SpaceX flight aims to bring Starliner astronauts Butch Wilmore and Suni Williams, who have been in orbit for nine months, back to Earth.

SpaceX on Wednesday scrubbed the expected launch of a replacement crew of four astronauts to the International Space Station that would have set in motion the long-awaited homecoming of U.S. astronauts Butch Wilmore and Suni Williams.

A launch pad problem has forced a flight delay to replace NASA's two stuck astronauts. The new crew needs to get to the International Space Station before Butch Wilmore and Suni Williams can head home after nine months in orbit.