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.

The four set to depart are NASA astronauts Anne McClain and Nichole Ayers, Japanese astronaut Takuya Onishi and Russian cosmonaut Kirill Peskov. They're expected to lift off at 7:48 p.m. ET from NASA’s Kennedy Space Center in Florida, aboard a SpaceX Falcon 9 rocket.

SpaceX launch scheduled for Wednesday will carry replacement crew for astronauts who have been stuck on the International Space Station since their troubled Starliner mission.