A SpaceX mission that aimed to clear the way for two stranded astronauts to get back to earth has been postponed.

The launch from Florida’s Cape Canaveral Space Force Station was put back due to a hydraulic ground issue. There is another possible launch opportunity on Thursday.

The rocket aimed to fly four new crew members to the International Space Station (ISS) and pave the way for the return of Suni Williams and Butch Wilmore.

The two NASA astronauts flew to space in June but were not able to return on a Boeing spacecraft after it was deemed unsafe. The pair would be able to return to earth within days of the SpaceX mission reaching the ISS.