NASA and SpaceX on Wednesday night scrubbed the Falcon 9 launch of a flight intended to retrieve from the International Space Station astronauts Suni Williams and Butch Wilmore, who have spent nine months in orbit.

A launch pad problem prompted SpaceX to delay a flight to the International Space Station on Wednesday 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.