Record setting International Space Station commander Peggy Whitson and rookie American astronaut, U.S. Air Force Colonel Jack Fischer, will undergo an emergency space walk on Tuesday to replace one of the two computers used to control major U.S. systems aboard the spacecraft.

The computer, which serves as the primary computing hub for most the U.S. systems aboard the ISS, went down on Saturday, leaving the five-person crew with no choice but to rely on backup systems to manage the $100 billion space station’s solar power system, radiators, cooling loops and other equipment.

The redundant backup systems used to pick up the slack in the absence of the faulty computer kicked in without any gap in performance, ensuring the crew, who hail from the United States, Russia, and France, were never in any direct danger as a result of the malfunction.

On Sunday, Whitson prepared and tested a spare electronics box intended to replace the failed device attached to the external surface of the space station.  The now defunct computer, called a multiplexer-demultiplexer (MDM) data relay box, has only been in operation since its installation on March 30th of this year.  No details as to what caused the failure have been released by NASA thus far, though they have stated they have said they believe the issue “to be internal to the box itself.”

A similar contingency spacewalk was used to replace another faulty MDM box in April of 2014.  That mission was successfully completed by Steve Swanson and Rick Mastracchio of NASA.

Tuesday’s spacewalk is expected to have a duration of around two hours, including an additional task to be completed by Colonel Fischer, in which he will install a pair of wireless communications antennas on the Destiny Lab as Whitson completes the installation of the new MDM box.