A spacewalk planned for Thursday outside the International Space Station was called off late Wednesday because of a “medical concern” with an unidentified crew member, NASA said in a statement.
An update shortly before midnight said the agency was exploring “all options, including the possibility of an earlier end to Crew 11’s mission.”
NASA 
“These are the situations NASA and our partners train for and prepare to execute safely,” the update said. “We will provide further updates within the next 24 hours.”
While NASA did not identify the astronaut in question or explain the medical issue — standard practice due to privacy concerns — the agency said “the matter involved a single crew member who is stable.”
Space station commander Mike Fincke, flight engineer Zena Cardman, Japanese astronaut Kimiya Yui and Russian cosmonaut Oleg Platonov launched to the space station aboard a SpaceX Crew Dragon ferry ship on August. 1.
Going into the new year, the crew expected to remain in space until their replacements arrive in mid-February. Crew 11’s return to Earth is expected around Feb. 20. That’s still the official plan.
In the meantime, Cardman, 38, and Fincke, 58, a veteran of nine spacewalks on earlier missions, were planning to venture outside the station Thursday to finish building a truss needed to support a set of roll-out solar arrays and to carry out other planned maintenance.
A second spacewalk by two yet-to-be-announced astronauts was planned for next week.
NASA 
But NASA called off the the first spacewalk earlier Wednesday, saying “the agency is monitoring a medical concern with a crew member that arose Wednesday afternoon. Due to medical privacy, it is not appropriate for NASA to share more details about the crew member.”
“The situation is stable. NASA will share additional details, including a new date for the upcoming spacewalk, later.”
In a brief space-to-ground radio exchange just after 2:30 p.m. EST, Yui called mission control in Houston and asked for a private medical conference, or PMC.
Mission control replied that a PMC, using a private radio channel, would be set up momentarily. Yui then asked if a flight surgeon was available and if flight controllers had a live camera view from inside the station.
“Houston, do we still have, like, a camera view in Node 2, uh, 3, lab?” Yui asked.
“We don’t have any internal cameras right now, but we can put the lab view in if you’d like,” the mission control communicator replied.
“I appreciate that,” Yui replied. He then asked: “Do you have like a crew surgeon? … A flight surgeon?”
No additional exchanges were heard. Later Wednesday, NASA’s space station audio stream, normally carried live around-the-clock on YouTube, went silent without explanation.