(Updates with end of spacewalk)

By Irene Klotz

CAPE CANAVERAL, Fla., July 10 (Reuters) - Two spacewalking cosmonauts delicately removed an explosive bolt from their Soyuz capsule on Thursday in hopes engineers can figure out why two previous crews landed hard and off course.

The bolt, which has the explosive capability of an M-80 firework, is one of 10 that separate the Soyuz's crew module from an equipment compartment before entry into Earth's atmosphere.

Russian engineers suspect a bad bolt delayed the compartment's jettison during landings in October 2007 and April 2008, leading to steep and fast descents and hard slams into the ground.

The bolt removed by cosmonauts Sergei Volkov and Oleg Kononenko was sealed inside a blast-proof canister and will be returned home aboard the Soyuz when the crew completes its mission in October.

Despite assurances the bolt could not detonate in the cosmonauts' hands, flight controllers repeatedly cautioned the men to move slowly and carefully.

"Take your time," Mission Control, speaking through a translator, told the spacewalkers.

It took four hours for Volkov and Kononenko to position themselves at the Soyuz, cut through insulation and open a locking mechanism to free one of the bolts.

Finally, at 6:44 p.m. EDT, Volkov handed the device to Kononenko, who was standing by with a stainless-steel, blast-proof canister.

"It is in," one of the cosmonauts said. "Thank God."

The six-hour,18-minute outing was the first for both Volkov, the station's commander and Kononenko, the lead flight engineer, both of whom flew to the outpost in April

Their crewmate, NASA astronaut Greg Chamitoff, who joined them last month, was inside the Soyuz during the spacewalk to avoid being cut off from an escape route to the ship should a problem arise.

"We do not like to separate the crew from (the) escape vehicle," flight director Bob Dempsey told reporters before the spacewalk. "Therefore Greg will be staying in there. He will have some laptops, books and computers to work on while he's there."

Chamitoff will return to the Soyuz again on Tuesday while his crewmates make a second spacewalk to prepare the station for another docking port. Next year, the station's crew size is expected to double from three to six, meaning a second Soyuz will need to be parked at the outpost so everyone has a ride back to Earth. A Soyuz can hold three people. (Editing by Todd Eastham)

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