Editing Hubble Space Telescope (section)

=== Servicing Mission 3A ===
{{Main|STS-103}}

Servicing Mission 3A, flown by ''Discovery'', took place in December 1999, and was a split-off from Servicing Mission{{nbsp}}3 after three of the six onboard gyroscopes had failed. The fourth failed a few weeks before the mission, rendering the telescope incapable of performing scientific observations. The mission replaced all six [[gyroscope]]s, replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets.<ref>{{cite web |url=http://sm3a.gsfc.nasa.gov/overview.html |title=Servicing Mission 3A Overview |publisher=NASA |access-date=April 26, 2008 |archive-date=May 9, 2008 |archive-url=https://web.archive.org/web/20080509190700/http://sm3a.gsfc.nasa.gov/overview.html |url-status=live }}</ref>