WEBVTT FILE 1 00:00:05.606 --> 00:00:11.345 >> The Hubble Space Telescope has had five servicing missions Since its launch in 1990, 2 00:00:11.345 --> 00:00:17.518 >> from Servicing Mission 1 in 1993 to Servicing Mission 4 in 2009. 3 00:00:17.518 --> 00:00:23.790 >> Wait, what? Five servicing missions but the last one is called Servicing Mission 4? 4 00:00:23.790 --> 00:00:27.527 >> While it might seem strange at first, there’s a reason for that, 5 00:00:27.527 --> 00:00:31.498 >> and that’s because Servicing Mission 3 has a very interesting history. 6 00:00:31.498 --> 00:00:36.970 >> Originally scheduled for launch in mid-2000, Hubble’s third servicing mission was 7 00:00:36.970 --> 00:00:39.473 >> going to upgrade and refurbish the telescope 8 00:00:39.473 --> 00:00:42.809 >> just as the first two servicing missions had done before. 9 00:00:42.809 --> 00:00:48.749 >> But in quick succession, Hubble’s all-important gyroscopes began to fail. 10 00:00:48.749 --> 00:00:52.653 >> So, why are Hubble’s gyroscopes so important? 11 00:00:52.653 --> 00:00:56.356 >> Hubble deputy project manager Jim Jeletic can explain. 12 00:00:56.356 --> 00:00:59.626 >> So, while we're turning Hubble we need to know exactly 13 00:00:59.626 --> 00:01:03.530 >> which direction we're turning it. So we use a sensor known as a gyroscope, 14 00:01:03.530 --> 00:01:09.069 >> or a gyro. They use the conservation of angular momentum to tell us 15 00:01:09.069 --> 00:01:12.572 >> if Hubble is turning in which specific direction, 16 00:01:12.572 --> 00:01:15.242 >> and how fast it's turning in that direction. 17 00:01:15.242 --> 00:01:20.213 >> So essentially without the gyroscopes, we have no way to know where Hubble is pointing. 18 00:01:20.213 --> 00:01:23.417 >> Which, for a telescope, is kind of important. 19 00:01:23.417 --> 00:01:28.522 >> In 1999, Hubble needed at least three of its six gyroscopes 20 00:01:28.522 --> 00:01:30.857 >> to be running in order to do science, 21 00:01:30.857 --> 00:01:34.728 >> and with only three gyros still functioning, a Hubble emergency was 22 00:01:34.728 --> 00:01:41.435 >> declared and Servicing Mission 3 was quickly split into two separate launches. 23 00:01:41.435 --> 00:01:45.639 >> SM3A’s main priority would be switching out all the gyroscopes 24 00:01:45.639 --> 00:01:49.309 >> with new and improved versions, while SM3B 25 00:01:49.309 --> 00:01:52.679 >> was scheduled for a few years later and would work on the updates 26 00:01:52.679 --> 00:01:55.983 >> that Hubble still needed, but weren’t as urgent. 27 00:01:55.983 --> 00:02:00.320 >> Due to this timing change, the astronauts for SM3A had less time 28 00:02:00.320 --> 00:02:04.191 >> to train for their important mission, but they went into overdrive 29 00:02:04.191 --> 00:02:09.730 >> and were ready in time for their launch date of Oct. 14, 1999. 30 00:02:09.730 --> 00:02:14.835 >> However, delays caused by final inspections and wiring repairs on the shuttle 31 00:02:14.835 --> 00:02:19.139 >> continued to push the launch date deeper into the end of the year. 32 00:02:19.139 --> 00:02:22.909 >> And then, as if things couldn’t get any worse, in mid-November, 33 00:02:22.909 --> 00:02:27.547 >> a fourth gyroscope on Hubble failed. Hubble was put into safe mode, 34 00:02:27.547 --> 00:02:30.751 >> and all science came to a screeching halt. 35 00:02:30.751 --> 00:02:35.288 >> Thankfully, the Hubble team had decided to split SM3 into two missions 36 00:02:35.288 --> 00:02:39.526 >> months earlier, otherwise Hubble would have been totally silent until the 37 00:02:39.526 --> 00:02:42.462 >> originally planned mid-2000 mission. 