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Originally scheduled for launch in June of
2000, Hubble’s third servicing mission was

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going to upgrade and refurbish the telescope,

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just as the first two servicing missions had done.

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But in quick succession, Hubble’s all-important
gyroscopes began to fail… A Hubble emergency

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was declared, and Servicing Mission 3 was
split in two.

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SM3A’s main priority would be switching
out all the gyroscopes with new and improved

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versions, while SM3B was scheduled for a few
years later and would work on the updates

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that Hubble still needed, but weren’t as
urgent.

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The 8-day mission had 3 spacewalks planned;
the first was the gyro replacement, and by

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the end of the day Hubble’s gyro troubles
were over.

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The next two days had their own spacewalks:
updating Hubble with a more advanced computer,

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adding a new fine guidance sensor, installing
a new solid-state digital recorder, and replacing

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the outer insulation in order to protect Hubble’s
scientific equipment.

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When all the work was finished, Hubble was
released back into orbit on Christmas day,

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and as the crew of Discovery landed at Kennedy
Space Center, it became clear that this mission

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was a resounding success.