Astronauts Begin Series Of High-Stakes Spacewalks

2:00 PM, Dec 21, 2013   |    comments
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William Harwood, CBS News

Astronauts Rick 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 International Space Station in a high-stakes attempt to restore a critical coolant loop to normal operation.

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 approaching Africa.

"Quite a view," Hopkins marveled as he floated outside the airlock to begin his first spacewalk.

"Yeah, watch that first step," joked Mastracchio, making his seventh EVA, shorthand for extravehicular activity.

For identification, 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 located.

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 compartments.

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 free floating.

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.

The ammonia 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 schedule.

 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.

An exhaustive 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 resolved.

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 required.

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.

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