38 00:02:42.462 --> 00:02:46.400 >> So after a few more delays due to more inspections, rewiring, 39 00:02:46.400 --> 00:02:50.237 >> engine replacements, and bad weather, the crew of SM3A, 40 00:02:50.237 --> 00:02:55.242 >> sitting in the cockpit of the Space Shuttle Discovery, was ready to launch. 41 00:02:55.242 --> 00:02:58.745 >> The 8-day mission had 3 spacewalks planned, the first was 42 00:02:58.745 --> 00:03:02.449 >> the all-important gyro switch-out. There were a few minor problems 43 00:03:02.449 --> 00:03:06.286 >> that came up during the 8-hour. 15-minute-long spacewalk, 44 00:03:06.286 --> 00:03:11.091 >> but by the end of the day Hubble’s gyro troubles were over. 45 00:03:11.091 --> 00:03:14.761 >> The next two days had their own spacewalks, updating Hubble with 46 00:03:14.761 --> 00:03:18.632 >> a more advanced computer, adding a new fine guidance sensor, 47 00:03:18.632 --> 00:03:22.269 >> installing a new solid-state digital recorder, and replacing 48 00:03:22.269 --> 00:03:26.006 >> Hubble's old outer insulation with new panels in order to protect 49 00:03:26.006 --> 00:03:30.777 >> Hubble’s scientific equipment from getting too hot or too cold. 50 00:03:30.777 --> 00:03:34.247 >> When all the work was finished, Hubble was released back into orbit 51 00:03:34.247 --> 00:03:38.618 >> on Christmas day, and as the crew of Discovery landed at Kennedy Space Center, 52 00:03:38.618 --> 00:03:43.123 >> it became clear that this mission was a resounding success. 53 00:03:43.123 --> 00:03:48.528 >> Servicing Mission 3B would also be a success later in March of 2002, 54 00:03:48.528 --> 00:03:55.936 >> followed by the fifth and final flight, Servicing Mission 4 in May of 2009. 55 00:03:55.936 --> 00:03:59.139 >> Thanks to everyone involved with servicing mission 3A, 56 00:03:59.139 --> 00:04:03.777 >> Hubble was able to quickly get back on schedule with its ground-breaking science, 57 00:04:03.777 --> 00:04:14.988 >> and continue forward with its mission of uncovering the mysteries of the universe. 58 00:04:14.988 --> 00:04:18.725 >> So I'm sure you know who I am! You know today is the busiest day of 59 00:04:18.725 --> 00:04:23.497 >> the year for me, I'm delivering presents to good little girls and boys 60 00:04:23.497 --> 00:04:26.500 >> I heard the Discovery was up in space working over the holidays 61 00:04:26.500 --> 00:04:30.203 >> so I decided to stop by and visit my astronaut friends 62 00:04:30.203 --> 00:04:34.508 >> and deliver presents, because they've been good girls and boys! 63 00:04:34.508 --> 00:04:39.246 >> It's a very busy time of the year, so I must be on my way! 64 00:04:39.246 --> 00:04:43.083 >> But I would like to wish all the boys and girls around the world 65 00:04:43.083 --> 00:04:47.187 >> a Merry Christmas! Especially those ones down in Houston 66 00:04:47.187 --> 00:04:50.357 >> in Mission Control at the Kennedy Space Center who have done so much 67 00:04:50.357 --> 00:04:54.194 >> work during the holidays to make this mission such a great success! 68 00:04:54.194 --> 00:04:58.331 >> It's a busy, busy year so I've gotta go! Merry Christmas boys and girls! 69 00:04:58.331 --> 00:05:07.140 >> Merry Christmas!