Sunita Williams, Butch Wilmore head home after unexpected nine-month ISS stay

NASA astronauts Butch Wilmore and Sunita Williams departed the International Space Station early Tuesday in a SpaceX capsule for a long-awaited trip back to Earth.

Their week-long test mission got stretched to nine months after their faulty Boeing Starliner craft developed snags.

Wilmore and Williams, two veteran NASA astronauts and retired US Navy test pilots, strapped inside their Crew Dragon spacecraft along with two other astronauts and undocked from the orbiting laboratory for a 17-hour trip to Earth.

The four-person crew, formally part of NASA's Crew-9 astronaut rotation mission, is scheduled for a splashdown off Florida's coast later on Tuesday.

"Crew-9 is going home," said commander Nick Hague from inside the capsule as it slowly backed up and away from the station for what a NASA official described on the live webcast of the event as "the trip downhill."

Hague said it was a privilege to "call the station home" as part of an international effort for the "benefit of humanity."

The NASA official said the weather conditions for the splashdown were expected to be "pristine."

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.

Wilmore and Williams' homecoming caps an end to an unusual, drawn-out mission filled with uncertainty and technical troubles that have turned a rare case of NASA's contingency planning - as well as failures of Boeing's Starliner spacecraft - into a global and political spectacle.

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 in 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.

Trump remarks

The mission has captured the attention of US president Donald Trump, who upon taking office in January called for a quicker return of the two astronauts and alleged without evidence that former president Joe Biden "abandoned" them on the ISS for political reasons.

Trump has also drawn attention for his bizarre remarks, referring to Williams as "the woman with the wild hair" and speculating about the personal dynamic between the two.

"They've been left up there - I hope they like each other, maybe they love each other, I don't know," he said during a recent White House press conference.

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.

286 days in space

Upon splashing down, Wilmore and Williams will have logged 286 days in space - longer than the average six-month ISS mission length, but far short of US record holder Frank Rubio.

His continuous 371 days in space ending in 2023 was the unexpected result of a coolant leak on a Russian spacecraft.

Williams, capping her third spaceflight, will have tallied 608 cumulative days in space, the second most for any U.S. 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 U.S. staffing levels, according to NASA.

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

"We came prepared to stay long, even though we planned to stay short," Wilmore told reporters from space earlier this month, adding 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 have 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, about 254 miles (409 km) 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 U.S. and Russia.

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.

Health risks

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

"Folks like Suni Williams are actually known for their interest in exercise, and so I believe she exercises beyond what is even her normal prescription," according to Rihana Bokhari of the Center for Space Medicine at Baylor College.

Still, the unexpected nature of their extended stay - away from their families and initially without enough packed supplies - has drawn public interest and sympathy.

"If you found out you went to work today and were going to be stuck in your office for the next nine months, you might have a panic attack," Joseph Keebler, a psychologist at Embry-Riddle Aeronautical University, told AFP.

"These individuals have shown unbelievable resilience."

The astronauts will be flown to their crew quarters at the space agency's Johnson Space Center in Houston for several days of health checks, per routine for astronaut returns, before NASA flight surgeons approve they can go home to their families. (Agencies)