Chris Cassidy and Tom Marshburn floated out of the ISS for four hours and 54 minutes, returning to the decompression chamber at 1627 GMT, after completing several maintenance and research tasks during the mission's fifth spacewalk.

The pair secured multi-layer insulation around NASA's mechanical maintenance robot Dextre, split out power channels for two space station gyroscopes and installed video cameras on the front and back of the new Kibo laboratory, which became the station's biggest room when it was installed last year.

They also installed handrails and a portable foot restraint to help future spacewalkers.

Splitting the channels of the two gyroscopes, which provide non-propulsive attitude control for the station, will prevent a failure on one channel from disabling both of the fixtures, the US space agency said.

But the spacewalking duo deferred to another spacewalk "sometime in the future" what was to be their final task -- deploying a payload on another part of the ISS that will provide storage capability for spare space station hardware.

Endeavour is expected to land back on Earth on July 31. The launch of the next shuttle, Discovery, to the ISS is planned for August 18 at 4:25 am (0825 GMT).

During their fourth walk on Friday, Marshburn and Cassidy installed new batteries on one of the oldest of the four solar arrays that power the space station 215 miles (350 kilometers) above Earth.

The six newly fitted batteries "function as expected," the US space agency said, noting that the old batteries were to be taken back to Earth aboard Endeavour.

On Wednesday, NASA had ordered spacewalking astronauts back into the space station 30 minutes early after a spacesuit was found to be working improperly.

Higher than normal carbon dioxide levels were found in Cassidy's spacesuit due to a problem with its lithium hydroxide canister, the space agency said, adding he had not been in any danger.

The carbon dioxide removal unit continued to operate in manual mode Sunday.

Cassidy and his partner Dave Wolf managed to replace only two of the six batteries.

Each ISS battery measures 40 by 36 by 18 inches (101 by 90 by 45 centimeters), weighs 375 pounds (170 kilos) and is designed to last 6.5 years.

Endeavour took off from Cape Canaveral, Florida on July 15 for a 16-day mission with a crew of six Americans and one Canadian to help complete construction of the ISS.

On the second Endeavour spacewalk July 19, the astronauts moved equipment from Endeavour onto the ISS and repaired a malfunctioning toilet on the orbiting station.

During a first spacewalk July 18, astronauts completed construction of the Japanese Kibo science lab during an outing that lasted five and a half hours.

The ISS should be completed in 2010, which is also the target date for the retirement of the US fleet of three space shuttles.

earlier related report
Astronauts begin final spacewalk of Endeavour mission
Two astronauts ventured into open space Monday to install cameras on the International Space Station's new Japanese laboratory during the final spacewalk of the US shuttle Endeavour mission.

Chris Cassidy and Tom Marshburn floated out of the ISS about one hour earlier than planned at 1133 GMT as they began the mission's fifth spacewalk, which was expected to last six and a half hours.

While Mashburn secures multi-layer insulation around the station's two-armed robot, the Special Purpose Dexterous Manipulator known as DEXTRE, Cassidy will separate the power channels shared by two of the station's four gyroscopes.

Splitting the channels of the two gyroscopes, which provide non-propulsive attitude control for the station, will prevent a failure on one channel from disabling both of the fixtures, the US space agency NASA said.

The spacewalking duo will then install video cameras on the front and back of Japan's Kibo laboratory, which became the station's biggest room when it was installed last year.

For their final task, the astronauts will deploy a payload on another part of the ISS that will provide storage capability for spare space station hardware.

During their fourth walk on Friday, Marshburn and Cassidy installed new batteries on one of the oldest of the four solar arrays that power the space station 350 kilometers (215 miles) above Earth.

The six newly fitted batteries "function as expected," the US space agency said, noting that the old batteries were stored on a cargo carrier that will be placed in Endeavour's cargo barrier later in the day.

On Wednesday, NASA had ordered spacewalking astronauts back into the space station 30 minutes early after a spacesuit was found to be working improperly.

Higher than normal carbon dioxide levels were found in Cassidy's spacesuit due to a problem with its lithium hydroxide canister, the US space agency said, adding he had not been in any danger.

The carbon dioxide removal unit continued to operate in manual mode Sunday.

Cassidy and his partner Dave Wolf managed to replace only two of the six batteries.

Each ISS battery measures 40 inches by 36 inches by 18 inches (101 centimeters by 90 centimeters by 45 centimeters), weighs 375 pounds (170 kilos) and is designed to last 6.5 years.

Endeavour took off from Cape Canaveral, Florida on July 15 for a 16-day mission with a crew of six Americans and one Canadian to help complete construction of the ISS.

On the second Endeavour spacewalk July 19, the astronauts moved equipment from Endeavour onto the ISS and repaired a malfunctioning toilet on the orbiting station.

During a first spacewalk July 18, astronauts completed construction of the Japanese Kibo science lab during an outing that lasted five and a half hours.

The ISS should be completed in 2010, which also is the target date for the retirement of the US fleet of three space shuttles.

Endeavour is expected to land back on Earth on July 31. The launch of the next shuttle, Discovery, to the ISS is planned for August 18 at 4:25 am (0825 GMT).

Meanwhile, in yet another deft maneuver Sunday, the space shuttle robotic arm grabbed the Japanese Exposed Section cargo carrier from the space station robotic arm, NASA reported.

Endeavour Commander Mark Polansky and Mission Specialist Julie Payette then used the shuttle arm to place the cargo carrier back into the shuttle payload bay.

The cargo carrier was launched with two science experiments and a communication system that were transferred to the Kibo Exposed Facility earlier in the mission.

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