February 13, 2008

Shuttle Astronaut to Return to Spacewalk Duty Today

German astronaut Hans Schlegel will return to spacewalking duty outside the
International Space Station (ISS) Wednesday after sitting out on an earlier excursion
due to a medical issue.

A veteran
European Space Agency (ESA), astronaut Schlegel will step
outside the ISS
on his first spacewalk with crewmate Rex Walheim to replace
an empty nitrogen tank on the space station's metallic backbone-like truss.

"I feel
really great right now," Schlegel told reporters from the flight deck of NASA's
shuttle Atlantis on Tuesday. "I'm, of course, a little bit anxious because
tomorrow is going to be my first [spacewalk]."

managers pulled Schlegel, 56, from the first spacewalk of Atlantis' STS-122
mission — Monday's excursion to help attach the station's
new European Columbus lab
— due to an undisclosed illness. Officials with
NASA, the ESA and Schlegel himself declined to discuss the illness in detail
citing the need for medical privacy.

Schlegel stressed Tuesday that he supported the decision to replace him on
Monday's spacewalk to ensure Columbus, which the astronaut and crewmates opened
for business yesterday
, reached the ISS successfully.

"I didn't
go outside, but I helped from inside and that's the most important thing," said
Schlegel, who helped choreograph the orbital work with shuttle pilot Alan
Poindexter. "We made sure that this [spacewalk] was executed right,
successfully and in a good way."

will also watch over today's spacewalk, which calls for Schlegel and Walheim to
step outside the space station's Quest airlock at 9:35 a.m. EST (1435 GMT). While
the outing marks a first Schlegel, it will be Walheim's fourth foray into the
blackness of space clad only in a NASA-issue spacesuit.

The shuttle
astronauts have a singular goal for today's spacewalk: the replacement of a
so-called nitrogen tank assembly used to charge up the ammonia coolant lines
that shed excess heat through the station's port side radiators. Installed in
2002, the tank has been depleted of its 80-pound (36-kg) supply of nitrogen and
cannot be refilled in orbit.

nitrogen tank weighs around 550 pounds (249-kg) and it is roughly the size of a
small refrigerator," said Anna Jarvis, NASA's lead spacewalk officer for the
STS-122 flight

To swap out
the empty tank, Walheim will ride the space station's Canadarm2 robotic arm
down to the shuttle Atlantis' cargo bay to retrieve its replacement. An orbital
shell game will then follow to swap out the tanks before Walheim can take the
older one back to Atlantis for the return trip home.

"It seems so
easy," Walheim said in a NASA interview.

But the
work is expected to last more than 6 1/2 hours, primarily because of the need
to wrestle with a series of tough bolts, detach and reattach nitrogen lines and
move the station's robotic arm periodically to stay in position. Atlantis
mission specialist Leland Melvin will oversee the robotic arm work from inside
the ISS.

"[It] takes
a fair amount of time, and then doing all the connections in back and doing the
gymnastics of swapping them around," Walheim said. "These are very large

will assist Walheim during the spacewalk, which will include a few extra
cable-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 real
difference at the beginning," said NASA station flight director Bob Dempsey of
the added work. "Otherwise the timeline is pretty much the same. "

by veteran shuttle flyer Stephen Frick, Atlantis' seven-astronaut crew launched
Feb. 7 on what is now a 12-day mission to deliver the Columbus lab to the ISS
and swap out one member of the station's Expedition 16 crew. The shuttle is
scheduled to land on Feb. 19, but could gain an extra 24 hours docked at the station
if mission managers decide later today to extend the spaceflight another day.

spacewalk will begin a 9:35 a.m. EST (1535 GMT). NASA is broadcasting Atlantis'
STS-122 mission live on NASA TV. Click
for SPACE.com's shuttle mission coverage and NASA TV feed.