Astronaut John Grunsfeld attaches a tether during a spacewalk Saturday to perform work on the Hubble Space Telescope.

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 an inch-and-a-quarter long bolt attaching a handrail 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. Massimino’s run of bad luck continued when 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.

The 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.

NASA, which prides itself on being prepared, had not anticipated a bolt problem while removing the foot-and-a-half long handrail, said lead flight controller Tony Ceccacci.

Astronomers, whose nerves were tried by the spacewalk, were still happy because it was the second straight resurrection of a much-used but dead scientific device.

“The science capabilities we’ve been given today are fabulous,” Jennifer Wiseman, NASA’s chief of stellar astrophysics said at a late Sunday news conference. “It’s almost like starting with a brand-new observatory.”

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 and a few minutes longer than the one Friday.

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 (bad) 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.