Emergency spacewalk: Here's why NASA astronauts will venture outside space station on Tuesday

New Delhi: Expedition 51 Commander Peggy Whitson and Flight Engineer Jack Fischer will will venture outside the International Space Station (ISS) on Tuesday to replace a failed data relay box, said NASA.

The multiplexer-demultiplexer (MDM) data relay box on the S0 truss failed on Saturday morning.

Tuesday's spacewalk, which expected to begin around 8 a.m. EDT, will last for about two hours in duration to replace the failed box.

NASA Television coverage for the spacecwalk will begin at 6:30 a.m.

The data relay box is one of two systems that control the functionality of radiators, solar arrays, cooling loops and other station hardware.

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 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 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.

Back on March 30, Whitson and Expedition 50 commander Shane Kimbrough of NASA conducted a spacewalk to install the same MDM with upgraded software that failed Saturday.

(With IANS inputs)