Another SpaceX Falcon 9 rocket was ready to launch with just 33 seconds left on the countdown when it was called to a halt.
Officials says a cruise ship in Cape Canaveral had entered a hazard area that needs to be clear for safety.
The Coast Guard tried to move the ship, but it couldn't happen in time for the launch window.
The launch had already been delayed three times due to weather and SpaceX will try for a fifth on Monday.
The rocket is now set to launch at 6:11 p.m. from Cape Canaveral Space Force Station.
