidance Sensor needed to point the telescope at celestial objects; a tape recorder used to record data; an electronics package that drives the telescope’s solar arrays; and a communications unit that translates ground-based commands and relays the information to onboard instruments and systems. In addition, astronauts installed a new solid-state data recorder, which is important because the two new science instruments gather enormous quantities of data.
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