>> The Hubble Space Telescope has had five servicing missions Since its launch in 1990,
>> from Servicing Mission 1 in 1993 to Servicing Mission 4 in 2009.
>> Wait, what? Five servicing missions but the last one is called Servicing Mission 4?
>> While it might seem strange at first, there’s a reason for that,
>> and that’s because Servicing Mission 3 has a very interesting history.
>> Originally scheduled for launch in mid-2000, Hubble’s third servicing mission was
>> going to upgrade and refurbish the telescope
>> just as the first two servicing missions had done before.
>> But in quick succession, Hubble’s all-important gyroscopes began to fail.
>> So, why are Hubble’s gyroscopes so important?
>> Hubble deputy project manager Jim Jeletic can explain.
>> So, while we're turning Hubble we need to know exactly
>> which direction we're turning it. So we use a sensor known as a gyroscope,
>> or a gyro. They use the conservation of angular momentum to tell us
>> if Hubble is turning in which specific direction,
>> and how fast it's turning in that direction.
>> So essentially without the gyroscopes, we have no way to know where Hubble is pointing.
>> Which, for a telescope, is kind of important.
>> In 1999, Hubble needed at least three of its six gyroscopes
>> to be running in order to do science,
>> and with only three gyros still functioning, a Hubble emergency was
>> declared and Servicing Mission 3 was quickly split into two separate launches.
>> 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.
>> Due to this timing change, the astronauts for SM3A had less time
>> to train for their important mission, but they went into overdrive
>> and were ready in time for their launch date of Oct. 14, 1999.
>> However, delays caused by final inspections and wiring repairs on the shuttle
>> continued to push the launch date deeper into the end of the year.
>> And then, as if things couldn’t get any worse, in mid-November,
>> a fourth gyroscope on Hubble failed. Hubble was put into safe mode,
>> and all science came to a screeching halt.
>> Thankfully, the Hubble team had decided to split SM3 into two missions
>> months earlier, otherwise Hubble would have been totally silent until the
>> originally planned mid-2000 mission.
>> So after a few more delays due to more inspections, rewiring,
>> engine replacements, and bad weather, the crew of SM3A,
>> sitting in the cockpit of the Space Shuttle Discovery, was ready to launch.
>> The 8-day mission had 3 spacewalks planned, the first was
>> the all-important gyro switch-out. There were a few minor problems
>> that came up during the 8-hour. 15-minute-long spacewalk,
>> but 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
>> Hubble's old outer insulation with new panels in order to protect
>> Hubble’s scientific equipment from getting too hot or too cold.
>> 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.
>> Servicing Mission 3B would also be a success later in March of 2002,
>> followed by the fifth and final flight, Servicing Mission 4 in May of 2009.
>> Thanks to everyone involved with servicing mission 3A,
>> Hubble was able to quickly get back on schedule with its ground-breaking science,
>> and continue forward with its mission of uncovering the mysteries of the universe.
>> So I'm sure you know who I am! You know today is the busiest day of
>> the year for me, I'm delivering presents to good little girls and boys
>> I heard the Discovery was up in space working over the holidays
>> so I decided to stop by and visit my astronaut friends
>> and deliver presents, because they've been good girls and boys!
>> It's a very busy time of the year, so I must be on my way!
>> But I would like to wish all the boys and girls around the world
>> a Merry Christmas! Especially those ones down in Houston
>> in Mission Control at the Kennedy Space Center who have done so much
>> work during the holidays to make this mission such a great success!
>> It's a busy, busy year so I've gotta go! Merry Christmas boys and girls!
>> Merry Christmas!