International Space Station (ISS) astronauts Rick Mastracchio and Mike Hopkins had a successful spacewalk today, but the next in the series to fix a coolant loop problem has been delayed by one day to Tuesday, December 24.  The delay will allow time to resize a backup spacesuit for Mastracchio because the one he wore today had a “configuration issue.”

The spacewalk proceeded very well, with tasks accomplished ahead of schedule.  The crew is changing out a coolant loop pump assembly because a flow control value was not correctly regulating the temperature of ammonia used as a coolant.   After about four and a half hours, Mastracchio, a veteran of six spacewalks, and Hopkins, a spacewalk rookie, had disconnected the large, cumbersome troublesome pump assembly and gotten it secured in a new location on the outside of the ISS.

Ground personnel told Mastracchio that they had a list of other tasks they would like the crew to perform as “get ahead” items and asked for his input.  He replied that his vote was to end the spacewalk at that point.  Earlier he had complained that his feet were cold and ground personnel asked about his temperature, suggesting that might be the reason for his decision to call an early end to the scheduled 6.5 hour spacewalk.   Mastracchio replied that there were “a couple of things” involved in his decision and ground personnel soon agreed that it was time to call it a day.   The spacewalkers returned to the airlock and the spacewalk ended after 5 hours and 28 minutes.

What happened after that is not clear.  A NASA statement said only that during “repressurization of the station’s airlock following the spacewaik, a spacesuit configuration issue put the suit Mastracchio was wearing in question for the next excursion  – specifically whether water entered into the suit’s sublimator inside the airlock.”   

The extra day will give the crew time to get a backup spacesuit ready to replace the one Mastracchio used today.

NASA stressed that today’s problem “is not related to the spacesuit water leak” that happened in July when European astronaut Luca Parmitano’s helmet filled with water.  At a press conference on Wednesday, NASA officials cautioned that they could not “rule out water in the helmet again” but said they had developed new procedures and added two pieces of hardware to the suits to deal with such an eventuality.   That did not happen today, however, the agency said:  “Both Mastracchio and Hopkins reported dry conditions repeatedly” during today’s spacewalk.  It was Hopkins, not Mastracchio, who was wearing the spacesuit that malfunctioned during Parmitano’s spacewalk.

NASA scheduled three spacewalks to fix the coolant loop problem, but the tasks were accomplished so readily today that only two may be needed. 

NASA astronaut Mike Hopkins will conduct his first spacewalk on Saturday.  He will wear the same spacesuit that European astronaut Luca Parmitano was wearing in July when the helmet filled with water for reasons that are still not fully understood.   Nonetheless, NASA has “high confidence” that measures they have taken will prevent a recurrence and, if not, they are adding an absorption pad and a snorkel to the spacesuit to mitigate the situation.

At a press conference today, International Space Station (ISS) program manager Mike Suffredini, ISS flight director Dina Contella, and lead spacewalk officer Allison Bollinger explained their reasoning that the spacewalk will be safe and why it needs to be conducted now.

The precipitating event is a problem in one of the two ISS coolant loops.  A flow control valve is not operating correctly, allowing the temperature of ammonia used as a coolant to drop too low to allow it to enter a heat exchanger that also is in contact with water, lest the water freeze.  The ISS uses water to cool the interior of the ISS, keeping the toxic ammonia on the outside of the station.   The flow control valve is part of a pump assembly that was replaced in 2010, so age is not a factor in its malfunction.   Suffredini said the problem likely is the valve’s electronics and he stressed that the pump itself is working fine and continues to cool equipment on the outside of the station.

The crew is not in danger and critical ISS systems have been moved to the functioning coolant loop, but NASA does not want to remain in that posture for long.   From December 30 to January 9, the Beta angle of the Sun vis a vis the ISS will preclude spacewalks as well as berthing of Orbital Sciences Corporation’s Cygnus spacecraft.  NASA decided yesterday to delay the Cygnus launch that was scheduled for tomorrow until January so the crew can focus on fixing the coolant loop issue before December 30.

Hopkins and fellow NASA astronaut Rick Mastracchio will conduct at least two and perhaps as many as four spacewalks while Japanese astronaut Koichi Wakata operates Canadarm2 in a complex ballet of steps needed to replace the pump assembly.   NASA is currently planning three 6.5 hour spacewalks on December 21, 23 and 25, but that schedule could change depending on how far the astronauts get during the first one. Although Hopkins is a rookie, Mastracchio is a veteran spacewalker with six spacewalks totaling 38 hours and 30 minutes.  

Parmitano provided a chilling account of feeling like “a goldfish in a fishbowl” during his spacewalk on July 16, 2013.  NASA still is not certain why his helmet filled with water.   Suffredini pointed out today that these spacesuits are 35 years old and they had not imagined that such a failure mode could occur.   Now that it has, engineers are trying to figure out exactly why and how.   They have been troubleshooting the issue since July and made some fixes, such as changing the fan pump separator unit, but the root cause remains elusive.  Suffredini said they believe it is related to water that is flowing through the suit that is high in silica content.

Contella said today that until the root cause is known, “we can’t rule out that we would have water in the helmet again,” which is why they have developed new operational procedures and two new pieces of hardware that will be added to the suit.   

Bollinger demonstrated the two items.   One is a “helmet absorption pad” that will be placed at the back of the astronaut’s head.  The pad can absorb 600-800 milliliters (ml) of water.  Astronauts testing it on the ground discovered that it begins to feel “squishy” when it has absorbed about 200 ml, so if a spacewalking astronaut notices squishiness, that’s a signal that he should return to the airlock quickly.  The pads were brought to the ISS on Orbital’s demonstration mission in September/October and on a Soyuz flight.

The other is a snorkel that was fabricated by the crew on orbit.  It will be installed in the spacesuit between the water restraint bag and the front side of the suit.  As “a last resort, if water is encroaching your face … the crewmember can lean down and use [the snorkel] to breathe, to receive fresh oxygen from down near his midsection,”  Bollinger explained.

All three currently planned spacewalks will begin at 7:10 am Eastern Standard Time, with NASA TV coverage beginning at 6:15 am EST.

The press conference is posted on NASA’s YouTube channel.