NASA orders spacewalk for repairs at space station – USA TODAY

A pair of astronauts will venture outside the International Space Station for an emergency space walk. According to Reuters, astronauts will replace a failed computer, one of two that control major U.S. systems aboard the orbiting outpost. USA TODAY

In March 2017, NASA astronaut Peggy Whitson suited up in the U.S. Quest airlock getting ready for a spacewalk outside the International Space Station. Whitson will conduct a spacewalk with Jack Fischer on Tuesday, May 22, 2017. The spacewalk was ordered to replace a data relay box that failed Saturday, May 20, 2017.(Photo: Provided by NASA via Florida Today)

MELBOURNE, Fla. A pair of NASA astronauts will perform a spacewalk outside the International Space Station on Tuesday morning to replace a data relay box that failed over the weekend.

The box is one of two in the middle of the football field-length station that controls solar arrays, radiators, cooling loops and other functions, NASA said.

A backup box, formally called multiplexer-demultiplexer, or MDM, is working and NASA said the station's five-person crew was not in danger.

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"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 reported.

However, after the failure Saturday morning, NASA on Sunday gave the go-ahead toproceed quickly with a two-hour spacewalk by Peggy Whitson and Jack Fischer, limiting the crew's vulnerability to a potential failure by the backup system. It's unknown why the box failed.

Whitson was part of a March 30 spacewalk that upgraded the same data relay box with new software.

On Sunday, she inspected and tested a spare box that she'll install Tuesday.

The spacewalk will be the 10th for Whitson NASA's all-time leader for most days in space with more than 560 and second for Fischer. The pair previously teamed up May 12. Whitson's spacewalk Tuesday will tiethe record for most spacewalks by a U.S. astronaut.

That excursion was cut short because of a leaky umbilical hose inside the space station.

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While Whitson replaces the data relay box, Fischer will install a pair of wireless communications antennas outside the station's Destiny lab module. That job was left undone during the May 12 spacewalk.

Tuesday's "extra-vehicular activity," or EVA, as NASA refers to spacewalks, will be the 201st supporting station assembly and maintenance.

The spacewalk is expected to begin around 8 a.m. Tuesday, possibly earlier, and will be broadcast live on NASA TV.

Contributing: The Associated Press. Follow James Dean on Twitter: @flatoday_jdean

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NASA orders spacewalk for repairs at space station - USA TODAY