NASA has postponed a spacewalk outside the International Space Station (ISS) and announced the early return of its crew due to a medical issue that arose on Wednesday (Jan. 7) with one of the astronauts on board, the agency said.

The spacewalk was planned for 8 a.m. ET on Thursday (Jan. 8) to finish preparing a power channel where a new solar array is set to be installed on the ISS. American astronauts Mike Fincke and Zena Cardman were scheduled to exit the space station for 6.5 hours in what would have been Cardman’s first spacewalk. (Fincke has already performed nine spacewalks.)

“These are the situations NASA and our partners train for and prepare to execute safely,” a NASA spokesperson wrote in an email update on Thursday.

Nevertheless, the agency has confirmed it will bring Fincke, Cardman and two other astronauts, who are part of the current four-person crew aboard the ISS, home early from their stay at the orbital outpost. “Safely conducting our missions is our highest priority, and we are actively evaluating all options, including the possibility of an earlier end to Crew-11’s mission,” the spokesperson said.

Crew-11 arrived at the ISS on Aug. 2, 2025. Fincke and Cardman were joined by Japan Aerospace Exploration Agency astronaut Kimiya Yui and Roscosmos cosmonaut Oleg Platonov for a six-month mission, after which the astronauts were set to be replaced by Crew-12 as part of the space station’s regular staffing rotation.

Crew-12’s launch is scheduled for mid-February. It is unclear what returning Crew-11 home early would mean for the ISS, as such changes to the usual rotation are highly unusual, but there are other astronauts living on the space station at the moment — including NASA’s Christopher Williams and Russian cosmonauts Sergey Kud-Sverchkov and Sergey Mikayev, who arrived at the orbiting lab aboard a Russian Soyuz spacecraft that destroyed its launching pad in November.

NASA has said it will announce a target return date in the coming days.

Editor’s note: This story has been updated following NASA’s confirmation that Crew-11 will return earlier than originally planned.

Sascha is a U.K.-based staff writer at Live Science. She holds a bachelor’s degree in biology from the University of Southampton in England and a master’s degree in science communication from Imperial College London. Her work has appeared in The Guardian and the health website Zoe. Besides writing, she enjoys playing tennis, bread-making and browsing second-hand shops for hidden gems.