This story was updated at 7:43 p.m. EDT.
HOUSTON - A pair of spacewalking astronauts enhanced the Hubble Space Telescope?s sense of direction with some new gyroscopes Friday, but had trouble during the grueling upgrade because of a stubborn part.
Atlantis astronauts Michael Massimino and Michael Good spent nearly eight hours replacing four of the 19-year-old Hubble?s old gyroscopes with new ones - a top priority task - but an electronics box containing the last set refused to fit properly.
?No joy,? Good said when the balky box containing the last two new gyroscopes did not lock in place for the second time. ?It just doesn?t want to fit.?
The spacewalkers were prepared, however, and installed a backup set of refurbished gyroscopes that NASA packed aboard Atlantis just in case. The spare set were an older design with parts rebuilt from earlier units removed from Hubble in 1999, NASA officials said. It will not hamper the telescope?s pointing skills, they added.
The observatory relies on six spinning gyroscopes to maintain its orientation in space and keep its camera eye steady while catching its trademark images of the universe. Three of Hubble?s old gyroscopes have failed over the years and the telescope was running on two, keeping a last one as a spare, until Friday?s successful fix.
?Mass and Bueno, my friend Leonidas has a few words for you guys that are appropriate right now,? said Atlantis commander Scott Altman, using the spacewalkers? nicknames and referring to the Spartan king who died fighting against the Persians in the Battle of Thermopylae in 480 B.C. ?Remember this day men, for it will be yours for all time.?
The gyroscope trouble pushed the astronauts nearly two hours behind schedule. Mission Control extended the spacewalk beyond its initial 6 1/2-hour duration to squeeze another vital task: replacing three of Hubble?s six batteries, which had not been changed since the telescope launched in 1990.
Massimino had to top off his spacesuit?s oxygen supply so he didn?t run out of air during that final chore, which stretched the orbital work to eight hours and 56 minutes. Good?s spacesuit batteries were his top consumable, but Mission Control told him he had enough for the extended work.
?I don't have that much on internal battery," a tired Good replied. "I'm right on the edge now, but I?m willing to give it a try.?
The gyroscope and battery tasks were NASA?s top priority for the Atlantis? entire 11-day mission since the basic maintenance was crucial in order to keep Hubble running. The flight is NASA?s fifth and final service call to the iconic space telescope.
It was the second of five consecutive excursions to extend the aging Hubble?s orbital life through 2014. A different team of spacewalkers installed a powerful new camera, docking ring and fixed the computer data unit that beams the telescope?s images back to Earth.
?We?re a long way already to greatly extending the longevity of the Hubble observatory,? Hubble?s senior project scientist Dave Leckrone at NASA?s Goddard Space Flight Center told reporters late Friday.
On Saturday, the astronauts will attempt an unprecedented repair for Hubble?s main imager, the Advanced Camera for Surveys, which has been offline since 2007. Another set of batteries will be replaced in a Monday spacewalk.
Massimino had to squeeze his tall frame inside Hubble to replace some of the gyroscopes. At times, both he and Good were wedged in and had to take great care not to bump each other or Hubble?s delicate star trackers near the gyroscopes.
The spacewalk began at 8:49 a.m. EDT (1249 GMT) and ended up being the 8th longest in history.
The astronauts had a brief scare early on when Massimino?s spacesuit radio went out. But he quickly regained radio contact with Atlantis and Mission Control. ?That was scary,? Good said.
?A little bit,? Massimino replied.
The spacewalk ran so long, Mission Control had to push back the Atlantis crew?s bedtime by an hour tonight and give them extra time to sleep in tomorrow. It marked the first spacewalk for Good and the third for Massimino, who ended the day with a total spacewalking time at 22 hours and 42 minutes.
?It was really great going out there today for the first time,? Good said as he thanked his crewmates and Mission Control. ?An incredible effort.?
SPACE.com is providing continuous coverage of NASA's last mission to the Hubble Space Telescope with senior editor Tariq Malik in Houston and reporter Clara Moskowitz in New York. Click here for mission updates, live spacewalk coverage and SPACE.com's live NASA TV video feed.
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