NASA astronauts gear up for emergency spacewalk scheduled for 23 May

Two astronauts aboard the International Space Station will conduct an emergency spacewalk on Tuesday to replace a failed data relay box which is part of a system to control key station hardware, NASA has said. Tuesday's spacewalk, which expected to begin around 8 a.m. EDT and last for about two hours, will be conducted by Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer of NASA.The space station crew has never been in any danger, and the failure of the data relay box, believed to be internal to the box itself, has had no impact on station activities, NASA said in a statement on Sunday. The multiplexer-demultiplexer (MDM) data relay box failed on Saturday morning. "The cause of the MDM failure is not known. After a review of spacewalk preparations and crew readiness throughout the day Sunday, the decision was made to press ahead with the spacewalk on Tuesday," NASA scientists wrote in a blog post.The data relay box is one of two systems 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. A similar MDM replacement spacewalk was conducted in April 2014 by Expedition 39 crew members Steve Swanson and Rick Mastracchio of NASA.Tuesday's spacewalk will be the 10th spacewalk in Whitson's career and the second for Fischer.