NASA astronaut Peggy Whitson is pictured with an Orbital ATK Cygnus spacecraft (left) during a May 12, 2017 spacewalk outside the International Space Station. Whitson, the station’s commander, and fellow NASA astronaut Jack Fischer will conduct a repair spacewalk on Tuesday, May 23.
CAPE CANAVERAL, Fla. – NASA astronauts will take an unplanned spacewalk Tuesday (May 23) to replace a failed data relay box outside of the , restoring critical redundancy to the orbiting outpost, agency officials said Sunday (May 21).
The failed device, known as a multiplexer/demultiplexer, or MDM, was installed on March 30 during a spacewalk by NASA astronauts , now the station’s commander, and then-flight engineer Shane Kimbrough, who returned to Earth last month. Whitson will perform Tuesday’s spacewalk repair with fellow who arrived at the orbiting laboratory in April. 
The MDM, one of two located on the outside of the station’s S0 segment of the station’s backbone-like main truss, controls exterior U.S. systems, including solar arrays, cooling loops, radiators and other equipment.
The upgraded MDM failed on Saturday (May 20), NASA officials , adding that the crew was never in any danger.
“The cause of the MDM failure is not known,” the statement said.
After the failure, the station switched over to the spare MDM, but NASA wants to restore redundancy as quickly as possible.
Station program managers met on Sunday to assess troubleshooting efforts and decided to replace the failed unit with a spare.
Working inside the station, Whitson spent Sunday assembling and testing a new MDM, which will be installed during a two-hour spacewalk Tuesday. The unit measures 10.5- by 14.9- by 16.4 inches (27- by 38- by 42 centimeters) and weighs 51 lbs. (23 kilograms.)
Whitson and Fischer . The station’s current crew also includes two Russian cosmonauts and French astronaut Thomas Pesquet of the European Space Agency.
The MDM failure and replacement is not expected to impact next week’s launch of a to the station, NASA spokesman Dan Huot said.
Launch of a Falcon 9 rocket with the Dragon freighter currently is targeted for June 1.
Tuesday’s spacewalk is scheduled to begin at 8 a.m. EDT (1200 GMT). NASA’s live webcast coverage will begin at 6:30 a.m. EDT (1030 GMT). , courtesy of .
Irene Klotz can be reached on Twitter at @free_space. Follow us , and . Original article on .