Because NASA rotates space station crews approximately every six months, this newly launched flight with two empty seats reserved for Wilmore and Williams won’t return until late February. Officials said there wasn’t a way to bring them back earlier on SpaceX without interrupting other scheduled missions.

Lifted by a SpaceX Falcon 9 rocket, two astronauts left Earth on Saturday afternoon, headed to the International Space Station. Such launches, taking a new complement of crew to the space station every six months or so,