"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 statement said.
According to NASA, the ISS crew has not been in any danger due to the MDM failure, and the failure is believed to be inside the box itself, so it has 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," NASA said.
According to NASA, the other MDM in the truss is functioning perfectly, providing uninterrupted telemetry routing to the station’s systems.
A similar MDM replacement spacewalk was conducted in April 2014.