How does NASA handle astronaut medical issues in space?

NASA astronauts Mike Fincke and Zena Cardman were expected to perform a spacewalk outside the International Space Station on Thursday (Jan. 8), but it was called off Wednesday afternoon (Jan. 7) due to "medical concerns" with an unidentified crew member.

Those concerns apparently grew in the hours that followed, prompting NASA to issue a follow-up statement to its EVA (extravehicular activity) cancellation, indicating that bringing astronauts home early is on the table.

"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," an emailed update from the agency early Thursday reads.

Crew-11 is SpaceX's latest astronaut mission to the ISS, which sent Fincke, Cardman, Japanese astronaut Kimiya Yui and cosmonaut Oleg Platonov to the orbiting lab in early August for a six-month stay. The quartet are currently scheduled to come home sometime after the mid-February arrival of Crew-12.

Three other astronauts are living on the ISS at the moment as well: NASA's Christopher Williams and cosmonauts Sergey Kud-Sverchkov and Sergei Mikayev, who arrived on Nov. 27 aboard a Russian Soyuz spacecraft.

We still don't know which astronaut is experiencing the medical issue; NASA privacy policies prevent the agency from revealing such information.

This is not the first time that NASA has postponed an EVA due to medical concerns. But, if Crew-11 leaves early, it would be the first time that ISS astronauts had to prematurely end their orbital stint for health reasons.

Spacewalks are not a simple endeavor for NASA or its astronauts to undertake. Space is unforgiving, and the suits that keep astronauts safe once they step into the void are complex — they are essentially people-sized spaceships. The process for putting on an EVA suit and preparing for a spacewalk takes up to five hours, and once the airlock opens, there's no speedy way to take the suit off if something goes wrong.

For this reason, NASA doesn't hesitate to pull the plug on a planned EVA if potential issues arise in the days and hours leading up to it. Last summer, for example, NASA officials called off the spacewalk of Expedition 71 astronauts Tracy Dyson and Matt Dominick due to "spacesuit discomfort." At the time, the pair had already begun donning their suits.

In August 2020, NASA astronaut Mark Vande Hei and Japanese crewmate Akihiko Hoshide had their EVA called off days ahead of time due to a "minor medical issue." And, back in 2008, a medical concern led to the replacement of European Space Agency astronaut Hans Schlegel by NASA astronaut Stanley Love for two of three planned spacewalks during their 11-day space shuttle mission to the ISS.

Earlier still, NASA initially considered canceling the EVA of Apollo 9 astronaut Rusty Schweickart in 1969, after he vomited due to space-adaptation sickness early in the mission. On the day of his spacewalk, however, Schweickart convinced NASA officials he was well enough to take on the task and successfully completed the first EVA test of the Apollo program's spacesuit.

When it comes to treating medical issues in space, NASA tries to fully equip its astronauts with the knowledge and tools to address a myriad of issues that might arise in orbit, but trying to predict the unpredictable can be difficult.

In at least one case, pharmaceutical stocks aboard the ISS had to be rationed when an astronaut experienced a blood clot in his or her jugular vein. At the time, NASA stretched out the station's supply of blood thinners for more than 40 days before a cargo mission arrived with a top-up. The astronaut was able to stay aboard the ISS for the planned six months and returned to Earth without incident. (NASA has still not disclosed the identity of the astronaut.)

If NASA decides to bring Crew-11 home early, it's unclear how that would affect upcoming missions to the ISS and the launch schedule at NASA's Kennedy Space Center in Florida. Crew-12 is slated to launch in mid-February, which falls after the first launch window for the upcoming Artemis 2 mission to fly astronauts around the moon, currently scheduled for no earlier than Feb. 5.

Crew-11's potential early departure before Crew-12's arrival would still leave NASA astronaut Chris Williams aboard the ISS to ensure the U.S. portion of the station is occupied. In its emailed statement Thursday morning, NASA indicated that it would provide an update on the situation "within the next 24 hours."