HOUSTON -- Spacewalkers' specially designed tools couldn't dislodge a balky bolt interfering with repairs Sunday at the Hubble Space Telescope. So they took an approach more familiar to people puttering around down on Earth: brute force.
And it worked. But it set spacewalkers so far behind that they couldn't get all their tasks done.
Atlantis astronaut Michael Massimino couldn't remove one bolt attaching a hand rail to the outside of a scientific instrument he needed to fix. The rail had to be removed or at least bent out of the way.
That was only the beginning of a hard-luck day. The balky bolt and other tiny problems put spacewalkers so far behind schedule that they had to abandon the second part of their spacewalk: replacing some worn insulation on the telescope.
Still, the marathon spacewalk by Massimino and Michael Good took so long — just more than eight hours — that it was the sixth longest U.S. spacewalk. It was a few minutes longer than their Friday spacewalk.
When several tries with different expensive tools couldn't remove the stripped-out bolt, Mission Control in Houston told Massimino to go for the less precise yank.
At Goddard Space Flight Center in Maryland, engineers twice tested that pull on a mock-up before Massimino was told to use his muscles.
"You hope you don't get to the point where you just close your eyes and pull and hope nothing happens," said James Cooper, the Goddard mechanical systems manager for the repair mission. "But we had run out of other options."
Astronauts were careful to tape pieces so they wouldn't fly away and become potential missiles.
"This is like tying branches together in Boy Scouts," Good said.
And while Atlantis was out of video contact 350 miles above Earth, controllers in Houston could only listen as Massimino took a breath and pulled.
After a second of silence, Massimino calmly said: "disposal bag, please."After nearly two hours of work on the balky bolt, astronauts went back to the plan to bring the Space Telescope Imaging Spectrograph back from the dead.
Early test results show the spectrograph, disabled by a power failure five years ago, was brought back to life. But when further tests started, the instrument put itself into "safe mode" because of temperature problems.
Three of the four Hubble spacewalks so far this mission have been delayed by niggling problems, like stubborn bolts and objects that wouldn't fit. A fifth and final spacewalk is set for Monday.
Massimino's run of bad luck only continued. While trying to install a special plate to remove 111 tiny screws that held the instrument cover in place, a tool's battery died. It took more than half an hour for him to go back to the shuttle, swap out batteries and recharge his oxygen supply.
By the time Massimino replaced the internal electronics power supply card in the spectrograph, it was just about the originally scheduled time for the end of the spacewalk. And more than 90 minutes of clean up and close-out work remained.
So spacewalk coordinators on the ground decided that the second part of Sunday's task, the insulation, had to be put off until Monday, if possible.
Not of all the work may get done Monday, but at least part will be attempted, Mission Control said.
"We're very proud of you," Atlantis astronaut John Grunsfeld told the weary spacewalkers.
Grunsfeld and Andrew Feustel will not only pick up some of their work Monday, but they will be the last people to touch the 19-year-old observatory.
On Tuesday, Atlantis will release Hubble. NASA hopes Hubble will keep operating for another five to 10 years, and after that it will be steered to a watery grave.
On Saturday, two other astronauts succeeded with a similar task and revived Hubble's survey camera. Early Sunday, Mission Control told the crew two of the three science channels on the repaired camera were working again.
When NASA planned this mission, officials said it would be a success if either of the two dead instruments could be revived. With Saturday's camera remedy, fixing the spectrograph is a bonus.
The light-separating spectrograph has helped find black holes and examine the atmosphere of planets outside our solar system.
Flying so high without an emergency shelter put the shuttle and astronauts at increased risk of being hit by space debris, so NASA had another shuttle on standby back at its Florida launching site in case a rescue was needed.