SpaceX has launched a five-month mission to rescue two astronauts stranded in the International Space Station, sending up a downsized crew on Saturday to bring them home next year.
The capsule rocketed into orbit to fetch the test pilots, whose Boeing spacecraft returned to Earth empty earlier this month because of safety concerns.
NASA's Nick Hague and Russia's Alexander Gorbunov were sent up to retrieve Butch Wilmore and Suni Williams.
Because NASA rotates space station crews approximately every six months, this newly launched flight with two empty seats reserved for Mr Wilmore and Ms 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.
NASA astronaut Nick Hague (right) and Roscosmos cosmonaut Aleksandr Gorbunov were selected to retrieve the other astronauts. (AP: Chris O'Meara)
By the time they return, the pair will have logged more than eight months in space. They were expected to be gone just a week when they signed up for Boeing's first astronaut flight that launched in June.
NASA ultimately decided that Boeing's Starliner was too risky after a cascade of thruster troubles and helium leaks marred its trip to the orbiting complex.
The space agency cut two astronauts from this SpaceX launch to make room on the Dragon capsule's return leg for Mr Wilmore and Ms Williams.
Mr Wilmore and Ms Williams watched the lift-off via a live link sent to the space station, prompting a cheer of "Go Dragon!" from Ms Williams, NASA deputy program manager Dina Contella said.
Ms Williams has been promoted to commander of the space station, which will soon be back to its normal population of seven. Once Mr Hague and Mr Gorbunov arrive on Sunday, four astronauts living there since March can leave in their own SpaceX capsule. Their homecoming was delayed a month by Starliner's turmoil.
Mr Hague noted before the flight that change is the one constant in human spaceflight.
"There's always something that is changing. Maybe this time it's been a little more visible to the public," he said.
Mr Hague was thrust into the commander's job for the rescue mission based on his experience and handling of a launch emergency six years ago.
A Russian rocket failed shortly after lift-off, and the capsule carrying him and a cosmonaut catapulted off the top to safety.
Rookie NASA astronaut Zena Cardman and veteran space flier Stephanie Wilson were pulled from this flight after NASA opted to go with SpaceX to bring the stuck astronauts home.
Promised a future space mission, both were at NASA's Kennedy Space Center, taking part in the launch live stream. Mr Gorbunov remained on the flight under an exchange agreement between NASA and the Russian Space Agency.
"Every crewed launch that I have ever watched has really brought me a lot of emotion. This one today was especially unique," a teary-eyed Ms Cardman said following the early afternoon lift-off.
"It was hard not to watch that rocket lift off without thinking, 'That's my rocket and that's my crew.' "
Moments before lift-off, Mr Hague paid tribute to his two colleagues left behind: "Unbreakable. We did it together."
Once in orbit, he called it a "sweet ride" and thanked everyone who made it possible.
Earlier, Mr Hague acknowledged the challenges of launching with half a crew and returning with two astronauts trained on another spacecraft.
"We've got a dynamic challenge ahead of us," Mr Hague said after arriving from Houston last weekend.
"We know each other and we're professionals and we step up and do what's asked of us."
SpaceX has long been the leader in NASA's commercial crew program, established as the space shuttles were retiring more than a decade ago. SpaceX beat Boeing in delivering astronauts to the space station in 2020, and it is now up to 10 crew flights for NASA.
Boeing has struggled with a variety of issues over the years, repeating a Starliner test flight with no one on board after the first one veered off course.
The Starliner that left Mr Wilmore and Ms Williams in space landed without any issues in the New Mexico desert on September 6, and has since returned to Kennedy Space Center.
A week ago, Boeing's defence and space chief was replaced.
Delayed by Hurricane Helene pounding Florida, the latest SpaceX lift-off marked the first for astronauts from Launch Complex 40 at Cape Canaveral Space Force Station.
SpaceX took over the old Titan rocket pad nearly two decades ago and used it for satellite and station cargo launches, while flying crews from Kennedy's former Apollo and shuttle pad next door.
The company wanted more flexibility as more Falcon rockets soared.
AP