The reason for the delay was a problem with the launch ramp.
The new crew of four astronauts, who were already in their capsule when the message came, must reach the ISS before the two Americans, Butch Wilmore and Suni Williams, can finally return home after more than nine months in orbit.
Wilmore and Williams went up to the ISS in June and were initially supposed to spend only about a week there. But Boeing's rocket system, which they traveled with, got such serious safety problems that it now has a flight ban for an indefinite period.
The trouble for Elon Musk-owned Space X seems to be of a milder nature, and now one is aiming for a reserve time for the launch, on Friday night Swedish time.
