Spacewalk Planned to Change Out Failed Relay Box

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Astronaut Peggy Whitson

Astronaut Peggy Whitson is pictured with the Orbital ATK Cygnus resupply ship behind her during a spacewalk on May 12, 2017.

International Space Station Program managers met Sunday and gave approval for a contingency spacewalk no earlier than Tuesday by two Expedition 51 crewmembers to change out a multiplexer-demultiplexer (MDM) data relay box on the S0 truss that failed on Saturday morning. The cause of the MDM failure is not known. A final decision on a firm date for the spacewalk and who will conduct the spacewalk will be made later in the day Sunday.

The data relay box is one of two fully redundant systems housed in the truss that control the functionality of radiators, solar arrays, cooling loops and other station hardware. The other MDM in the truss is functioning perfectly, providing uninterrupted telemetry routing to the station’s systems. The crew has never been in any danger and the MDM failure, believed to be internal to the box itself, has had no impact on station activities.

On Sunday, shortly before managers met to discuss the forward plan for dealing with the failed MDM, station commander Peggy Whitson of NASA prepared a spare data relay box and tested components installed in the replacement. She reported that the spare MDM was ready to be brought outside to replace the failed unit. Back on March 30, Whitson and Expedition 50 commander Shane Kimbrough of NASA conducted a spacewalk to install the MDM with upgraded software that failed Saturday.

A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crewmembers Steve Swanson and Rick Mastracchio.

The spacewalk will last about two hours in duration to replace the failed box. No other tasks are planned for the excursion. It will be the sixth spacewalk conducted from the Quest airlock this year.


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