Mastracchio and Mike Hopkins switched their spacesuits to battery power
early Saturday, kicking off the first in a series of spacewalks to
replace a refrigerator-size ammonia pump assembly aboard the
Space Station in a high-stakes attempt to restore a critical coolant
Floating in the station's
Quest airlock module, the astronauts began the planned six-and-a-half-hour
excursion at 7:01 a.m. EST as the space station sailed 250 miles above the Atlantic Ocean
"Quite a view,"
Hopkins marveled as he floated outside the airlock to begin his first
"Yeah, watch that
first step," joked Mastracchio, making his seventh EVA, shorthand for extravehicular
Mastracchio, call sign EV-1, is wearing a suit with red stripes and using
helmet camera No. 20. Hopkins, EV-2, is wearing an unmarked suit with helmet
camera No. 18. This is the 175th spacewalk devoted to station assembly and
maintenance since construction began in 1998 and the ninth so far this year.
The spacewalks were
ordered after a critical valve in one of the space station's two coolant loops
malfunctioned last week, resulting in lower-than-allowable temperatures.
While coolant loop A remained
partially operational, flight controllers were forced to shut down a variety of
systems in the station's forward modules, including experiment hardware, to
keep those systems from over heating. Coolant loop B remained fully functional.
Engineers attempted to
resolve the problem using a software patch to precisely control the position of
another valve in the coolant system, and thus the temperature of the ammonia in
loop A. But NASA managers ultimately opted for a series of spacewalks to
replace the ammonia pump module where the suspect flow control valve is
The pump module in
question was installed during three 2010 spacewalks after the pump in the
original assembly broke down, taking out coolant loop A in its entirety. This
time around, the loop A pump is working normally, cooling components mounted
outside the station's habitable modules. But the faulty flow control valve is
preventing the loop from cooling components mounted inside the habitable
Two hours and 20 minutes
into the spacewalk, Mastracchio and Hopkins were in the process of
disconnecting ammonia coolant lines.
The loop A pump
module is located on the right side of the station's solar power truss.
Mastracchio is anchored to the end of the station's robot arm while Hopkins is
The refrigerator-size pump
module is plumbed into the loop with three 1.5-inch-wide ammonia lines,
referred to as M1, M2 and M3, and a one-half-inch line, known as M4. All four
had to be disconnected, along with five electrical cables.
quick-disconnect fittings are locked in place with complex mechanisms that
feature so-called "spool positioning devices," or SPDs, that ensure
proper alignment or both sides, levered handles that can pull the connector
components together or force them apart, locking collars and safety buttons
that must be depressed before the components can be disengaged.
During a pump module
replacement in August 2010, another team of astronauts ran into major problems
getting one of the ammonia lines disconnected, presumably because of pressure
in the system. This time around, flight controllers reduced the pressure in the
loop before the spacewalk began to prevent any similar problems.
Ammonia lines M3 and M4
were the first to get disconnected. Both needed to be plugged into a so-called
"jumper" box to allow the ammonia in coolant loop A to expand and
contract as the station moves into and out of sunlight during the course of the
pump replacement work.
Mastracchio had no
problems disconnecting M3 and M4, reporting a small amount of ammonia ice
crystals, or flakes, floating out of the connectors.
"I do see some snow,
very little," he said, "very small flakes. Coming from the forward
side of the QD. Very small flakes, if you will, and now I don't see them any
more. Very, very small particles."
"Copy that, Rick, and
can you tell if any of that hit your suit?" astronaut Doug Wheelock asked
from mission control.
"I think yes,"
Mastracchio replied. A few moments later, after disconnecting the M3 line, he
reported "a few more flakes coming out, not too bad though. ... Looks like
the male QD is kind of iced up a little bit."
The flakes apparently came
from ammonia trapped in the connectors and were not the result of a leak. But
contact with ammonia ice can trigger a lengthy decontamination procedure at the
end of a spacewalk to make sure any traces on the spacesuits have evaporated
before the crew re-enters the station.
Whether those procedures
will be required is not yet known.
In any case, Mastracchio
had no problems connecting M3 and M4 to the jumper box and the crew is pressing
ahead with the other lines and cables. As of 9:20 a.m., the crew was running about an hour ahead of
Hopkins' spacesuit --
serial No. 3011 -- is the same one that suffered a water leak during a July
spacewalk, flooding the helmet of European Space Agency astronaut Luca
Parmitano in a frightening emergency that forced the crew to stop work and beat
a hasty retreat to the safety of the station's airlock.
investigation blamed the leakage on contamination that clogged one or more
filters in the suit's cooling water recirculation system. While the root cause
of the contamination has not yet been determined, the suspect hardware in suit
No. 3011 was replaced and engineers are confident the problem has been
Just in case, the
astronauts positioned water-absorbing pads behind their heads, where the water
entered Parmitano's helmet in July, and used velcro to secure snorkel-like
plastic tubes within easy reach of their mouths. The tubes extend down into the
body of the suit, giving the spacewalkers an unobstructed source of air if
water somehow makes it into either helmet.
The water-absorbing pads
and snorkels should provide more than enough time to reach the safety of the
station's airlock if another leak does, in fact, develop.
During a second spacewalk Monday, the
astronauts plan to remove the faulty pump assembly and temporarily stow it on a
nearby mounting fixture. The replacement pump module then will be installed in
its place and the astronauts will re-connect the electrical lines.
During a third spacewalk
Christmas Day, Mastracchio and Hopkins will re-connect the fluid lines and
close out the replacement module. They also will move the old pump assembly to
the same storage pallet where the replacement pump was mounted.
If the work goes smoothly,
it may be possible to complete the pump module swap out in two spacewalks. But
during the 2010 replacement work, Douglas Wheelock and Tracy Caldwell-Dyson ran
into problems getting the ammonia lines disconnected and a third spacewalk was
Given their past
experience, NASA planners say there's a good chance the Christmas Day spacewalk
will be needed and time has been set aside just in case.
Going into Saturday's EVA,
113 astronauts and cosmonauts representing nine nations had logged 1,094 hours
and 39 minutes of spacewalk time outside the space station, or 45.6 full days.
Mastracchio's time outside during his previous six spacewalks totals 38 hours
and 30 minutes, putting him 23rd on the list of most experienced spacewalkers.