“It was just too much risk for the crew,” said Steve Stich, NASA’s commercial crew program manager.

The highly anticipated decision, one of the most consequential by the space agency in years, is a devastating blow to Boeing, which had argued vehemently that Starliner was safe even though it suffered a series of thruster problems and helium leaks as it brought NASA astronauts Sunita Williams and Barry “Butch” Wilmore to the International Space Station in early June.

The decision means that the autonomous Starliner spacecraft will return to Earth, likely in early September, without anyone on board and that Williams and Wilmore will have their stay on the space station, originally intended to last eight days, extended to about eight months — the next Dragon return flight is scheduled for February.