SpaceX, the private rocket company of billionaire entrepreneur Elon Musk, was forced to scrub a planned launch of two Americans into orbit from Florida.
The mission would have marked the first spaceflight of NASA astronauts from US soil in nine years.
The countdown was halted less than 17 minutes before the SpaceX Falcon 9 rocket was due to lift off from the Kennedy Space Center on Wednesday local time.
Astronauts Doug Hurley and Bob Behnken had been preparing for a 19-hour ride aboard the company’s newly designed Crew Dragon capsule bound for the International Space Station.
The next launch window is set for Saturday afternoon.