NASA has postponed a planned Jan. 8 spacewalk outside the International Space Station due to a “medical concern” with an unnamed crew member.

Mike Fincke and Zena Cardman had been scheduled to step outside the International Space Station (ISS) on Thursday at about 8:00 a.m. EST (1300 GMT), kicking off a roughly 6.5-hour extravehicular activity (EVA). But that spacewalk has been postponed.

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When the spacewalk happens, it will be the first for Cardman and the 10th for Fincke, who will tie the record for most EVAs by a NASA astronaut.

Five American astronauts have 10 spacewalks under their belt to date: Bob Behnken, Stephen Bowen, Chris Cassidy, Michael Lopez-Alegria and Peggy Whitson. The world record is 16, held by cosmonaut Anatoly Solevyev.

The Jan. 8 spacewalk was designed to help prepare one of the ISS’ power channels for the future installation of a new International Space Station Roll-Out Solar Array, or iROSA for short.

“Once installed, the array will provide additional power for the orbital laboratory, including critical support of its safe and controlled deorbit,” NASA officials wrote in a spacewalk preview.

Fincke was designated the EVA’s “crewmember 1” and was set to wear a spacesuit with red stripes, according to the preview. Cardman, “crewmember 2,” was set to wear an unmarked suit.

NASA has also been planning another spacewalk this month, targeted for Jan. 15. On that EVA, two as-yet unnamed NASA astronauts will venture outside the ISS to replace a high-definition camera and install “a new navigational aid for visiting spacecraft,” among other tasks, according to the spacewalk preview.

The two spacewalks this month will be the the first of 2026 and the 278th and 279th EVAs in the space station’s long history.

Editor’s note: This story was updated at 5:30 p.m. ET on Jan. 7 with news of the postponement of the Jan. 8 spacewalk due to a crew member medical issue.