WASHINGTON, Aug. 1 (Xinhuanet) -- Two astronauts of the US shuttle Discovery started their second of three spacewalks early on Monday to replace a failed spinning wheel of the international space station.

    Astronauts Stephen Robinson and Soichi Noguchi moved into the shuttle's airlock and switched on their autonomous electrical batteries at 3:42 a.m. (0842 GMT), starting the second spacewalk of the mission.

    During their more than six hours stay in the space, the two will be tasked with replacing a gyroscope, one of the four spinning devices that help steer the international space station. The 300 km gyroscope stopped working in 2002.

    On Saturday, the two astronauts carried out their first spacewalk of the mission and restored power to another gyroscope which stopped spinning in March.

    Once the task of their second spacewalk is successfully fulfilled, the four gyroscopes of the space station will be expected to work simultaneously for the first time in around three years.

    In a slight adjustment to their task, the two astronauts will also check the exit hatch after they experienced minor problems while closing the hatch during their previous spacewalk.
    As Robinson and Noguchi float in the space, other members of the flight will continue their job of transferring supplies between the shuttle and the international space station. Enditem