The head of Nasa's human spaceflight programme has stepped down just days before a "historic" launch.
Doug Loverro resigned on Monday, Nasa announced, less than a year after his appointment.
Next week, astronauts Bob Behnken and Doug Hurley will travel to the International Space Station (ISS).
The launch, which involves a rocket and spacecraft made by private firm SpaceX, will be the first crewed mission to depart from US soil in almost a decade.
No official reason for Mr Loverro's departure has been announced, but a leaked copy of an email sent to Nasa employees mentioned a risk taken earlier in the year "because I judged it necessary to fulfil our mission".
"Now, over the balance of time, it is clear that I made a mistake in that choice for which I alone must bear the consequences," the message continued.
While Mr Loverro offered no further explanation, he told the Axios news website that his decision to leave the agency was unrelated to the upcoming launch. "I have 100% faith in the success of that mission," he said.
Mr Loverro was appointed in October last year. His deputy, Ken Bowersox, will become the acting head of human spaceflight.
Next week's launch, which is set for 27 May, will mark the first time that Nasa has launched a shuttle carrying people from US soil since 2011. The rocket and spacecraft were both designed by SpaceX, the private company owned by billionaire Elon Musk.Read More – Source