Two astronauts returned from open space on Monday after installing cameras on the International Space Station's new Japanese laboratory during the final spacewalk of the space shuttle Endeavour mission.

Chris Cassidy and Tom Marshburn floated out of the ISS for four hours and 54 minutes, returning to the decompression chamber at 4.27pm 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 31 July. The launch of the next shuttle, Discovery, to the ISS is planned for 18 August.

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 345 kilometres 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 on 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, weighs 375 pounds and is designed to last 6.5 years.

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

During a first spacewalk 18 July, 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.