Second Endeavour shuttle spacewalk gets underway

US astronaut Bob Behnken and his British-born partner Nicholas Patrick switched their suits to battery power, officially marking the start of the 6.5 hour spacewalk, at 9:20pm (0220 GMT Sunday), about 10 minutes behind schedule.

The pair will continue the work they started on their first walk Thursday, attaching the Tranquility node and observation cupola to the International Space Station.

Nasa said the two astronauts would spend their first four hours connecting ammonia loops on the Tranquility node to those of the Destiny laboratory.

Behnken will then open one of the loops so that ammonia can flow to the node from the station's external thermal control system, the US space agency said.

Nasa also said Saturday that mission managers had approved the addition of an extra day to the Endeavour's flight.

"That day, which will be a new Flight Day 11 beginning Wednesday afternoon, will be used to relocate two Water Recovery System racks, the Waste Hygiene Compartment and the Oxygen Generation System into Tranquility," the space agency said on its website.

"Those relocations were on hold pending the repairs conducted earlier in the flight, and enough run time on the system to generate needed samples for return to Earth for analysis."

The addition brings the length of the mission to 14 days, and moves the shuttle's expected landing date to February 21.

Behnken, Patrick and others aboard the ISS have so far been denied the out-of-this-world view that the observation cupola attached to Tranquility promises to deliver.

Nasa said shutters on the cupola's seven windows would be opened Tuesday, finally providing a panoramic view of space, Earth and visiting spacecraft, but also vital access for monitoring space walks and docking operations.

The cupola can accommodate two crew members at a time and is equipped with portable workstations that can control station and robotic activities.