The photo released by NASA on May 27, 2011 shows that astronaut Michael Fincke works outside the space station during a spacewalk of the STS-134 mission. (Xinhua/NASA)

WASHINGTON, May 22 (Xinhua) -- NASA astronauts on the International Space Station will conduct a contingency spacewalk on Tuesday to change out a data relay box that failed over the weekend, the U.S. space agency said.

Astronauts Peggy Whitson and Jack Fischer will venture out at around 8 a.m. EDT (12:00 GMT) to replace the device, known as a multiplexer-demultiplexer (MDM) during a mission that is planned to last about two hours, NASA said.

The MDM is one of two fully redundant systems housed outside the orbiting laboratory that control radiators, solar arrays, cooling loops and other station hardware.

"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," NASA said in a statement.

The other MDM is functioning perfectly, providing uninterrupted telemetry routing to the station's systems, it added.

A similar MDM replacement spacewalk was conducted in April 2014.