Boeing's chief astronaut Chris Ferguson has pulled out of the first-ever crewed test mission of the "Starliner", the company's new reusable space capsule designed to carry passengers and cargo.
The mission to the international space station is planned for 2021.
In a video message posted on Twitter, the veteran Nasa astronaut said he would continue working on the programme, but with his feet firmly on solid ground.
Boeing's press office later confirmed to Associated Press that Ferguson's daughter's wedding was among his reasons for staying.
Boeing and the other members of the capsule's test crew paid tribute to Ferguson's decision.
He will be replaced as commander by Barry "Butch" Wilmore, a veteran of NASA's space shuttle programme, who has spent a total of 178 days in space over the course of his career.