SpaceX's Falcon 9 rocket blasted off from NASA's Kennedy Space Center in Cape Canaveral, Florida, Wednesday evening after repeated delays.
The Crew Dragon capsule, which sat atop the Falcon 9 rocket before separation, will take the Crew-3 expedition to the International Space Station, replacing the Crew-2 of NASA, European, and Japanese astronauts who returned to earth Monday.
Crew-3 was initially supposed to launch early Halloween morning, but it was delayed because of bad weather and unspecified medical issues among the astronauts.
Onboard the mission are NASA astronauts Kayla Barron, 34, Raja Chari, 44, Thomas Marshburn, 61, and Matthias Maurer, 51, of the European Space Agency.
The crew is expected to arrive at the ISS roughly 24 hours after liftoff. Their mission, which will include science experiments, maintaining the ISS, and spacewalks, will last six months.
Wednesday's launch comes after four astronauts returned to Earth on Monday, riding with SpaceX to end a 200-day space station mission that began last spring.
The Associated Press contributed to this report.