U.S. Astronauts Begin Spacewalk 250 Miles Above Earth

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(CNN) — Two U.S. astronauts have donned their spacesuits for a spacewalk Wednesday about 250 miles above Earth to carry out maintenance on the International Space Station.

Expedition 45 commander Scott Kelly and flight engineer Kjell Lindgren will be outside the space station for about 6½ hours, NASA said.

The astronauts will “focus on station upgrades and maintenance tasks, including installing a thermal cover on the Alpha Magnetic Spectrometer, which is a state-of-the-art particle physics detector that has been attached to the station since 2011,” the space agency said.

It later said the thermal cover had successfully been fitted about 2½ hours into the spacewalk.

NASA is carrying live coverage of the spacewalk — the first for both men.

The astronauts will carry out a second spacewalk November 6, two days after the 15-year anniversary of continuous human presence aboard the space station.

An international crew of six people live in the station, which orbits Earth every 90 minutes.

In a tweet, NASA astronaut Douglas H. Wheelock explained that the frequent orbits meant half of Wednesday’s spacewalk would take place in darkness, with a sunrise or sunset every 45 minutes.

342 days in space

Kelly arrived at the station in May. He plans to spend 342 days there — the longest stretch of time any U.S. astronaut has spent in space.

Kelly’s mission will allow scientists to study how the human body responds to long-duration space flights. On Earth, scientists will perform parallel studies on Kelly’s identical twin brother, retired astronaut Mark Kelly.

Mark Kelly is the husband of former U.S. Rep. Gabrielle Giffords of Arizona, who left office after being wounded in a January 2011 assassination attempt.