The Crew Dragon Endurance shuttle disengaged from the International Space Station (ISS) and began the journey back to Earth, which is expected to last approximately 23 hours.
Ditching off Florida is scheduled for around 6.43 am Italian time on Friday 6 May.
On board are German Matthias Maurer, of the European Space Agency (ESA) and colleagues from NASA Raja Chari, Thomas Marshburn and Kayla Barron.
Before entering the shuttle, whose hatch was closed at 5.20 Italian time, the handover for the ISS command took place between Marshburn and the Russian Oleg Artemyev.
The Space Station crew now consists of seven members, with Artemyev, Denis Matveyev and Sergei Korsakov of the Russian space agency Roscosmos, Samantha Cristoforetti of the European Space Agency (ESA), and Americans Kjell Lindgren, Bob Hines and Jessica Watkins, of NASA.