8-hour spacewalk is one of the longest

— -- Spacewalking astronauts had to put a refurbished pair of gyroscopes into the Hubble Space Telescope after a brand new set refused to go in Friday, but scientists were satisfied nonetheless and confident the observatory would point precisely to ever more distant objects in the cosmos.

Replacing the gyroscopes was the top priority of the repair mission, and the struggle had NASA on edge for two hours.

Thanks to the spacewalkers' effort, Hubble ended up with four brand new gyroscopes and two refurbished ones that were original 19-year-old telescope parts, said to be almost as good as the new ones. The telescope also got fresh batteries.

It was the second spacewalk in as many days for the Atlantis astronauts, who once again were bedeviled by problems. On Thursday, another two-man team installed a powerful new camera and a computer data unit, after struggling with a stubborn bolt. NASA had hoped for an easier, less stressful spacewalk, but instead had to endure more drama.

As on Thursday, the astronauts got their work done, but it was harder and took longer than expected. Friday's spacewalk was one of the longest ever, lasting nearly 8 hours, and Mission Control told the weary crewmembers that they could sleep in and start Saturday's spacewalk a little late.

Michael Massimino, who was working from inside Hubble, and his partner, Michael Good, had no problem removing all six of Hubble's 10-year-old gyroscopes. But the last set of new gyroscopes wouldn't fit properly.

Mission Control instructed the men to go get a spare box of gyroscopes from the shuttle, and put that one in. This spare set originally was launched aboard Hubble in 1990 and returned in 1999.

The astronauts successfully installed the refurbished set. By then, however, five hours of the spacewalk had passed and they had yet to start on the other major chore of the day, the battery swap.

The gyroscopes were the No. 1 task, though. Three of the old gyroscopes no longer worked, and two others had been acting up. The other had seen a lot of use.

"My friend Leonidas has a couple of words for you guys that are appropriate right now," shuttle commander Scott Altman told the spacewalkers, referring to the ancient Spartan king. "Remember this day, men, for it will be yours for all time." Then Altman laughed. Leonidas died in battle in 480 B.C.

"We've got a little more work to do, but thanks," replied Massimino.

Hubble's deputy senior project scientist, Mal Niedner, said he was not concerned the astronauts had to resort to refurbished gyroscopes. They lack the latest anticorrosive wiring, but it's "the difference between an A and an A-plus."

In all, five spacewalks are planned so that the observatory — beloved by astronomers and many others for its breathtaking views of the universe — is at its apex while living out its remaining years. Scientists expect the upgraded Hubble to look back even further in time, to within 500 million to 600 million years of creation.

Good drove in the bolts for the gyroscope boxes as Massimino, a returning Hubble mechanic who is over 6-feet tall, worked from inside the telescope, where he had wedged himself in head first. "Trained my whole life for this," he said.

Massimino had a brief scare when his communication system fouled up at the start of the spacewalk. For a minute or two, no one could hear him.

That wasn't the only unnerving thing about this mission.

Space is particularly littered in this 350-mile-high orbit, and Atlantis and its crew face a greater risk of being slammed by a piece of junk. As a precaution, NASA has a rescue shuttle on standby, ready to launch in just three days if necessary.

Even though the spacewalk was running behind, the astronauts pressed on and replaced some batteries.

The hefty, nickel hydrogen batteries that came out were built before the telescope was launched in 1990. They come three to a pack, about the size of a big TV set with a mass of nearly 500 pounds. The final three batteries will be replaced early next week.

The unused new gyroscopes, meanwhile, will be analyzed once they're returned to Earth.

NASA hopes to get another five to 10 years of use out of Hubble, once the Atlantis astronauts plug in all the new equipment. They also will take a crack at fixing two broken science instruments this weekend.

The mission cost NASA more than $1 billion, one-tenth of what has been spent on Hubble over the decades.

What's planned:

•On Saturday, Feustel and astronaut John Grunsfeld will attempt the first-ever repair on a Hubble scientific instrument while in orbit. Fixing the Advanced Camera for Surveys requires them to remove tiny screws that they won't be able to see — while wearing bulky space gloves.

"This will be a nail-biter all the way," Grunsfeld said before Atlantis' May 11 launch.

•On Sunday, astronauts Massimino and Good will try to mend another broken scientific instrument. To bring the Space Telescope Imaging Spectrograph back to life, they'll have to undo more than 110 screws not much bigger than watch screws.

The telescope could be crippled if a single stray screw floats into it.

"I don't know exactly how it's going to turn out," Massimino said before launch. "A lot of miracles have to occur."

The scientific instruments on Hubble — unlike its standard components, such as the observatory's batteries — were not designed to be fixed in orbit. So it's extraordinarily difficult to access them. Hubble's managers decided the two instruments are so scientifically valuable that it's worth the risk to try to repair them.

If the astronauts pull off the repairs, Hubble will have five functional scientific instruments for the first time since 1993, but Hubble's overseers are trying to tamp down expectations.

"On this mission, the final mission, we're going for broke," Leckrone said.

Thursday's spacewalk was not expected to be challenging, but the astronauts encountered an unexpected obstacle as they tried to remove a scientific instrument known as Wide Field Planetary Camera 2.

The camera has been a scientific workhorse, but it's 15 years old, and its replacement will be 15 to 35 times more powerful. Astronomers are eager to start using the new camera.

When Feustel tried to undo the bolt holding the old camera on the telescope, it balked. He tried several combinations of ratchet and power drill, with no luck. For a moment, it looked like the new camera would travel back to Earth rather than remaining on Hubble.

With one tool change and one more application of muscle, Feustel pried the sticky bolt open. "It's been in there for 16 years, Drew, and it didn't want to come out," Grunsfeld said.

"It just decided to be a recalcitrant teenager," said Massimino, who was supervising the spacewalk from inside Atlantis and has two teenage children.

Feustel and Grunsfeld sailed through the installation of a new electronics box to replace one that failed last year, but they ran into trouble again as they tried to install mechanisms to make it easier to open the telescope's access doors.

They successfully installed two, but the third didn't fit properly.

"In traditional Hubble fashion, Hubble threw us a few curves," Grunsfeld said.

Contributing: Traci Watson, USA TODAY; Associated Press