Originally scheduled for launch in June of 2000. Hubble’s third servicing mission was
going to upgrade and refurbish the telescope, just as the first two servicing missions had
done.
But in quick succession, Hubble’s all-important gyroscopes began to fail… A Hubble emergency
was declared, and Servicing Mission 3 was split in two.
SM3A’s main priority would be switching out all the gyroscopes with new and improved
versions, while SM3B was scheduled for a few years later and would work on the updates
that Hubble still needed, but weren’t as urgent.
The 8-day mission had 3 spacewalks planned; the first was the gyro replacement, and by
the end of the day Hubble’s gyro troubles were over.
The next two days had their own spacewalks: updating Hubble with a more advanced computer,
adding a new fine guidance sensor, installing a new solid-state digital recorder, and replacing
the outer insulation in order to protect Hubble’s scientific equipment.
When all the work was finished, Hubble was released back into orbit on Christmas day,
and as the crew of Discovery landed at Kennedy Space Center, it became clear that this mission
was a resounding success. Allowing Hubble to continue forward with its mission of uncovering
the mysteries of the universe.