NASA Astronauts On ISS To Make Emergency Spacewalk Tuesday To Replace Faulty Component

A multiplexer-demultiplexer (MDM) data relay box aboard the International Space Station failed Saturday, and will be replaced Tuesday during a spacewalk by NASA astronauts Peggy Whitson and Jack Fischer, the space agency announced Sunday. The two-hour "contingency spacewalk" has been given the go-ahead by program managers of the ISS. The MDM data relay box is housed in the S0 truss, and is one of the two such systems, both of which are redundant -- which is to say, both boxes are independent and one can take over in the event the other fails. MDM-1, the failed data relay box, apparently malfunctioned shortly after noon Saturday. Crewmembers tried to restore power to the component multiple times, but were not successful.