The four astronauts of the mission called Crew-2 are due to return to Earth this month after spending about six months in the ISS.

They would normally have to wait for four other astronauts, the three Americans and the German from Crew-3, to arrive aboard the Station.

But the takeoff of their rocket, postponed several times and which had been rescheduled for this weekend, was again canceled "because of unfavorable weather conditions," NASA said in a statement.

Consequence: the space agency is now considering the return of Crew-2 "before the launch" of Crew-3.

"The first possible opportunity" for the undocking of the capsule that will bring Crew-2 back to Earth, including the French, is at 1:05 p.m. Sunday Florida time (6:05 p.m. GMT, 7:05 p.m. in France).

A withdrawal opportunity is possible on Monday, NASA said, without giving a specific schedule.

Once detached from the ISS, the capsule will begin a journey of several hours, the duration of which can vary greatly depending on the trajectory, then it will land off Florida.

As for Crew-3's take-off, the closest launch opportunity is at 9:51 p.m. local on Monday (02:51 GMT Tuesday), but only if NASA does not return Crew-2 on Sunday or Monday.

Crew-3 is scheduled to take off aboard a SpaceX Falcon 9 rocket from Kennedy Space Center in Florida, where astronauts have been in quarantine for days.

"The teams will make their final decision on whether to prioritize the launch of Crew-3 or the return of Crew-2 in the days to come, based on the likelihood of favorable conditions" for either, NASA explained.

These two missions are carried out by NASA in collaboration with SpaceX which now provides regular missions to the ISS from American soil.

"These are complex decisions that change from day to day," Steve Stich, in charge of NASA's commercial program, said in the statement.

"The weather in November can be particularly difficult."

During an exchange with President Emmanuel Macron on Thursday morning, Thomas Pesquet spoke of the uncertainty surrounding his return.

"The last few days are a bit special," he said.

"We still have work to do but our whole to-do list, we've finished it, we're ready to come back."

"Somehow it's almost a blessing," he added.

"These few days, for me, I try to make the most of it, it's a bit like an airlock before I come back to Earth."

© 2021 AFP