HOUSTON —
Two astronauts floated outside the International Space Station (ISS) Sunday on
their mission's last spacewalk to make a cooling system service call and wrap up work on its new Japanese lab.
Spacewalkers
Michael Fossum and Ronald Garan replaced a refrigerator-sized tank filled with
nitrogen to pressurize the station's ammonia cooling lines.
But the
seemingly mundane maintenance task gave Garan two grand views of Earth and space from the
tip of the station's 57-foot (17-meter) robotic arm as he toted first the
empty 550-pound (249-kg) tank, and then its replacement, from one end of the station
to the other. NASA likened the maneuver to that of a giant windshield wiper.
"A lot
different with the planet down there," Garan said from his perch 80 feet (24
meters) above the space station and 215 miles (346 km) above Earth.
"Isn't it a
great view," Fossum asked as the station flew high over Peru.
"Unbelievable,"
Garan replied.
NASA
astronaut Karen Nyberg and Japanese spaceflyer Akihiko Hoshide flew the
station's robotic arm for Garan from inside the orbiting lab. Discovery shuttle pilot
Ken Ham choreographed the work from inside the docked orbiter's flight
deck.
The two
astronauts began their spacewalk at 9:55 a.m. EDT (1355 GMT) just a few minutes
before dawn over the southern Pacific Ocean just off the coast of Peru. It was
the third of NASA's STS-124 mission to deliver Japan's massive, $1
billion Kibo laboratory and a new crewmember to the space station.
In addition
to swapping out the nitrogen tank, Fossum and Garan removed insulation covers
and restraints from a window and the robotic arm of Japan's new tour bus-sized
Kibo laboratory. They also deployed a set of metal shields between the 37-foot
(11 meter) lab and its smaller
storage attic to protect against damage from orbital debris or tiny space
rocks.
The
spacewalkers worked swiftly, starting out more than a half hour early and
completing all their main tasks plus a few extra chores.
One extra
task sent Fossum to the station's port side solar array rotary joint, a 10-foot
(3-meter) wide gear designed to spin the station's left solar wings like a
paddlewheel to track the sun. He collected a sample of some gray dust-like
material that he first spotted last week in a Thursday spacewalk.
The port
solar array joint is working fine, but engineers on Earth hope that the samples
collect by Fossum will help ongoing efforts to repair a similar gear on the
starboard side that been damaged by metal shavings.
Sunday's
spacewalk marked the 112th excursion dedicated to space station construction
and the last of three spacewalks planned for Discovery's
STS-124 mission. Fossum and Garan spent a total of 20 hours and 32 minutes
working outside the station during their three spacewalks.
The
spacewalk was the sixth career excursion for Fossum, who ended with a total of
42 hours and one minute of spacesuit-clad work. He now ranks 12th on the list
of all time spacewalkers. The three STS-124 spacewalks were the first for
Garan, who is also making his first spaceflight on the mission.
"Well,
there are the stars," Garan said during one of his robotic arm rides as he
peered out into the depths of space.
Fossum said
a young student once asked him if it actually was possible to see the stars
while working on a spacewalk.
"I told him
I never had the chance to turn my lights off and look," he said. "Indeed, you
can."
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.
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