The astronauts, three American and one Japanese, flew back in the same capsule – named Resilience – in which they launched from NASA’s Kennedy Space Center in November.
A SpaceX Crew Dragon capsule carrying four astronauts back to Earth has splashed down off Florida.
The crew reported they were feeling well after their arrival back on Earth following a nearly six-month mission aboard the International Space Station, NASA said on Sunday.
The capsule splashed down at 2:56 am (0656 GMT) in the dark in the Gulf of Mexico off Panama City after a six-and-a-half hour flight from the ISS, night-vision images relayed by NASA's WB-57 high-altitude research aircraft showed.
Teams aboard the Go Navigator recovery ship retrieved the capsule and hoisted it on to the deck about half an hour later.
It was the first nighttime splashdown for NASA since the crew of Apollo 8 arrived in the Pacific Ocean on December 27, 1968.
Commander Michael Hopkins was the first to emerge after the hatch was opened, doing a little jig as he set foot on deck, followed shortly after by fellow NASA astronaut Victor Glover.
"On behalf of Crew-1 and our families, we just want to say thank you ... It's amazing what can be accomplished when people come together. Y'all are changing the world. Congratulations. It's great to be back," Hopkins said in a NASA tweet.
NASA astronaut Shannon Walker and Japan's Soichi Noguchi were the other two aboard.
The four crew will now be taken out of the spacecraft and receive medical checks before being flown by helicopter to Pensacola to board a plane for Houston to be reunited with their friends and family, NASA said.
Seven astronauts remained on the ISS including a new crew of four who arrived on a different SpaceX craft last week.
✅ Mission complete! @Astro_illini, @AstroVicGlover, Shannon Walker and @Astro_Soichi splashed down off the Florida coast at 2:56 a.m. ET. Tune in at 5 a.m. ET for a post-splashdown news conference: https://t.co/A9sbAYbCl3 https://t.co/4yjbdWOrNJ— NASA's Kennedy Space Center (@NASAKennedy) May 2, 2021
First launch to the ISS from US soil since 10 years
NASA and SpaceX have alternative splash down sites ready, aside from Panama City, if need be.
"We have been practicing to recover the crews day or night," Steve Stich, NASA's Commercial Crew program manager, said shortly before the capsule's departure.
"The ships have lots of lighting," helped by "good moonlight," he said, adding that weather conditions were excellent, with calm seas.
SpaceX boats are expected to reach the capsule about 10 minutes after splashdown.
Astronauts 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.
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 program 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.
🐉 You may now move freely about the cabin.— NASA (@NASA) May 2, 2021
The astronauts have removed their spacesuits and are enjoying one more meal in space before returning to Earth. They'll suit up again before the deorbit burn, about 4.5 hours from now. pic.twitter.com/MOysJzxRzG
'It flew by'
The four astronauts who left Saturday – their mission was called Crew-1 – will splash down in the same capsule in which they traveled into space in November.
With them are freezers with samples from zero-gravity scientific experiments they conducted aboard the ISS.
On Tuesday, departing astronaut Walker handed over command of the ISS to a member of the newly arrived crew, Akihiko Hoshide of Japan.
"While our crew complement time together has been relatively short, it is certainly a time that I will cherish forever," Walker said. "What really is going to remain with me is the camaraderie and the friendship."
In the end the departing astronauts spent 168 days aboard the ISS.
"It flew by. It has really gone by quickly," said Glover.
"All of us, as you can imagine, are very excited about the splashdown because of what it's going to enable, and that's the return to our families," said Hopkins.
"We're all very happy with the mission. I think we're all very excited though to come home as well," he said.
The departure was initially scheduled for Wednesday but postponed twice due to forecasts of bad weather at the splash down site.
In August, when the two astronauts who carried out the test mission splashed down, a flotilla of flag-waving leisure boats had approached the area and had to be shooed away.
Besides the new crew of four, the ISS is still home to another American and two Russians.