After years of delays, Boeing's Starliner spaceship which was poised for launch on Monday night as part of a first crewed test flight to orbit, was delayed yet again.
Just two hours before scheduled takeoff officials said a safety issue had been identified.
"Standing down on tonight's attempt to launch," tweeted NASA chief Bill Nelson. "As I've said before, @NASA 's first priority is safety. We go when we're ready."
The launch would have marked a significant step for both the American multinational corporation and NASA's commercial outsourcing strategy as Boeing scrambles to compete with Elon Musk's SpaceX for a larger share of lucrative NASA business.
Monday's delay comes as Boeing's passenger jet division remains mired in a safety crisis.
NASA strategy
Having a second option for trips to the International Space Station (ISS), in addition to SpaceX's Dragon vehicles, has been a NASA priority ever since its last mission in 2011, leaving the US temporarily reliant on Russian Soyuz rockets.
Starliner astronauts Butch Wilmore and Suni Williams are set to take off from Cape Canaveral Space Force Station at 10:34 pm Monday (0234 GMT Tuesday).
Weather conditions were said to be 95% favorable for launch.
The craft will be sent into orbit by an Atlas V rocket made by United Launch Alliance, a Boeing-Lockheed Martin joint venture. Once in space, the crew will take over piloting the Starliner.
