2 US Astronauts Conduct Unplanned, Rapidly Executed Contingency Space Walk on Space Station

Astronaut Jack Fischer waves while attached to the Destiny laboratory during a spacewalk on May 23, 2017 to replace a failed data relay box and install a pair wireless antennas. Credit: NASA

In the space of just 3 days, a pair of NASA astronauts conducted an unplanned and rapidly executed contingency space walk on the exterior of the space station on Tuesday, May 23 in order to replace a critical computer unit that failed over the weekend.

The spacewalk was conducted by Expedition 51 Commander Peggy Whitson – NASA’s most experienced astronaut – and Flight Engineer Jack Fischer aboard the International Space Station (ISS).

This marked the 10th spacewalk for Whitson – who already has the most cumulative spacewalk time by a female and the most time in space by a NASA astronaut. This was Fischer’s second spacewalk.

Furthermore Whitson now moves into third place all-time for cumulative spacewalking time totaling 60 hours, 21 minutes. Only Russia’s Anatoly Solovyev and NASA’s Michael Lopez-Alegria have more spacewalking time to their credit.

Peggy Whitson @AstroPeggy is 3rd place all-time for cumulative spacewalk time with 10 spacewalks totaling 60 hours, 21 minutes. Credit: NASA

NASA managers ordered the spacewalk over the weekend when a computer unit known as multiplexer-demultiplexer-1 (MDM-1) unexpectedly failed Saturday morning, May 20 at 1:13 p.m. Central time.

The cause of the MDM failure is not known, says NASA. Multiple attempts by NASA flight controllers to restore power to the MDM-1 relay box were not successful.

The US dynamic duo successfully changed out the MDM computer relay box with a spare unit on board the station. They also installed a pair of antennas on the station on the U.S. Destiny Laboratory module to enhance wireless communication for future spacewalks.

The MDM functions as a data relay box and is located on the S0 truss on the exterior of the US segment of the ISS, thereby necessitating a spacewalk by astronaut crew members.

After NASA engineers thoroughly assessed the situation and reviewed spacewalk procedures on Sunday, May 21, they gave the go ahead for Whitson and Fischer to carry out the hurriedly arranged extravehicular activity (EVA) spacewalk on Tuesday.

Meanwhile, Whitson worked on Sunday to prepare the spare data relay box and test its components to ensure it was ready for Tuesdays swap out of the failed unit.

“The relay box, known as a multiplexer-demultiplexer (MDM), is one of two units that regulate the operation of radiators, solar arrays and cooling loops.” says NASA.

“Because each MDM is capable of performing the critical station functions, the crew on the station was never in danger and station operations have not been affected.”

The two MDM’s housed in the truss are fully redundant systems.

“The other MDM in the truss is functioning perfectly, providing uninterrupted telemetry routing to the station’s systems.”

The spacewalk began Tuesday morning, May 23 at 7:20 a.m. EDT when the two NASA astronauts switched their spacesuits to battery power.

While Whitson focused on the MDM swap, Fischer worked on the antenna installation.

The unplanned spacewalk marks the second this month by Whitson and Fischer. The first was on May 12 and the 200th overall. The Destiny module antenna installation was deferred from the May 12 spacewalk.

Astronaut Peggy Whitson is pictured May 12, 2017, during the 200th spacewalk at the International Space Station. Credit: NASA

The relatively short EVA lasted a total of two hours and 46 minutes. It concluded at 10:06 a.m. EDT.

Overall this was the 201st spacewalk in support of the space station assembly, maintenance and upgrade. Spacewalkers have now spent a total of 1,250 hours and 41 minutes working outside the orbiting lab complex since its inception.

Spacewalk 201 was also the sixth spacewalk conducted from the Quest airlock in 2017 aboard the ISS.

The International Space Station with its prominent solar arrays and radiators attached to the truss structure was pictured May 2010 from space shuttle Atlantis. Credit: NASA

Stay tuned here for Ken’s continuing Earth and Planetary science and human spaceflight news.

Ken Kremer

UPDATE: Spacewalkers Zip Through Tasks To Fix Broken Computer

UPDATE, 11:42 a.m. EDT: Rick Mastracchio and Steve Swanson finished their spacewalk in just 1 hour and 36 minutes, nearly an hour faster than what NASA budgeted for. Early tests show the replacement computer is working well, providing backup once again for the robotics, solar arrays and other systems on station.

Can two astronauts fix a broken computer quickly on the International Space Station, preventing possible problems with the solar arrays and robotics? Watch live (above) to find out.

The NASA spacewalk involving Rick Mastracchio and Steve Swanson is scheduled to start today (April 23) at 9:20 a.m. EDT (1:20 p.m. UTC), with coverage starting around 8:30 a.m. EDT (12:30 p.m. UTC). The spacewalk is scheduled to last 2.5 hours. Bear in mind that the times could change as circumstances arise.

The computer, also called a multiplexer/demultiplexer (MDM), failed for unknown reasons a couple of weeks ago. While the primary computer is working perfectly and the crew is in no danger, things get more risky if the primary computer also breaks. That’s why NASA worked to get the spacewalkers outside as quickly as possible. You can see a full briefing of the rationale here.

