The four newcomers will spend the next few days learning the station’s ins and outs from Butch Wilmore and Suni Williams. Then it will be time for those two to end their nine-month stay and head home.

SpaceX's Falcon 9 rocket lifted off at 7:03 p.m. ET (2303 GMT) from NASA's Kennedy Space Center in Florida carrying four astronauts who will replace Wilmore and Williams, both of whom are veteran NASA astronauts and retired U.

SpaceX delivered a four-person crew to the International Space Station early Sunday, setting the stage for Barry Wilmore and Sunita Williams to depart.