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Contingency spacewalk required to replace failed relay box

Peggy Whitson during EVA-42, which took place May 12, 2017. Photo Credit: NASA

Peggy Whitson during EVA-42, which took place May 12, 2017. She will perform a contingency spacewalk on May 23, 2017. Photo Credit: NASA

A data relay box failure outside the International Space Station (ISS) has prompted mission managers to begin planning a contingency spacewalk. On Tuesday, May 23, 2017, NASA astronauts Peggy Whitson and Jack Fischer will venture outside the Quest airlock to replace the failed component.

The failure occurred at about 2:31 p.m. (18:31 GMT) EDT Saturday, May 20. The unit is one of two fully redundant multiplexer-demultiplexer (MDM) data relay boxes on the S0 truss segment at the center of the station’s Integrated Truss Structure. MDMs primarily control the functionality of the outpost’s massive solar arrays and radiators as well as provide power to other station components. The Expedition 51 crew was informed and isn’t in any danger.

An example of an International Space Station multiplexer-demultiplexer. Photo Credit: NASA

An example of an International Space Station multiplexer-demultiplexer. Photo Credit: NASA

Multiple attempts were made to restore power to the failed relay box; however, it was determined the problem was internal to the device and would require a contingency spacewalk to replace. Mission managers met Sunday morning to discuss the plan for the excursion. Because MDMs are fully redundant, there has been no impact on regular station operations.

Even before managers met, Whitson started preparing a spare relay box by testing the components installed inside the replacement. Later in the day, she reported the spare was ready to be taken outside and replaced.

The current relay box was installed less than two months ago during U.S. Extravehicular Activity (EVA) 41, which was performed by Whitson and Shane Kimbrough (Kimbrough returned to Earth just over a week later in Soyuz MS-02). There was nothing wrong with the previous one, it was just being replaced with a more capable version and upgraded software.

However, Kimbrough had some trouble installing the device. It didn’t stay in place when it was inserted into its slot and required him to physically hold it while he used his pistol grip tool – a space-grade power drill – to tighten the central bolt holding the unit.

The contingency spacewalk, likely to be called U.S. EVA-43, will last about two hours. Whitson will be designated as EV-1 and wear the suit with red stripes while Fischer will be designated EV-2 and wear the suit with no stripes.

Whitson will work to replace the data relay box while Fischer will work to install a pair of wireless communications antennas on the Destiny laboratory. The antenna installation was originally planned for the last spacewalk; however, the duration of that EVA was cut short and the task removed.

This will be the sixth excursion from Quest in 2017 and the 201st overall in support of assembly and maintenance of the ISS. The spacewalk is scheduled to begin around 8 a.m. EDT (12:00 GMT). NASA TV coverage will start about 1.5 hours before that.

A similar MDM replacement spacewalk was required in April 2014 during Expedition 39. Then astronauts Steve Swanson and Rick Mastracchio went out for just over 90 minutes during U.S. EVA-26.

This EVA will be Fischer’s second spacewalk. His first occurred less than two weeks ago.

Whitson will be on her 10th EVA, tying the record for the most number of spacewalks for an American astronaut. She already has 57 hours, 35 minutes over 9 excursions under her belt. She only needs 58 additional minutes to put her in third place for the most cumulative EVA time. Just ahead of her will be retired NASA astronaut Michael Lopez-Alegria’s 67 hours, 40 minutes over 10 spacewalks.

Retired Russian cosmonaut Anatoly Solovyev continues to hold the record of most cumulative spacewalk time with 82 hours, 22 minutes over 16 spacewalks.




Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity. You can find him on twitter @TheSpaceWriter.

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