Emergency Christmas Eve spacewalk a success
Two astronauts successfully installed a replacement coolant
pump aboard the International Space Station Tuesday,
wrapping up a high-stakes two-spacewalk repair job and clearing the way for
flight controllers to re-activate a critical coolant system.
"No, thank you guys," astronaut Doug Wheelock replied from mission
control in Houston. "It's the best Christmas ever. Thanks, guys."
"Yeah, I'd just like to add to that," Mike Hopkins said from the
airlock. "Fantastic work, Merry Christmas to everybody. It took a couple
of licks to get her done, but we got it."
The only problem of any significance during the seven-hour 30-minute spacewalk
was trouble getting one of four ammonia lines disconnected from a so-called
jumper box where it was temporarily plugged in during a spacewalk Saturday.
Hopkins and Mastracchio finally freed a quick-disconnect fitting holding the
half-inch line in place, and were sprayed with ammonia ice crystals trapped in
the connector. The toxic chemical posed no threat to the astronauts, but they
spent a few extra minutes in vacuum to ensure any ice stuck to their suits had
time to dissipate before they re-entered the station.
"Good news! The thermal control officer reports a good bump start test on
the newly installed pump module," NASA's mission control commentator, Rob
Navias, reported. "We have a pump that is alive and well."
Flight controllers plan to begin re-activating coolant loop A,
clearing the way to restart scientific experiments and other hardware that was
shut down when the coolant loop suffered a malfunction Dec. 11.
The successful spacewalk also clears the way for Expedition 38 commander Oleg
Kotov and Russian flight engineer Sergey Ryazanskiy to carry out a spacewalk of
their own on Friday. They plan to venture outside to
mount cameras on the hull of the Zvezda command module as part of a commercial
venture to beam down high-definition Earth views to subscribers around the
world.
Tuesday's spacewalk was the 258th by U.S. astronauts, the 176th devoted to
station assembly and maintenance since construction began in 1998, the 10th so
far this year, the eighth for Mastracchio and the second for Hopkins.
The goal of Tuesday's outing was to install a replacement ammonia pump module in
coolant loop A, one of two cooling systems used to dissipate the heat generated
by the station's electrical systems. A valve in the loop A pump assembly
malfunctioned Dec. 11, partially disabling the system and forcing flight
controllers to power down non-essential systems.
More important, the malfunction left the station one failure away from a much
more drastic powerdown should the lone operational coolant loop break down.
During a five-hour 28-minute spacewalk Saturday,
Mastracchio and Hopkins disconnected the suspect ammonia pump module on the
right side of the station's main power truss, pulled it from its slide-in rack
in the S1 segment of the truss and mounted it on a nearby storage fixture to
complete phase one of the coolant system repair job.
As a result, Mastracchio assembled a different suit for the second spacewalk
while Hopkins used the one he wore Saturday, the same
suit that developed a potentially dangerous leak during a July spacewalk.
After exhaustive troubleshooting, engineers concluded the leak was caused by contamination
that clogged a filter. While the root cause of the contamination has not yet
been determined, the astronauts replaced suspect components and both suits
performed normally during both coolant repair spacewalks.
During their second spacewalk Tuesday, Mastracchio and
Hopkins focused on installing the replacement pump module.
In spectacular video downlinked from the station, Mastracchio and Hopkins,
anchored to the end of the station's robot arm, could be seen unbolting the
spare pump module from its storage pallet and pulling it from its insulated
enclosure.
"Looks like you're almost there," Mastracchio radioed as arm-operator
Koichi Wakata, working inside the Destiny lab module, slowly pulled Hopkins and
the pump assembly away. "You're out of the groove there, Mike, I think
you're in charge now of the pump module. ... It's stable, Mike, it looks good,
you're doing a great job, it looks beautiful."
Hopkins held the tethered pump module in his gloved hands as Wakata slowly
moved him inboard from the storage pallet on the S3 truss segment to the pump's
install location in the S1 segment.
The astronauts then guided the big module into place and drove home bolts to
lock it down. They had no trouble hooking up the first two ammonia lines, known
as M1 and M2. Another two lines, M3 and M4, were attached to a jumper box Saturday to allow the ammonia in the coolant loop to expand
and contract as needed when the station flew into and out of sunlight.
The astronauts initially were unable to disconnect the half-inch-wide M4 line
from the jumper box. Mastracchio retrieved a tool designed to apply additional
force to the quick-disconnect bale holding the mechanism together. The idea was
to push the lever far enough over to allow the astronauts to depress a locking
button, allowing them to separate the two sides of the fitting.
But the stubborn fitting refused to cooperate.
"One thing we never expected," Mastracchio muttered at one point.
After positioning the quick-disconnect tool with varying degrees of force,
flight controllers decided to lower the pressure in the line. Right around that
point, the astronauts successfully demated the stubborn fitting, but reported,
"We do have snow coming out."
A few moments later, astronaut Douglas Wheelock in mission control asked the
spacewalkers if ammonia was still leaking out "or has it dissipated."
"Yes. It's about one every second, one little snowflake a second,"
Mastracchio replied.
Asked if their spacesuits had been hit by any ice, Mastracchio said
"absolutely," adding a few moments later "they are just
completely drowning us now."
"Copy, Rick," Wheelock said. "And we have no video, Rick, so
we'll just take your continued description."
"OK. They're pretty good size particles, much bigger than anything we've
ever seen. See that big one going by you, Mike?"
"I do," Hopkins said.
"It looks like they're coming inboard of the pump module, all around the
pump module, looks like," Mastracchio said.
"I can't see it
everywhere, where the light is, but they're hitting the wrist cluster of the
SSRMS (robot arm), they're enveloping Mike, probably enveloping me, also."
"Yes they are," Hopkins said. "Big chunks, big chunks."
The ammonia presumably was trapped in the line and expelled when flight
controllers sent commands to vent the jumper box. The leak rate diminished a
few moments later and the astronauts pressed ahead with work to attach M4 and
then M3 to the replacement pump module.
The ammonia posed no threat to the spacewalkers, but they had to spend a few
extra minutes in vacuum to give any ice crystals that may have stuck to their
suits time to dissipate. Decontamination procedures have been required during
past spacewalks involving the ammonia coolant system to make sure returning
spacewalkers don't introduce any toxic material into the station's air supply.
NASA originally held open the possibility of a third spacewalk to complete the
coolant system repair work, but with the successful pump installation and
activation Tuesday, the station crew now can look forward to a quiet Christmas in orbit before making preparations for the
Russian spacewalk Friday.
