Astronauts Set for Third Spacewalk Outside Station

by Tariq Malik, Senior Editor

Date: 08 June 2008 Time: 05:52 AM ET

Astronauts Set for Third Spacewalk Outside Station

Astronaut Mike Fossum, STS-124 mission specialist, waves hello as he participates in the mission's second spacewalk outside the International Space Station on June 5, 2008.
CREDIT: NASA.

HOUSTON — Two astronauts will step outside the International Space Station (ISS) Sunday to pay a service call on the orbiting lab?s cooling system.

Discovery shuttle astronauts Mike Fossum and Ron Garan are slated to begin their spacewalk at about 10:32 a.m. EDT (1432 GMT), marking the third excursion of their mission to the space station, to replace an empty nitrogen tank.

?This is basically a scheduled maintenance,? said Annette Hasbrook, lead space station flight director for Discovery?s STS-124 mission. ?It?s like the 50,000-mile checkup on your car.?

The refrigerator-sized tank is used to pressurize ammonia lines that provide cooling for space station systems.

If time allows, Fossum will revisit the station?s port-side solar array gear, a massive 10-foot (3-meter) wide joint that rotates the station?s left solar arrays like a paddlewheel to track the sun. He spotted what appeared to be grease and gray dust on part of the joint during a Thursday spacewalk and engineers hoped he could collect samples of the material for return to Earth.

?That bearing looks to be in pretty good shape,? Fossum said of the joint.

The port solar array joint has been working fine, but the station?s starboard-side gear has been damaged by metal shavings and used only intermittently since last fall. Fossum?s inspection of port joint, engineers hope, will aid recovery efforts of its starboard counterpart.

Discovery?s seven-astronaut crew is in the middle of a planned 14-day mission to deliver Japan?s $1 billion Kibo research laboratory and swap out one member of the station?s three-man crew.?The shuttle launched May 31 and is scheduled to land on Saturday.

Orbital service call

Garan will spend the bulk of his spacewalking time today perched at the tip of the space station?s 57-foot (17-meter) robotic arm, riding it between work sites as it sweeps from one side of the main truss to the other like a giant windshield wiper blade six stories tall.

?This is going to be an absolutely spectacular [spacewalk],? Garan said in an NASA interview. ?So this maneuver right here takes about 20 minutes, and on the top here I?ll be almost 100 feet above the station, looking straight down at the aft of the station and the Earth 250 miles below. So it?ll be a pretty spectacular view.?

NASA astronaut Karen Nyberg and Japanese spaceflyer Akihiko Hoshide will control the station?s robotic arm during the spacewalk, with Discovery pilot Ken Ham choreographing the work from inside the shuttle. Working together, the astronauts will replace the empty 550-pound (249-kg) nitrogen tank on the station?s starboard truss with a full one currently perched on a port-side spare parts platform.

Fossum and Garan also plan to remove a set of launch restraints and insulation covers from the robotic arm and a window of the station?s new tour bus-sized Japanese Kibo laboratory. They?re also expected to deploy debris shields in the space between the 37-foot (11-meter) module and its rooftop storage module.

The two astronauts are also expected to return a repaired video camera to the station?s exterior during the spacewalk. The excursion will mark the third career spacewalk for Garan and the sixth for Fossum.

?Walking in space is an awesome experience,? Fossum said Saturday. ?It?s unlike anything else you?ll experience anywhere.?

NASA is broadcasting Discovery's STS-124 mission live on NASA TV on Saturday. Click here for SPACE.com's shuttle mission updates and NASA TV feed.