Astronauts hunkered down in an airlock ready for the second space walk of NASA's latest shuttle mission on Sunday, to install more hardware on an orbiting station hundreds of miles above Earth.
The six-hour venture into space was due to start just before 1000 GMT, when US astronauts Scott Parazynski and Daniel Tani will begin moving a truss that supports a set of the station's key solar panels.
The International Space Station (ISS), a giant manned laboratory orbiting 240 miles (390 kilometers) above Earth, is aimed to be a potential jumping-off point for exploration of Mars.
Two astronauts earlier entered Harmony, a newly delivered module on the ISS and began preparing it for its role in connecting two future Japanese and European laboratories to the station.
"Harmony is a very good name for this module," said space station commander Peggy Whitson. "It represents the culmination of a lot of international partner work and will allow international partner modules to be added on."
Italian Paolo Nespoli and Whitson of the United States opened the hatches to the Harmony module at 1224 GMT on Saturday, and along with other crew members spoke to reporters by a video link from inside it.
The bus-size module was attached to the station during the first spacewalk of the mission on Friday.
"Everything is going great," said Rick LaBrode, the mission manager of the Discovery shuttle that blasted the NASA crew into space on Saturday. "We'll continue pressing on. Tomorrow is a great day."
The maneuvring of equipment on Sunday's spacewalk is necessary to prepare the ISS for the arrival of the new laboratories, experts said.
Parazynski and Tani will start by disconnecting cables from the truss. Then astronauts will use the space station's robotic arm to move the truss to an overnight parking position.
Its installation in a new location will be completed during subsequent walks.
The Sunday spacewalkers will also complete external outfitting of Harmony and replace a remote circuit breaker.
To prepare for the walk, Parazynski and Tani were camping out overnight in the station's airlock, NASA officials said.
During Discovery's two-week mission to the ISS, the astronauts are scheduled to perform a record five spacewalks, lasting a total of 30 hours.