Outside of the space station, Russian and European cooperation has all but collapsed since the Russian invasion of Ukraine. The European Space Agency postponed a rover mission to Mars because it relied on a Russian rocket. And a British satellite internet company, OneWeb, canceled a series of launches that used Russia’s Soyuz rockets, shifting some of them to SpaceX rockets. Russia also said it would cease cooperative science experiments with Germany conducted on the Russian part of the space station. A German astronaut, Matthias Maurer, is currently a member of the crew.

Orbital construction of the International Space Station, a cooperative venture between the United States, Russia, Europe, Japan and Canada, began in 1998 with the launch of the module Zarya. Financed by NASA and built by Russia, it is actually part of the NASA-led half of the space station reflecting American foreign policy at the time, which sought to sustain Russia’s space program during the economic tumult after the collapse of the Soviet Union. Russian and American astronauts permanently moved into the fledging space station on Nov. 2, 2000, and it has been continuously occupied by rotating crews of astronauts ever since.

The Russian and NASA-led segments of the station are separate but tightly connected. The Russians rely on American solar panels for power while Russian cargo ships provide periodic boosts to keep the station from falling into the atmosphere. It is “not really an operation that you can separate and go your own way,” said Joel Montalbano, the program manager for the space station at NASA, during a news conference a couple of weeks ago.

Mr. Montalbano said of the conflict in Ukraine, “We’re aware of what’s going on, but we are able to do our jobs to continue operations.”

The astronauts also may be circumspect when talking with one another in orbit. In February, before Russian troops entered Ukraine, Mr. Vande Hei told KARE, a Minnesota television station, that the crew got along “fantastically” and that Ukraine was not a frequent topic of conversation.

“All I can say is we haven’t talked about that too much,” Mr. Vande Hei said. “I’m not sure we really want to go there.”

But Mr. Kelly, who spent 340 days on the space station in 2015 and 2016, said that if he were still in orbit, he would likely discuss the conflict with his Russian counterparts.