NASA and SpaceX on Monday delayed for the second time a mission to send four astronauts to the International Space Station due to a “minor medical issue” with a crew member.

“The issue is not a medical emergency and not related to Covid-19,” NASA said in a statement, without giving further details.

The members of “Crew-3” — US astronauts Raja Chari, Kayla Barron and Tom Marshburn, as well as German astronaut Matthias Maurer — will remain in quarantine at the Kennedy Space Center until their launch, the statement said.

The crew were originally due to launch aboard a Crew Dragon spacecraft named “Endurance” fixed atop a Falcon 9 rocket from the Kennedy Space Center in Florida on Sunday, October 31.

But the day before, the flight was postponed to Wednesday to avoid “a large storm system.”

The launch is now scheduled for Saturday, November 6 at 11:36 pm local time (0336 GMT Sunday), from Cape Canaveral in Florida.

NASA did not specify which astronaut was affected by the medical issue.

Crew-3 is part of NASA’s multibillion-dollar partnership with SpaceX that it signed after ending the Space Shuttle program in 2011 and aims to restore US capacity to carry out human spaceflight.

The team will replace four Crew-2 astronauts, including Frenchman Thomas Pesquet, who have been on the International Space Station (ISS) since April.

Crew-3 will spend six months on the orbital outpost and conduct research to help inform future deep space exploration and benefit life on Earth.

Scientific highlights of the mission include an experiment to grow plants in space without soil or other growth media, and another to build optical fibers in microgravity, which prior research has suggested will be superior in quality to those made on Earth.

The Crew-3 astronauts will also conduct spacewalks to complete the upgrade of the station’s solar panels and will be present for two tourism missions, including Japanese visitors aboard a Russian Soyuz spacecraft at the end of the year and the SpaceX Axiom crew, set for launch in February 2022.

Crew-2 had originally been set to return to Earth in early November, but NASA said Monday it would “continue to evaluate” possible dates for their return.

“Mission teams are reviewing options including both direct and indirect handovers for the upcoming crew rotation,” NASA said.