The astronauts spent more than 160 days in space and their Crew Dragon spacecraft should return on Sunday.
A SpaceX Crew Dragon capsule carrying four astronauts back to Earth splashed down off the Gulf of Mexico early on Sunday.
Boats retrieved the spacecraft and crew after their six-month mission aboard the International Space Station (ISS). The crew reported they were feeling well, NASA said.
The capsule splashed down at 2:56am (06:56 GMT) in the dark in the Gulf of Mexico off the Florida coast after a six-and-a-half hour flight from the ISS, images relayed by NASA’s WB-57 high-altitude research aircraft showed.
It was the first US splashdown in darkness since Apollo 8’s crew returned from the moon in 1968.
The astronauts should have returned to Earth last Wednesday, but high offshore winds forced SpaceX to pass up a pair of daytime landing attempts. Managers switched to a rare splashdown in darkness to take advantage of calm weather.
All four main parachutes could be seen deploying just before splashdown.
Apollo 8 — NASA’s first flight to the moon with astronauts — ended with a predawn splashdown in the Pacific near Hawaii on December 27, 1968.
Eight years later, a Soviet capsule with two cosmonauts ended up in a dark, partially frozen lake in Kazakhstan, blown off course in a blizzard. That was it for nighttime crew splashdowns — until Sunday.
Astronauts Michael Hopkins, Victor Glover, Shannon Walker, and Japan’s Soichi Noguchi went to space last November as the crew on the first fully operational mission to the ISS aboard a vehicle made by Elon Musk’s SpaceX, which has become NASA’s favored commercial transportation partner.
“We welcome you back to planet Earth and thanks for flying SpaceX,” SpaceX’s Mission Control radioed moments after splashdown. “For those of you enrolled in our frequent flyer programme, you’ve earned 68 million miles on this voyage.”
“We’ll take those miles,” said spacecraft commander Hopkins. “Are they transferrable?” SpaceX replied the astronauts would have to check with the company’s marketing department.
The 167-day mission was the longest for a crew capsule launching from the United States. The previous record of 84 days was set by NASA’s final Skylab station astronauts in 1974.
Seven astronauts remain on the ISS including a new crew of four who arrived on a different SpaceX craft last week. Prior to that, two American astronauts made a test mission to the ISS in May and stayed for two months.
That was the first launch to the ISS from US soil since the end of the Space Shuttle programme in 2011. It was also the first crewed mission run by a private company, as opposed to NASA.
Until then US astronauts had caught rides to the ISS aboard Russian spacecraft.