HOUSTON — Two spacewalking astronauts are setto venture outside the International Space Station (ISS) tonight for a marathonspacewalk to attach twin arms to a giant robot.
Spaceshuttle Endeavour astronauts Rick Linnehan and Mike Foreman will spend aroundseven hours in the vacuum of space installing the arms of Dextre, a 1.7-ton maintenancerobot built by the Canadian Space Agency (CSA). The spacewalking duo's on-orbitconstruction work is scheduled to begin at 8:23 p.m. EDT (0023 GMT March 16).
GarrettReisman, a space station flight engineer who helped Linnehan latch on Dextre'sgripper-like hands during Wednesday's late-night spacewalk, said today is thebig day for "Mr. Dextre."
"They'regoing to assemble almost the entire robot," Reisman told SPACE.comduring an on-orbit interview Saturday morning. "The arms will go on, theshoulders will rise up out of the pallet and it's going to be really exciting."
Tonight'sextravehicular activity, or EVA, will be the second of five planned forEndeavour's 16-day mission — NASA's longest planned flight to the ISS inhistory. The spacewalk itself will also be the longest of the mission at sevenplanned hours.
Thespacewalkers' first task outside of the Quest airlock will be to remove protectivecovers and cables on Dextre's arms. Once removed, the two will be able to begininstalling two seven-jointed limbs onto the robot's 12-foot (3.7-meter) body.
Linnehan willlatch his feet onto the end of the space station's robotic arm, from whichhe'll pull Dextre's limbs from a pallet containing the robot's pieces. Each armwill then be temporarily attached to the outside of the pallet with Foreman'shelp.
Yet weighingin at a colossal 775 pounds a piece — as much as a full-grown moose — shufflingthe 11-foot (3.4-meter) arms is no small feat.
"There'sdefinitely some skill and technique they've had to develop to handle thoseloads," Zebulon Scoville, lead spacewalk officer for the STS-123 mission, saidof the astronauts during a preflight briefing.
"Dextrewill [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 thisposition, Linnehan and Foreman will have enough clearance to install each giantarm. "This is when Dextre gives a 'V' for 'victory,'" Jean said ofDextre's completed 30-foot (9-meter) arm span.
Reismansaid Dextre possesses human-like characteristics, and it's no accident.
"He'sgot two arms, a body, a head and he is designed to basically do the same thingsthat we do on a spacewalk," Reisman said.
Using extremelytouch-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 aphonebook to as large as a phone booth.
Suchabilities will limit the number of dangerous spacewalks astronauts perform outsidethe space station, Reisman added.
"He'llbe a great helper for us," he said, noting that Dextre will also be ableto fetch items around the space station and carry them to spacewalkingastronauts. "He'll be able to set the scene for us, carry all the bigbulky stuff that's hard for us to carry."
AlthoughDextre's assembly has gone smoothly so far, a flawed cable in the robot'spallet cut off the flow of vital electricalpower needed to warm its circuits in the cold of space.
With therobot's circuits in danger, engineers on the ground worked Thursday morningthrough 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 stationgrappled the robot's head Friday evening and successfully provided power to therobot's heaters.
"Ithink Dextre is doing much better today, much warmer than the last time I wasout there with him," Reisman said. "What I look forward to most isseeing Dextre come to life."
Followingtonight's spacewalk, set to wrap up around 3:28 a.m. EDT (0728 GMT) Sundaymorning, three remaining EVAs remain. Linnehan and Foreman will work in pairswith mission specialist Bob Behnken to finish Dextre and install it, performon-orbit experiments, test a goo gun-like heat shield repair device and stowEndeavour's sensor-tipped inspection boom on the space station for a later shuttlemission.
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 scheduledto make its return to Earth on March 26.
SPACE.comsenior editor TariqMalik contributed to this story from New York City.
NASA isbroadcasting Endeavour's STS-123 mission live on NASA TV. Click here for SPACE.com'sshuttle mission coverage and NASA TV feed.
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