As a note, all non-urgent spacewalks have been suspended because NASA is still working on addressing the recommendations given after a life-threatening water leak took place in a NASA spacesuit last summer. Urgent spacewalks can still go ahead because the agency has implemented safety measures such as snorkels and helmet absorption pads in case of another leak.

That said, in the months since NASA has traced the problem to contamination in a filter in the fan pump separator. After replacing the separator, the leaky spacesuit was used during two contingency spacewalks in December with no water problems at all.

Urgent Spacewalk Must Dance Between Dragon and Progress Spacecraft

It’s a good thing that next week’s urgent spacewalk is pegged as a short one, because the coming days will be hectic for the Expedition 39 crew.

Finding a spot for even a 2.5-hour excursion on the International Space Station was extremely challenging, NASA officials said in a news conference today (April 18), because crew time also is needed for two cargo spacecraft: the SpaceX Dragon launch scheduled for today and subsequent Progress undocking/redocking on station.

Here’s a rundown of some things NASA was juggling as it moves hastily to replace a failed backup computer on the outside of the station. Rick Mastracchio and Steve Swanson are expected to go “outside” on Wednesday (April 23), but if today’s SpaceX launch is delayed the spacewalk will be moved up to Sunday (April 20).

Why it’s urgent

The U.S. portion of the station has 46 computers, with 24 of them external. The multiplexer/demultiplexer or MDM (one of two) controls 12 of these external computers and is responsible for everything for how the solar arrays are pointed to how some robotics operate. It should be noted here that the primary MDM is working just fine, but if it fails with no backup, there will be problems. NASA will lose telemetry or data from the external ammonia cooling systems operating on station (although the systems themselves will work automatically). Some redundant equipment can’t be turned on, either. The agency also won’t be able to point the solar arrays to get power or to move them aside when spacecraft come in, to protect the arrays from thruster plumes (although further below you can see some backups they have for the array problems.)

NASA astronaut Mike Hopkins during a contingency spacewalk in December 2013 to replace a faulty ammonia pump. Hopkins was part of Expedition 37/38. Credit: NASA
NASA astronaut Mike Hopkins during a contingency spacewalk in December 2013 to replace a faulty ammonia pump. Hopkins was part of Expedition 37/38. Credit: NASA

Fixing the spacesuits

Since last summer’s life-threatening water leak, NASA has been moving quickly to fix the spacesuits it has. All non-urgent spacewalks are off the table until at least this summer while NASA addresses a panel’s recommendations to fix the problem. A faulty fan pump separator was swapped out on the bad suit (Suit 3011) last December, but two spacesuits still needed to be fixed on station. The crew spent much of the past week changing out a fan pump separator on Suit 3005 (which will also be used in the spacewalk) and flushing out the cooling lines in the suit and on station, since contamination is believed to have led to the failure. (More parts will arrive on Dragon, but they won’t be used this time, NASA has determined.)

Spacewalk preps on the ground

Also today, NASA astronaut Chris Cassidy was in “the pool” (at NASA’s Neutral Buoyancy Laboratory) simulating the spacewalk. He’s part of a team working to see what could go wrong on the spacewalk and come up with procedures dealing with that. “As best we can we have all those answers in our hip pockets so as they get thrown out on the game day, we can give the crew a quick answer,” he said in an interview Wednesday (April 16) on NASA TV.

Preparing the new computer

A spare MDM is inside the station, but it was an older model that needed to be reconfigured. Astronauts changed out a processing card and did other hardware/software changes to prepare the MDM to sit outside of the station. They also thoroughly tested it to make sure it’s working before mounting it outside. As a point of interest, no one yet knows why the backup MDM failed, but astronauts will inspect the site for damage (and take pictures). It’s expected that once they bring the broken MDM inside, any failed cards will be swapped out and sent to the ground sometime for analysis. The MDM itself will stay on station to be used again, as needs arise.

SpaceX's Dragon spacecraft berthed to the International Space Station during Expedition 33 in October 2012. Credit: NASA
SpaceX’s Dragon spacecraft berthed to the International Space Station during Expedition 33 in October 2012. Credit: NASA

Grappling Dragon

SpaceX’s Dragon is a cargo spacecraft controlled by the ground, but the astronauts need to be ready to nab it with the robotic Canadarm2 once it arrives (now scheduled for Sunday, April 20). The crew has their normal amount of training and preparation for the procedures, then the time it takes to capture the spacecraft, and then the time to unload the vehicle (which is somewhat urgent as there are certain research experiments that need to come off fairly quickly, NASA said.)

Moving the solar array

NASA not only needs to have the solar arrays out of the way from thruster plumes from Dragon and Progress, but it also needs to keep power to the station and configure the arrays so that if the other MDM fails, the arrays will automatically be placed in a safe spot. The array would autotrack for 24 hours after the MDM fails, then go to a “preset angle” that NASA carefully chose. As for whether there would be power shortages on station, NASA says it depends on the sun’s angle and what needs to be done on station at a particular time.

Moving the Progress spacecraft

Russian cargo ship Progress 53 is supposed to undock from the Zvezda service module on Wednesday (April 23) to test an automated rendezvous system that controls approaches to station. Then it’s docking again on Friday (April 25).

Unless otherwise noted, information in this article is based on comments from the following officials in today’s NASA news conference: Mike Suffredini, International Space Station program manager; Brian Smith, International Space Station flight director and Glenda Brown, lead spacewalk officer.