In a daring spacewalk, two space station astronauts cut into the insulation of their descent capsule Thursday and removed an explosive bolt that could have blown off their hands with firecracker force.

Spacewalkers Sergei Volkov and Oleg Kononenko managed, in the end, to safely disconnect the bolt from the Soyuz capsule that will be their ride home this fall. They immediately slid it into a blast-proof container.

"It is in," one of the Russian spacewalkers called out.

"Good. Thank God," someone replied in Russian.

Before the spacewalk, flight controllers in Moscow assured Volkov and Kononenko that the bolt would not explode and that the unprecedented job would help ensure their safe return to Earth in the Soyuz. Nonetheless, Mission Control repeatedly urged them to be careful as they worked near the explosives.

"Take your time," Mission Control warned. "Be careful; be careful, please."

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NASA said that its own engineers were convinced the spacemen would be in no danger, and that it would be all right for them to put the explosive bolt in the blast-proof canister and take it into the international space station for eventual return to Earth.

The past two Soyuz descents have been steep, off-course and bone-jarring, and the Russian Space Agency wants to avoid the problem when Volkov and Kononenko fly home in October. The capsule currently docked at the space station ferried up the two Russians in April.

Kononenko used a serrated knife to cut away the thick shiny insulation surrounding the bolt — a tool normally shunned by spacewalkers because of the possibility of piercing their pressurized suits or gloves. It was a messy job, with shreds of the multilayer insulation floating every which way.

Next, the astronauts installed devices to eliminate static electricity, struggling at times in the small, cramped area. Finally, four hours into the spacewalk, Volkov pulled out a socket wrench and removed the 3-inch (7.6-centimeter) pyrotechnic bolt, one of 10 used to separate two parts of the module during re-entry.

During Soyuz descents this past April and in October 2007, these two sections did not separate properly, leading to so-called ballistic entries that subjected the crews to far higher gravity forces than normal.

Russian engineers suspect some of the explosive bolts did not fire. By disabling the bolts in this suspect location, there should be no mechanical hang-up during the October descent, officials said.

The lone American on board, Gregory Chamitoff, was inside the Soyuz for the entire six-hour spacewalk in case an emergency required the two Russians to join him in the capsule. Chamitoff took books, music and a laptop computer with him to while away the time, and could hear everything that was going on.

Each pyrotechnic bolt has the force of a large firecracker, NASA officials said.

A high-ranking flight director at Russian Mission Control outside Moscow told the crew Wednesday that the bolt could withstand shocks of up to 100 times the force of gravity and would not fire, even if they hit it with a big hammer. "You should not be concerned at all," he said.

The blast-proof container is made of stainless steel. It will remain sealed, with the bolt inside, until it is returned to Earth aboard the Soyuz for analysis.

"We dream of a lot of wild things to do, and after much analysis, sometimes we do them and sometimes we don't," Mike Suffredini, NASA's space station program manager, said earlier this week.

"We have quite a bit of confidence in this particular case that we're perfectly safe," Suffredini told reporters.

NASA has a keen interest in the Russian-built Soyuz capsules because they sometimes transport Americans to and from the space station, and also serve as lifeboats. Once the space shuttles are retired in 2010, the Soyuz will be the sole means of human space transportation until 2015, when America's new rocketship starts carrying crews.

Before floating back inside, Volkov and Kononenko attached a patch over the cut insulation on the Soyuz. As they wrapped up their work, Mission Control congratulated the pair and noted that Volkov was now "a full-blown crew commander" with his own grenade.

The two Russians will take another spacewalk Tuesday to perform much more routine space station work.