Stuck in space no more, NASA astronauts Butch Wilmore and Suni Williams have returned to Earth, hitching a different ride home to close out a saga that began with a bungled test flight more than nine months ago.

Their SpaceX capsule parachuted into the Gulf of Mexico in the early evening, just hours after departing the International Space Station. Splashdown occurred off the coast of Tallahassee in the Florida Panhandle, bringing their unplanned odyssey to an end.

Within an hour, the astronauts were out of their capsule, waving and smiling at the cameras while being hustled away in reclining stretchers for routine medical checks.

Butch Wilmore being helped after exiting the SpaceX capsule. – Reuters

It all started with a flawed Boeing test flight last spring.

The two expected to be gone just a week or so after launching on Boeing’s new Starliner crew capsule on June 5. So many problems cropped up on the way to the space station that NASA eventually sent Starliner back empty and transferred the test pilots to SpaceX, pushing their homecoming into February. Then SpaceX capsule issues added another month’s delay.

Sunday’s arrival of their relief crew meant Wilmore and Williams could finally leave. NASA cut them loose a little early, given the iffy weather forecast later this week. They checked out with NASA’s Nick Hague and Russia’s Alexander Gorbunov, who arrived in their own SpaceX capsule last fall with two empty seats reserved for the Starliner duo.

“On behalf of SpaceX, welcome home,” radioed SpaceX Mission Control in California.

“What a ride,” replied Hague, the capsule’s commander. "I see a capsule full of grins ear to ear.”

Dolphins circled the capsule as divers readied it for hoisting onto the recovery ship. Once safely on board, the side hatch was opened and the astronauts were helped out, one by one. Williams was next-to-last out, followed by Wilmore who gave two gloved thumbs-up.

NASA congratulates astronauts on return to Earth after nine months stuck in space. – AP

Wilmore and Williams ended up spending 286 days in space — 278 days longer than anticipated when they launched. They circled Earth 4576 times and travelled 121 million miles (195 million kilometres) by the time of splashdown.

While other astronauts had logged longer spaceflights over the decades, none had to deal with so much uncertainty or see the length of their mission expand by so much.

Dressed in re-entry suits, boots and helmets, the astronauts were seen earlier on NASA's live footage laughing, hugging and posing for photos with their colleagues from the station shortly before they were shut into the capsule for two hours of final pressure, communications and seal tests.

NASA astronauts Butch Wilmore and Suni Williams return to Earth. – AP

The astronaut pair had launched into space as Starliner's first crew in June for what was expected to be an eight-day test mission. But issues with Starliner's propulsion system led to cascading delays to their return home, culminating in a NASA decision last year to have them take a SpaceX craft back this year as part of the agency's crew rotation schedule.

Williams told reporters earlier this month that she was looking forward to returning home to see her two dogs and family.

"It's been a roller coaster for them, probably a little bit more so than for us," she said.

The mission has captured the attention of US President Donald Trump, who upon taking office in January called for a quicker return of Wilmore and Williams.

SpaceX CEO Elon Musk, a close adviser to Trump, echoed his call for an earlier return. SpaceX's Crew Dragon is the United States' only orbital-class crew spacecraft, which Boeing had hoped its Starliner would compete with before the mission with Wilmore and Williams threw its development future into uncertainty.

Butch Wilmore, Nick Hague, Suni Williams and Aleksandr Gorbunov. – Reuters

The astronauts will be flown on a NASA plane to their crew quarters at the space agency's Johnson Space Center in Houston for a few days of routine health checks before NASA flight surgeons say they can go home to their families.

"They will get some well-deserved time off, well-deserved time with their families," NASA's Commercial Crew Program chief Steve Stich told reporters. "It's been a long time for them."

Living in space for months can affect the human body in multiple ways, from muscle atrophy to possible vision impairment.

Williams, capping her third spaceflight, has tallied 608 cumulative days in space, the second most for any US astronaut after Peggy Whitson's 675 days. Russian cosmonaut Oleg Kononenko set the world record last year at 878 cumulative days.

Replacement crew

Swept up in NASA's routine astronaut rotation schedule, Wilmore and Williams could not begin their return to Earth until their replacement crew arrived, in order to maintain adequate US staffing levels, according to NASA.

Their replacements arrived on Friday night – four astronauts as part of NASA's Crew-10 mission that briefly put the station's headcount at 11.

Support teams monitor the SpaceX Dragon spacecraft after it landed. – Reuters

"We came prepared to stay long, even though we planned to stay short," Wilmore told reporters from space earlier this month.

He added that he did not believe NASA's decision to keep them on the ISS until Crew-10's arrival had been affected by politics.

"That's what your nation's human spaceflight program's all about," he said. "Planning for unknown, unexpected contingencies. And we did that."

Wilmore and Williams had been doing scientific research and conducting routine maintenance with the station's other five astronauts. Williams had performed two six-hour spacewalks for maintenance outside the ISS, including one with Wilmore.

The ISS, sits about 254 miles (409km) in altitude, is a football field-sized research lab that has been housed continuously by international crews of astronauts for nearly 25 years, a key platform of science diplomacy managed primarily by the US and Russia.

The SpaceX capsule floats in the Gulf of Mexico after landing off the coast of Florida. – AP