A pair of astronauts stuck aboard the International Space Station (ISS) for over nine months may have to wait a little longer to return home after the launch of their replacements was postponed.

The Falcon 9 rocket propelling the NASA-SpaceX Crew-10 mission was set to blast off from Florida’s Kennedy Space Center on Wednesday at 7:48 p.m. (2348 GMT).

But with around 45 minutes left on the countdown clock and the four-member team strapped in, the launch was scrubbed because of a technical issue.

“There was an issue with the hydraulic system on the ground side,” NASA launch commentator Derrol Nail said, adding that “everything was fine with the rocket and the spacecraft itself.”

NASA said the next launch opportunity would be on Friday, cancelling a planned Thursday attempt due to expected “high winds and precipitation.”

Crews were also “working to address a hydraulic system issue with a ground support clamp arm” associated with the launch, NASA said.

NASA duo Butch Wilmore and Suni Williams have been stranded aboard the ISS since June after their Boeing Starliner spacecraft developed propulsion issues and was deemed unfit for their return. It came back empty.

Wilmore and Williams were initially slated for an eight-day mission but were reassigned to Crew-9 after its astronauts arrived in September aboard a SpaceX Dragon. The spacecraft carried only two crew members instead of the usual four to make room for Wilmore and Williams.

That Crew-9 spacecraft now docked at the ISS can only return to Earth after the one carrying Crew-10 arrives.

“We came up prepared to stay long, even though we plan to stay short,” Wilmore said in a recent news conference. “That’s what your nation’s human space flight program is all about, planning for unknown, unexpected contingencies.”

Crew-9 was set to depart on Sunday, weather permitting, for an ocean splashdown off the Florida coast. It was not immediately clear if that timeline was still feasible.

Along with Wilmore and Williams, NASA astronaut Nick Hague and Russian cosmonaut Aleksandr Gorbunov will also be aboard the returning Dragon capsule.