Japanese astronaut Soichi Noguchi and American crewmate Stephen Robinson returned to the shuttle after spending seven hours and 14 minutes in space, 350 kilometers (220 miles) above Earth.

It was the second spacewalk the pair have carried out during the mission, which has been marred by controversy over the safety of the American shuttles.

Donning bulky space suits, Noguchi and Robinson started the operation at 0842 GMT. It lasted seven hours and 14 minutes.

The main purpose on Monday's walk was to replace one of four gyroscopes which help steer the space station and keep it in its pre-determined orbit. NASA said it had been a complete success.

In a slight change to their program, Noguchi and Robinson also tested an exit hatch in the cargo bay because of "difficulties" they experienced with the hatch after their spacewalk on Saturday, NASA said.

Noguchi rode on the robotic arm attached to the space station to collect the broken gyroscope, take it back to Discovery's cargo bay, and ride back to the truss with a new one. "Oh, the view is priceless," Noguchi said as he moved toward the gyroscope. "I can see the moon."

The two took pictures of each other before returning to the shuttle, which is docked at the space station.

The two did work to a second faulty gyroscope on Saturday and with this work, all four gyroscopes should be working for the first time since 2002.

Noguchi and Robinson are to stage a third space walk on Wednesday. NASA officials have said they may consider repairing material dangling from the bottom of Discovery.

NASA was to announce on Monday whether the repair was necessary and whether Discovery is completely safe to return to Earth.

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