Astronauts complete International Space Station relay box repairs

Spacewalking astronauts have completed urgent repairs to the International Space Station, replacing equipment that failed three days earlier and restoring a back-up for a vital data-relay system.

It took commander Peggy Whitson much longer than expected to install the spare unit. Success finally came after her spacewalking partner, Jack Fischer, blasted the area with nitrogen gas to clear away flecks of metal.

Mission Control noted that the failure had occurred only two days, 21 hours and 38 minutes earlier, “and we are already back in a good position, so excellent work”.

“Very good. We are really happy about that,” said Ms Whitson, who has equalled the record for most spacewalks by an American with 10, and moved up to third place on the all-time spacewalking list.

The failed data-relay unit — recently refurbished with upgraded software — was installed in March. Even though a second unit worked after Saturday’s breakdown, Nasa scrambled to put together a spacewalk so there would be a back-up in case the second unit failed, crippling the system for station cooling and solar energy production.

Ms Whitson had no trouble removing the broken unit, but it took her two tries to install the replacement.

During the first attempt, she discovered what appeared to be metal shavings in the holes for the bolts. Mr Fischer used a cleaning tool — essentially a nitrogen gas blaster — and blew away debris from the three holes.

“I think all three look clean as a whistle,” he reported before Ms Whitson bolted down the spare box.

The data-relay boxes are officially known as MDMs or multiplexer-demultiplexers. They weigh 50lb and measure 14in by 8in by 13in.

Ms Whitson and Mr Fischer carried out a previous spacewalk on May 12. That excursion was cut short by leaking station equipment, leaving two antenna installations undone, and Mr Fischer completed the chore on Tuesday.

It was only the second spacewalk for Mr Fischer, a rookie astronaut who arrived at the orbiting lab last month. He marvelled at the world 250 miles below as he worked, commenting: “Oh my gosh, it’s so beautiful.”

“What’s more awesome than being on @Space_Station? Getting a call from mission control 4 another spacewalk! Dancing w/ the cosmos,” he said in a tweet before going out.

Ms Whitson, the world’s most experienced female astronaut, is more than halfway through an extended nine-month mission, her third spaceflight.

She has spent more time off the planet than any other American and, at 57, is the oldest woman to fly in space.

Tuesday’s excursion gave her 60 hours out in the vacuum, behind only Russia’s Anatoly Solovyev, with 78 hours over 16 spacewalks, and fellow American Michael Lopez-Alegria, with more than 67 hours over 10 trips.