HOUSTON —German astronaut Hans Schlegel will return to spacewalking duty outside theInternational Space Station (ISS) Wednesday after sitting out on an earlier excursiondue to a medical issue.
A veteranEuropean Space Agency (ESA), astronaut Schlegel will stepoutside the ISS on his first spacewalk with crewmate Rex Walheim to replacean empty nitrogen tank on the space station?s metallic backbone-like truss.
?I feelreally great right now," Schlegel told reporters from the flight deck of NASA?sshuttle Atlantis on Tuesday. ?I?m, of course, a little bit anxious becausetomorrow is going to be my first [spacewalk].?
Missionmanagers pulled Schlegel, 56, from the first spacewalk of Atlantis? STS-122mission — Monday?s excursion to help attach the station?snew European Columbus lab — due to an undisclosed illness. Officials withNASA, the ESA and Schlegel himself declined to discuss the illness in detailciting the need for medical privacy.
ButSchlegel stressed Tuesday that he supported the decision to replace him onMonday?s spacewalk to ensure Columbus, which the astronaut and crewmates openedfor business yesterday, reached the ISS successfully.
?I didn?tgo outside, but I helped from inside and that?s the most important thing,? saidSchlegel, who helped choreograph the orbital work with shuttle pilot AlanPoindexter. ?We made sure that this [spacewalk] was executed right,successfully and in a good way.?
Poindexterwill also watch over today?s spacewalk, which calls for Schlegel and Walheim tostep outside the space station?s Quest airlock at 9:35 a.m. EST (1435 GMT). Whilethe outing marks a first Schlegel, it will be Walheim?s fourth foray into theblackness of space clad only in a NASA-issue spacesuit.
The shuttleastronauts have a singular goal for today?s spacewalk: the replacement of aso-called nitrogen tank assembly used to charge up the ammonia coolant linesthat shed excess heat through the station?s port side radiators. Installed in2002, the tank has been depleted of its 80-pound (36-kg) supply of nitrogen andcannot be refilled in orbit.
?Thenitrogen tank weighs around 550 pounds (249-kg) and it is roughly the size of asmall refrigerator,? said Anna Jarvis, NASA?s lead spacewalk officer for theSTS-122 flight.
To swap outthe empty tank, Walheim will ride the space station?s Canadarm2 robotic armdown to the shuttle Atlantis? cargo bay to retrieve its replacement. An orbitalshell game will then follow to swap out the tanks before Walheim can take theolder one back to Atlantis for the return trip home.
?It seems soeasy,? Walheim said in a NASA interview.
But thework is expected to last more than 6 1/2 hours, primarily because of the needto wrestle with a series of tough bolts, detach and reattach nitrogen lines andmove the station?s robotic arm periodically to stay in position. Atlantismission specialist Leland Melvin will oversee the robotic arm work from insidethe ISS.
?[It] takesa fair amount of time, and then doing all the connections in back and doing thegymnastics of swapping them around,? Walheim said. ?These are very largecomponents.?
Schlegelwill assist Walheim during the spacewalk, which will include a few extracable-connecting chores leftover from Monday?s excursion. If they have additional time, they may also cover a set of trunnions pins aboard the Columbus lab in insulation.
?The only realdifference at the beginning,? said NASA station flight director Bob Dempsey ofthe added work. ?Otherwise the timeline is pretty much the same. ?
Commandedby veteran shuttle flyer Stephen Frick, Atlantis? seven-astronaut crew launchedFeb. 7 on what is now a 12-day mission to deliver the Columbus lab to the ISSand swap out one member of the station?s Expedition 16 crew. The shuttle isscheduled to land on Feb. 19, but could gain an extra 24 hours docked at the stationif mission managers decide later today to extend the spaceflight another day.
Today?sspacewalk will begin a 9:35 a.m. EST (1535 GMT). NASA is broadcasting Atlantis'STS-122 mission live on NASA TV. Clickhere for SPACE.com's shuttle mission coverage and NASA TV feed.
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