Astronauts Wrap Up Big Tank Work in Mission's Last Spacewalk
This story was updated at 3:50 p.m. ET.
HOUSTON
- Two shuttle astronauts ventured outside the International Space Station (ISS)
early Tuesday to complete work to install a massive new coolant tank during the
third and last spacewalk of their mission.
Discovery
astronauts Rick Mastracchio and Clayton Anderson
floated outside the station?s Quest airlock at 2:14 a.m. (0614 GMT) for their
last 6 1/2-hour service call on the space station.
Their
first task: Hooking up four hoses to funnel liquid ammonia coolant and nitrogen
for the space station?s onboard systems.
Mastracchio, 50, tackled the job in short order, even
pausing at times while Anderson snapped photos.
?Oh
baby, you?re going to want to take this one to the grandkids,? said Anderson,
51, after taking one particularly
picturesque shot.
It
was quick work for the spacewalkers, but Mission Control hit a snag while
activating the new ammonia tank. A nitrogen valve appeared to be stuck, NASA
officials said.
Space
station flight director Ron Spencer said the stuck nitrogen valve is more than
an annoyance. If Mission Control cannot free it remotely, space station
astronauts will likely have to replace the nitrogen component of the hulking, ammonia
tank, which is the size of a large refrigerator.
The
space station uses nitrogen to pressurize its tanks of liquid ammonia coolant.
It has two spare nitrogen system parts on storage shelves attached to the
orbiting laboratory's backbone-like main truss.
Spencer
said that replacing the nitrogen assembly with a spacewalk is a last resort
since it could be a serious interruption to current shuttle mission, the space
station crew and potentially NASA's next shuttle flight, which is slated to
launch May 14. But if NASA does not fix the problem ? the valve itself can't be
reached by spacewalkers, only its nitrogen system housing ? half of the space
station's systems will have to be switched off.
"We
do have a couple of tricks up our sleeves," Spencer said.
While Mission Control wrangled with the stuck valve during the spacewalk, Mastracchio and Anderson tackled their own obstacle in space. A stubborn bolt held up their work to install an empty ammonia tank (the one they replaced) in Discovery?s payload bay to be returned to Earth.
Bolts have been familiar foes for the astronauts, who have had to use pry bars and brute strength to defeat them on two earlier spacewalks. This bolt was misaligned, and it took both spacewalkers extra time to loosen another bolt, fix the misalignment and retighten everything back in place.
?Great job you guys,? said teacher-astronaut Dorothy ?Dottie? Metcalf-Lindenburger, who choreographed the spacewalk from inside Discovery. ?Now I can finally say good job, we have the ammonia tank in the payload bay.?
Mastracchio and Anderson also had some trouble with the
space station?s airlock hatch at the start of their orbital work. But after
checking the hatch?s handle (to make sure it was in place) they told Mission
Control that all was well.
Discovery?s last spacewalk
The
spacewalk was the sixth career spacewalk for both Mastracchio
and Anderson, and the 143rd spacewalk dedicated to space station assembly since
construction began in 1998.
Both
men have about 38 1/2 hours of spacewalking work under their belts. In all,
they spent 20 hours 16 minutes working outside Discovery and the space station
on this flight.
Tuesday?s spacewalk was also the last ever planned for the shuttle Discovery. When the shuttle next flies to the space station (a delivery mission slated for September), there are no spacewalks planned. That September flight is expected to be the last flight for Discovery and NASA?s final space shuttle mission.?
A couple of hours into the spacewalk, Anderson noticed some wear on one of his spacesuit gloves, but Mission Control said it was no problem unless the bottom layers on the glove were cut.
?I?ve got 51-year-old eyes but it doesn?t look like it?s cut,? Anderson said.
The
astronauts retrieved some unneeded aluminum debris shields from the space
station?s exterior, chores left over from the astronaut duo?s earlier spacewalk
on Sunday.
Anderson was unable to hitch a ride on the station?s Canadian-built robotic arm
to the European Space Agency?s Columbus laboratory to retrieve an experiment
because time was short. Instead, he prepared some tools that would be needed on
NASA?s next shuttle mission in May.
Mastracchio prepared an antenna for installation during
a future shuttle mission, before checking on a beam that was installed during
an earlier spacewalk that flight controllers have noticed wobbling. The astronauts
were spacewalking on the 40th anniversary of the oxygen tank explosion that
crippled the Apollo 13 mission in April 1970.
The
two spaceflyers
made sure to take time to enjoy their work in space, since it could be the last
time they see a shuttle in space from the outside. The views
of Earth from space were astounding, they said.
?Wow,
what a view,? said Anderson.
?It?s
incredible, isn?t it?? Mastracchio replied.
?The Earth is a beautiful place,? Anderson said. ?It?s too bad more people can?t have that view. Maybe, one day.?
Meanwhile,
inside the space station the spacewalkers? crewmates
have been hard at work transferring some of the 17,000 pounds (7,711 kg) of cargo
Discovery hauled to the space station inside its Leonardo cargo pod.
Discovery
blasted off last Monday and is in the midst of a 14-day flight to the International
Space Station and due to land in Florida on April 19.
The
mission is one of NASA?s last few shuttle missions before the fleet is retired
in September. Only three more shuttle flights are scheduled after this
one.
NASA?s
space shuttle fleet is the only spacecraft currently flying that is large
enough to haul parts like the ammonia tanks, which are the size of large
refrigerators, to the International Space Station. Once the fleet is retired
later this year, NASA will be dependent on Russia to ferry astronauts to and
from the station until American commercial spacecraft become available.
President
Barack Obama is expected to
discuss the future of NASA?s
space exploration plan Thursday during a summit in Florida.
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SPACE.com is
providing complete coverage of Discovery's STS-131 mission to the International
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