Liz Austin Peterson

Two astronauts set out yesterday for the second spacewalk of Discovery's mission to the international space station.

They aim to add equipment to the outside of the new Harmony module and to inspect areas of concern on the orbiting outpost.

Spacewalkers Scott Parazynski and Daniel Tani will detach a 15-ton girder. Astronauts inside the station will use a robotic arm to move it to a temporary location.

Parazynski will then install spacewalking handrails and other equipment to the outside of Harmony, a chamber the size of a school bus, that was delivered by the shuttle Discovery and installed in the mission's first spacewalk. The crew entered the room for the first time on Saturday.

Tani will check for possible sharp edges on a rail for the robot arm. Nasa had to cut a spacewalk short during Endeavour's August mission after an astronaut noticed a quarter-inch-long rip in his glove. Mission control said sharp edges might have caused it.

Tani will later help Parazynski install a fixture on Harmony for the station's robotic arm to move the compartment to its permanent home. The space station's crew will relocate Harmony after Discovery leaves in another week.

The European Space Agency's science laboratory, Columbus, will hook on to Harmony in December. The Japanese Space Agency's lab called Kibo, meaning Hope, will latch on early next year.

Harmony will function as a nerve centre, providing air, electricity and water for the space station. It was launched with racks of computer and electronic equipment pre-installed. All this had to be locked down for the rocket ride to orbit, leaving the astronauts to undo 700 bolts. - Sapa