HOUSTON — Two spacewalking astronauts are set
to venture outside the International Space Station (ISS) tonight for a marathon
spacewalk to attach twin arms to a giant robot.
Space
shuttle Endeavour astronauts Rick Linnehan and Mike Foreman will spend around
seven hours in the vacuum of space installing the arms of Dextre, a 1.7-ton maintenance
robot built by the Canadian Space Agency (CSA). The spacewalking duo's on-orbit
construction work is scheduled to begin at 8:23 p.m. EDT (0023 GMT March 16).
Garrett
Reisman, a space station flight engineer who helped Linnehan latch on Dextre's
gripper-like hands during Wednesday's late-night spacewalk, said today is the
big day for "Mr. Dextre."
"They're
going to assemble almost the entire robot," Reisman told SPACE.com
during an on-orbit interview Saturday morning. "The arms will go on, the
shoulders will rise up out of the pallet and it's going to be really exciting."
Tonight's
extravehicular activity, or EVA, will be the second of five planned for
Endeavour's 16-day mission — NASA's longest planned flight to the ISS in
history. The spacewalk itself will also be the longest of the mission at seven
planned hours.
Strong
arms
The
spacewalkers' first task outside of the Quest airlock will be to remove protective
covers and cables on Dextre's arms. Once removed, the two will be able to begin
installing two seven-jointed limbs onto the robot's 12-foot (3.7-meter) body.
Linnehan will
latch his feet onto the end of the space station's robotic arm, from which
he'll pull Dextre's limbs from a pallet containing the robot's pieces. Each arm
will then be temporarily attached to the outside of the pallet with Foreman's
help.
Yet weighing
in at a colossal 775 pounds a piece — as much as a full-grown moose — shuffling
the 11-foot (3.4-meter) arms is no small feat.
"There's
definitely some skill and technique they've had to develop to handle those
loads," Zebulon Scoville, lead spacewalk officer for the STS-123 mission, said
of the astronauts during a preflight briefing.
"Dextre
will [then] be pivoted up 60 degrees, where he'll snap into position,"
said Pierre Jean, program manager for the CSA's space station program.
In this
position, Linnehan and Foreman will have enough clearance to install each giant
arm. "This is when Dextre gives a 'V' for 'victory,'" Jean said of
Dextre's completed 30-foot (9-meter) arm span.
Helper
bot
Reisman
said Dextre possesses human-like characteristics, and it's no accident.
"He's
got two arms, a body, a head and he is designed to basically do the same things
that we do on a spacewalk," Reisman said.
Using extremely
touch-sensitive hands and lanky yet powerful arms, the Dextre robot will be able to unscrew,
remove, stow, and replace components around the space station as small as a
phonebook to as large as a phone booth.
Such
abilities will limit the number of dangerous spacewalks astronauts perform outside
the space station, Reisman added.
"He'll
be a great helper for us," he said, noting that Dextre will also be able
to fetch items around the space station and carry them to spacewalking
astronauts. "He'll be able to set the scene for us, carry all the big
bulky stuff that's hard for us to carry."
Powered
up
Although
Dextre's assembly has gone smoothly so far, a flawed cable in the robot's
pallet cut off the flow of vital electrical
power needed to warm its circuits in the cold of space.
With the
robot's circuits in danger, engineers on the ground worked Thursday morning
through late Friday evening to devise plans to route power into Dextre's many pieces.
After a software upgrade failed to help, astronauts on board the space station
grappled the robot's head Friday evening and successfully provided power to the
robot's heaters.
"I
think Dextre is doing much better today, much warmer than the last time I was
out there with him," Reisman said. "What I look forward to most is
seeing Dextre come to life."
Following
tonight's spacewalk, set to wrap up around 3:28 a.m. EDT (0728 GMT) Sunday
morning, three remaining EVAs remain. Linnehan and Foreman will work in pairs
with mission specialist Bob Behnken to finish Dextre and install it, perform
on-orbit experiments, test a goo gun-like heat shield repair device and stow
Endeavour's sensor-tipped inspection boom on the space station for a later shuttle
mission.
Endeavour and its seven-astronaut crew launched from Cape Canaveral, Fla., on March 11 and docked at the space station on March 13. The 100-ton orbiter is scheduled
to make its return to Earth on March 26.
SPACE.com
senior editor Tariq
Malik contributed to this story from New York City.
NASA is
broadcasting Endeavour's STS-123 mission live on NASA TV. Click here for SPACE.com's
shuttle mission coverage and NASA TV feed.
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