Peggy Whitson repairs critical space station system in record-tying 10th spacewalk – USA TODAY

USA Today Network James Dean, Florida Today 7:07 p.m. ET May 23, 2017

Spacewalking astronauts made urgent repairs at the International Space Station on Tuesday, three days after a critical relay box failed. The replacement job fell to commander Peggy Whitson, the world's most experienced female astronaut. (May 23) AP

Outside the International Space Station on Tuesday morning, NASA astronaut Jack Fischer waved while attached to the Destiny laboratory during a spacewalk to replace a failed data relay box and install a pair of wireless communications antennas.(Photo: NASA)

CAPE CANAVERAL Astronaut Peggy Whitson on Tuesday repaired a critical International Space Station system during a nearly three-hour spacewalk that moved her into second place on NASAs career list for most spacewalking time.

Joined by NASAs Jack Fischer, Whitsonswapped out a computer relay box that had failed on Saturday.

Known as a multiplexer-demultiplexer, or MDM, the box helped control the stations solar arrays, radiators and cooling loops, among other systems.

A backup box remained in good shape, but NASA on Sunday ordered the unplanned "contingency" spacewalk to minimize the risk of a backup failure.

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Whitson, the 57-year-old commander of the stations five-person Expedition 51 crew,unbolted the failed relay box and installed a spare as the football field-length research complex orbited 250 miles above the planet.

Fischer, meanwhile, installed wireless communications antennas on the stations Destiny lab module.

The two-hour, 46-minute spacewalk added to Whitsons record-breaking resume.

Last month, she set a new NASA mark for most cumulative days in space with more than 534 days, an achievement celebrated with a call from President Trump.

Tuesdays spacewalk was her 10th, tying the most by a NASA astronaut. In the course of itshe passed two retired NASA colleagues, Jerry Ross and John Grunsfeld, for most time performing spacewalks.

Whitsons career total of 60 hours and 21 minutes of extra-vehicular activity, or EVA, trails NASAs Michael Lopez-Alegria by more than seven hours and Russian cosmonaut Anatoly Solovyev the all-time leader by about 20 hours.

No more spacewalks are scheduled before Whitson's planned returnto Earth in September with Fischer, a 43-year-old flight engineer who completed his second spacewalk Tuesday.

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Peggy Whitson repairs critical space station system in record-tying 10th spacewalk - USA TODAY