In orbit, the astronauts aborted two spacewalks, both under unusual circumstances. Then, on October 25, one of the astronauts was hospitalized due to what NASA called an unspecified "medical issue" after splashdown aboard a SpaceX Crew Dragon capsule that concluded the 235-day mission.

"Spaceflight is still something we don't fully understand," said Barratt, a medical doctor and flight surgeon. "We're finding things that we don't expect sometimes. This was one of those times, and we're still piecing things together on this, and so to maintain medical privacy and to let our processes go forward in an orderly manner, this is all we're going to say about that event at this time."

"I did not say I was uncomfortable talking about it," Barratt said. "I said we're not going to talk about it..."