Astronauts have conducted exactly 200 spacewalks in their ongoing upkeep of the International Space Station (ISS), but when Peggy Whitson and Jack Fischer step out on Tuesday, the maneuver will be with an added sense of urgency. NASA has planned an emergency spacewalk to repair a failed data box, one of only two responsible for controlling certain US hardware aboard the orbiting laboratory.

International Space Station Commander Whitson, who just last month broke the record for the most cumulative time spent in space, will venture outside with NASA flight engineer Jack Fischer to replace a multiplexer-demultiplexer (MDM) data relay box. The box, which failed on Sunday, works as an external computer to control things like radiators, solar arrays and cooling loops, along with other hardware.

Emergency spacewalks aren't exactly common, but aren't unprecedented on the ISS. The same MDM experienced a malfunction back in 2014, forcing NASA astronauts Steve Swanson and Rick Mastracchio to carry out a similar replacement exercise. And in 2013, NASA conducted a series of three emergency spacewalks to correct a critical cooling system failure.

NASA says that the box failure has not placed the crew in danger, and that the second MDM is functioning perfectly. But still, it isn't wasting any time. On Sunday, Whitson began preparing and testing a spare MDM, which is now ready to replace the busted one on the station's S0 truss.

The replacement is expected to take two hours, with Whitson taking part in her tenth spacewalk and Fischer his second. While Whitson replaces the MDM, Fischer will install a pair of wireless communications antennas on NASA's Destiny module.

Source: NASA

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